The incidence of schizotypy among cannabis and alcohol users

Evaluation of reliability and validity of the Persian version of Peters et al. delusions inventory (PDI-40) in iranian non-clinical and clinical samples

BACKGROUND

Some individuals may manifest psychotic symptoms that do not fulfill the requisite clinical criteria for a formal diagnosis of psychosis. The assessment of susceptibility to delusions, encompassing both clinical and non-clinical cohorts, frequently makes use of the Peters et al. Delusions Inventory (PDI-40). This study aimed to evaluate the reliability and validity of the Persian version of Peters et al. Delusions Inventory (PDI-40) in Iranian non-clinical and clinical samples.

METHODS

The present study employed a cross-sectional, correlational design in 2020. A total of 1402 Iranian participants were recruited for the study, which consisted of three distinct stages. The first stage involved an Exploratory Factor Analysis (EFA) conducted on a non-clinical sample of 512 participants. The second stage comprising different non-clinical sample 764 participants to perform a Confirmatory Factor Analysis (CFA). In the third stage, a clinical sample of 126 psychotic patients was compared to a non-clinical sample. All participants completed the PDI-40, the Community Assessment of Psychotic Experiences (CAPE-42), and the Depression, Anxiety, and Stress Scale (DASS-21). The internal structure of PDI-40 was examined through the analysis of its factor structure using LISREL 8.8.

RESULTS

The EFA analysis unveiled nine components within Persian version of PDI-40. The CFA analysis demonstrated an excellent fit of the nine-factor structure of Persian PDI-40 to the data. The total score exhibited high internal reliability, as indicated by Cronbach's alpha coefficient of 0.92. Moreover, Persian PDI-40 exhibited satisfactory evidence of convergent validity, as significant correlations were observed between dimensions of PDI-40 and subscales of CAPE-42 and DASS-21. Lastly, findings indicated that psychotic participants scored higher than non-clinical participants in all components of the PDI-40(p < 0.05).

CONCLUSION

Persian version of the PDI-40 demonstrates strong reliability and validity for assessing delusion proneness in both non-clinical and clinical samples in Iran. The observed distinctions between psychotic and non-clinical participants underscore its potential as a valuable tool for discerning delusion proneness in diverse contexts.

Schizotypal traits in a large sample of high-school and university students from Tunisia: correlates and measurement invariance of the arabic schizotypal personality questionnaire across age and sex

BACKGROUND

The main goal of the present study was to examine the characteristics of schizotypal traits and their correlations with genetic (i.e., family history of mental illness), demographic (i.e., age, sex), environmental (e.g., income, urbanicity, tobacco/alcohol/cannabis use), and psychological (i.e., personal history of mental illness other than psychosis) factors in Tunisian high-school and university students. Our secondary goal was to contribute the literature by examining the factor structure and factorial invariance of the Arabic Schizotypal Personality Questionnaire (SPQ) across sex and age (adolescents [12-18 years] vs. young adults [18-35 years]) groups.

METHOD

This was a cross-sectional study involving 3166 students: 1160 (36.6%) high-school students (53.0% females, aged 14.9 ± 1.8); and 2006 (63.4%) university students (63.9% females, aged 21.8 ± 2.3). All students were asked to complete a paper-and-pencil self-administered questionnaire containing sociodemographic characteristics as well as the Arabic version of the SPQ.

RESULTS

The total sample yielded total SPQ scores of 24.1 ± 16.6 out of 74. The SPQ yielded good composite reliability as attested by McDonald's omega values ranging from .68 to .80 for all nine subscales. Confirmatory Factor Analysis indicated that fit of the 9-factor model of SPQ scores was acceptable. This model is invariant (at the configural, metric and structural levels) across sex and age. Except for "Odd or eccentric behavior", all schizotypy features were significantly higher among female students compared to males. Multivariable analyses showed that female sex, being a university student, lowest family incomes, tobacco use, and having a personal history of psychiatric illness were significantly associated with higher positive, negative and disorganized schizotypy subscales scores.

CONCLUSION

Future research still needs to confirm our findings and investigate the contribution of the identified factors in the development of clinical psychosis. We can also conclude that the Arabic SPQ is appropriate for measuring and comparing schizotypy across age and sex in clinical and research settings. These findings are highly relevant and essential for ensuring the clinical utility and applicability of the SPQ in cross-cultural research.

Association between formal thought disorder and cannabis use: a systematic review and meta-analysis

Formal thought disorder (FTD) is a multidimensional syndrome mainly occurring along the psychosis continuum. Cannabis use is known to increase symptoms of psychosis, particularly positive symptoms. However, the impact of cannabis use on FTD in individuals presenting symptoms along the psychosis continuum remains unclear. To address this knowledge gap, we conducted a meta-analysis examining the association between cannabis use and FTD in those individuals. We hypothesized that cannabis would worsen FTD. We conducted a systematic search of the PubMed, ScienceDirect, PsycINFO, Web of Science, Embase and Google Scholar databases up to July 2022. The results were collated through a random-effects model using the statistical software R. Reference lists of included studies were searched for additional relevant publications. Nineteen studies were included, totalling 1840 cannabis users and 3351 non-cannabis users. The severity of FTD was found to be higher in cannabis users (SMD = 0.21, 95%CI [0.12–0.29], p = 0.00009). Subgroup analyses revealed that FTD severity was increased among cannabis users, regardless of the disorder severity: healthy individuals (SMD = 0.19, 95%CI [0.05–0.33], p = 0.02); patients with first-episode psychosis (SMD = 0.21, 95%CI [0.01–0.41], p = 0.04); patients with schizophrenia (SMD = 0.25, 95%CI [0.11–0.38], p = 0.005). Between-group differences were not significant. In line with its already known effect on positive symptoms in psychosis, cannabis use appears to be associated with increased FTD severity all along the psychosis continuum. Future research should consider potential confounding variables such as other substance use disorders and explore how FTD dimensions are impacted by cannabis use.

Schizotypy, Lifestyle Behaviors, and Health Indicators in a Young Adult Sample

Problematic lifestyle behaviors and high rates of physical illness are well documented in people with schizophrenia, contributing to premature mortality. Yet, there is a notable absence of research examining general lifestyle and health issues in participants at risk for psychosis. This form of research may help identify concerns that exist during prodromal periods related to future outcomes. Accordingly, the current study examined lifestyle and health in a nonclinical sample of 530 young adults with varying levels of schizotypy. Increasing symptom severity was associated with greater somatic symptoms and poorer sleep quality across positive, negative, and disorganized domains. Elevated negative and disorganized symptoms were associated with significantly reduced health-related quality of life, while evidence for reduced engagement in health behaviors was largely limited to those with elevated negative schizotypy. No relationships emerged between symptom presentation/severity and body mass index or substance use, although zero-order correlations suggested an association between disorganized schizotypy and nicotine use. The pattern of relationships in the current study was consistent with findings from the ultra-high risk and clinical literature suggesting that lifestyle and health concerns may exist on a continuum with psychosis. Future research should seek to clarify if these patterns are associated with long-term physical or mental health outcomes.

Subjective Impact of the COVID-19 Pandemic on Schizotypy and General Mental Health in Germany and the United Kingdom, for Independent Samples in May and in October 2020

Studies reported a strong impact on mental health during the first wave of the COVID-19 pandemic in March-June, 2020. In this study, we assessed the impact of the pandemic on mental health in general and on schizotypal traits in two independent general population samples of the United Kingdom (May sample N: 239, October sample N: 126; participation at both timepoints: 21) and in two independent general population samples of Germany (May sample N: 543, October sample N: 401; participation at both timepoints: 100) using online surveys. Whereas general psychological symptoms (global symptom index, GSI) and percentage of responders above clinical cut-off for further psychological investigation were higher in the May sample compared to the October sample, schizotypy scores (Schizotypal Personality Questionnaire) were higher in the October sample. We investigated potential associations, using general linear regression models (GLM). For schizotypy scores, we found that loneliness, use of drugs, and financial burden were more strongly corrected with schizotypy in the October compared to the May sample. We identified similar associations for GSI, as for schizotypy scores, in the May and October samples. We furthermore found that living in the United Kingdom was related to higher schizotypal scores or GSI. However, individual estimates of the GLM are highly comparable between the two countries. In conclusion, this study shows that while the general psychological impact is lower in the October than the May sample, potentially showing a normative response to an exceptional situation; schizotypy scores are higher at the second timepoint, which may be due to a stronger impact of estimates of loneliness, drug use, and financial burden. The ongoing, exceptional circumstances within this pandemic might increase the risk for developing psychosis in some individuals. The development of general psychological symptoms and schizotypy scores over time requires further attention and investigation.

Does variation in trait schizotypy and frequency of cannabis use influence the acute subjective, cognitive and psychotomimetic effects of delta-9-tetrahydrocannabinol? A mega-analysis

BACKGROUND

While the acute effects of cannabis are relatively benign for most users, some individuals experience significant adverse effects. This study aimed to identify whether variation in schizotypal personality traits and frequency of cannabis use influence the acute effects of delta-9-tetrahydrocannabinol (THC).

METHODS

Individual participant data from four double-blind, randomised, placebo-controlled, acute crossover studies involving 128 cannabis users were combined for a mega-analysis. Using multilevel linear models and moderation analyses, frequency of cannabis use and schizotypal personality traits were investigated as potential moderators of the subjective, cognitive and psychotomimetic effects of acute THC.

RESULTS

There was evidence of a moderating effect where increased frequency of cannabis use was associated with reduced intensity of subjective (changes in alertness and feeling stoned) and psychosis-like effects following THC when compared with placebo. Moderating effects of cannabis use frequency on acute memory impairment were weak. Trait schizotypy did not moderate the acute psychosis-like effects of THC compared with placebo.

CONCLUSIONS

Our results suggest that a pattern of domain-specific tolerance develops to the acute effects of THC. Tolerance to the alertness-reducing effects occurred more readily than tolerance to psychotomimetic effects. Only partial tolerance to feeling stoned was found, and there was weak evidence for tolerance to memory impairment. Trait schizotypy did not moderate THC's effects on psychotomimetic symptoms.

Prevalence and correlates of psychotic-like experiences in the general population

BACKGROUND

To what extent Psychotic Like Experiences (PLEs) are associated with nonpsychotic psychiatric disorders and whether the number of PLEs is associated with higher rates of psychiatric disorders remains unclear.

METHODS

The sample was composed of 34,653 civilian participants, aged 18 years and older from wave 2 National Epidemiologic Survey on Alcohol and Related Conditions (NESARC). This was a representative sample of the non-institutionalized U.S.

POPULATION

Twenty-two PLEs were assessed. Lifetime prevalence of psychiatric disorders (any mood, anxiety, substance use and personality disorders, PTSD, ADHD, and suicide attempts) according to the number of PLEs were calculated.

RESULTS

Almost a third (26.69%) of respondents reported experiencing at least one type of PLEs. There was a gradual association between the number of PLEs and the presence of a nonpsychotic psychiatric disorder (ranging from 5.68%in participants with no PLEs up to 99.53% in those with five or more PLEs). This association with PLE was significant for each of the 25 psychiatric disorders examined regardless of the number of PLEs. Lifetime prevalence of PLEs were significantly higher among the younger respondents, women, non-married, unemployed, high educational level and those with low family income.

CONCLUSION

There is a gradual increase in the magnitude of the association of the numbers of PLEs for each of the 25 nonpsychotic psychiatric disorders examined. Having at least one PLE is strongly associated with the presence of a psychiatric disorder.

Age moderates the association between frequent cannabis use and negative schizotypy over time

The current study examined whether age and frequent cannabis use interact to influence the trajectories of positive and negative schizotypy over time. Participants were 155 cannabis users, aged 15-24 years old, assessed over a 12-month period at 6-monthly intervals. The analyses examined the influence of age, frequent use, and time on positive and negative schizotypy. The current study found that among frequent cannabis users, younger age was associated with increased negative schizotypy over time, while among occasional cannabis users, younger age was associated with decreasing negative schizotypy over time. The current findings have implications for understanding how cannabis use may influence psychosis risk differently depending on age and frequency of use, as well as bring together past mixed findings on the relationship between negative schizotypy and cannabis use.

Could schizotypy protect against the negative outcomes of borderline traits on alcohol consumption? A cluster analytic study

Schizotypal and borderline personality traits seem to be differently associated to alcohol use in young adult. However, no study has explored co-occurring schizotypal and borderline traits in their link with alcohol consumption. Participants were 1572 students from different French universities who completed self-report questionnaires assessing these three dimensions. A cluster analysis based on the borderline and schizotypal traits scores yielded four distinct groups characterized by low schizotypal and borderline traits (LT), high borderline traits (HB), high schizotypal and borderline traits (HT) and high schizotypal traits (HS). The HS cluster had significantly lower alcohol use than the other three groups. LT and HT clusters did not differ significantly in their alcohol use. Comparison between clusters suggests that schizotypal traits may be protective against the negative impact of borderline traits on alcohol consumption. In the context of a co-occurrence between borderline and schizotypal traits, this study provides important information about their link with alcohol consumption.

Correlation Between Levels of Delusional Beliefs and Perfusion of the Hippocampus and an Associated Network in a Non-Help-Seeking Population

BACKGROUND

Delusions are a defining and common symptom of psychotic disorders. Recent evidence suggests that subclinical and clinical delusions may represent distinct stages on a phenomenological and biological continuum. However, few studies have tested whether subclinical psychotic experiences are associated with neural changes that are similar to those observed in clinical psychosis. For example, it is unclear if overactivity of the hippocampus, a replicated finding of neuroimaging studies of schizophrenia, is also present in individuals with subclinical psychotic symptoms.

METHODS

To investigate this question, structural and pulsed arterial spin labeling scans were collected in 77 adult participants with no psychiatric history. An anatomical region of interest approach was used to extract resting perfusion of the hippocampus, and 15 other regions, from each individual. A self-report measure of delusional ideation was collected on the day of scanning.

RESULTS

The level of delusional thinking (number of beliefs [r = .27, p = .02]), as well as the associated level of distress (r = .29, p = .02), was significantly correlated with hippocampal perfusion (averaged over right and left hemispheres). The correlations remained significant after controlling for age, hippocampal volume, symptoms of depression and anxiety, and image signal-to-noise ratio, and they were confirmed in a voxelwise regression analysis. The same association was observed in the thalamus and parahippocampal, lateral temporal, and cingulate cortices.

CONCLUSIONS

Similar to patients with schizophrenia, non-help-seeking individuals show elevated perfusion of a network of limbic regions in association with delusional beliefs.

Cannabis use in early adolescence is associated with higher negative schizotypy in females

The current study examined the relationship between early onset cannabis use (before age 16) and different schizotypy dimensions, and whether gender moderates these associations. Participants were 162 cannabis users, aged 15-24 years, who completed an online assessment examining alcohol and other drug use, psychological distress, and schizotypy. Participants were divided according to whether or not they had started using cannabis before the age of 16 (early onset=47; later onset=115) and gender (males=66; females=96). The interaction between gender and onset group was significantly associated with the dimension of introvertive anhedonia. Follow-up analyses showed that early onset cannabis use was associated with higher levels of introvertive anhedonia in females only. The current findings suggest that gender is an important moderator in the association between early onset cannabis use, schizotypy, and possibly, psychosis risk.

Psychopathological traits in college students from top-ranking french schools: Do autistic features impair success in science when associated with schizotypal traits?

The link between personality and the interest of individuals for science has not been thoroughly explored. In this report, we studied psychopathological traits in students studying science in French top-ranking institutions. Three hundred and forty seven individuals answered questionnaires assessing autistic and schizotypal dimensions, as well as anxiety, depression symptomatology and attachment quality. A cluster analysis based on autistic and schizotypal traits led to the identification of 4 distinct profiles: a "low trait cluster", a "moderate autistic trait cluster", a "moderate schizotypal trait cluster" and a "high trait cluster" (HTC) composed of individuals with high scores on both autistic and schizotypal scales. Each cluster represented 20.1-27.1% of participants and was clearly different from the three others, both on autistic and on schizotypal dimensions. These groups could be also typified by their level of anxiety, depression or degraded attachment, which are proportional to the extent of psychopathological traits. Moreover, students from the HTC cluster displayed lower academic results, thus implying that autistic traits might impair success in science when they are associated with moderate schizotypal personality features. This study also suggests that depression and anxiety might mediate performance inhibition in the HTC group.

Association between cannabis use and schizotypal dimensions--a meta-analysis of cross-sectional studies

Cannabis consumption can cause abuse and dependence and increase risk of developing psychiatric and somatic disorders. Several literature reviews explored the link between cannabis consumption and schizophrenia but none summarized the rich literature on cannabis and psychometric schizotypy. The aim of our review is to synthesize data from studies that explored the association between cannabis consumption and schizoptypal dimensions. A systematic review of the literature and, when needed, contact with the authors, allowed us to gather data from 29 cross-sectional studies. We compared schizotypy scores between subjects that never used cannabis and subjects that used it at least once ("never vs. ever") and between current users and subjects that do not use cannabis currently ("current vs. other"). We conducted separate analyses for total schizotypy score and each of the three classical schizotypal dimensions (positive, negative, disorganized). For all eight comparisons, the cannabis group ("ever" or "current") had higher schizotypy scores. Differences were in the small or medium range and, with the exception of the negative score in the current vs. other comparison, statistically significant. Cannabis consumption is associated with increased schizotypal traits. More research, using different approaches (e.g. longitudinal studies) is needed to explore the cause of this association.

Gone to Pot - A Review of the Association between Cannabis and Psychosis

Cannabis is the most commonly used illicit drug worldwide, with ~5 million daily users worldwide. Emerging evidence supports a number of associations between cannabis and psychosis/psychotic disorders, including schizophrenia. These associations-based on case-studies, surveys, epidemiological studies, and experimental studies indicate that cannabinoids can produce acute, transient effects; acute, persistent effects; and delayed, persistent effects that recapitulate the psychopathology and psychophysiology seen in schizophrenia. Acute exposure to both cannabis and synthetic cannabinoids (Spice/K2) can produce a full range of transient psychotomimetic symptoms, cognitive deficits, and psychophysiological abnormalities that bear a striking resemblance to symptoms of schizophrenia. In individuals with an established psychotic disorder, cannabinoids can exacerbate symptoms, trigger relapse, and have negative consequences on the course of the illness. Several factors appear to moderate these associations, including family history, genetic factors, history of childhood abuse, and the age at onset of cannabis use. Exposure to cannabinoids in adolescence confers a higher risk for psychosis outcomes in later life and the risk is dose-related. Individuals with polymorphisms of COMT and AKT1 genes may be at increased risk for psychotic disorders in association with cannabinoids, as are individuals with a family history of psychotic disorders or a history of childhood trauma. The relationship between cannabis and schizophrenia fulfills many but not all of the standard criteria for causality, including temporality, biological gradient, biological plausibility, experimental evidence, consistency, and coherence. At the present time, the evidence indicates that cannabis may be a component cause in the emergence of psychosis, and this warrants serious consideration from the point of view of public health policy.

Association between cannabis use, psychosis, and schizotypal personality disorder: findings from the National Epidemiologic Survey on Alcohol and Related Conditions

BACKGROUND

Studies to date showing an association between cannabis use and schizophrenia-spectrum disorders are of relatively small sample sizes with limitations in generalizability. The present study addresses this gap by examining the relationship between cannabis use and psychotic-like symptoms in a large representative community sample.

METHOD

Data were derived from the 2004-2005 National Epidemiologic Survey on Alcohol and Related Conditions (NESARC, Wave 2), a large, nationally representative sample of 34,653 adults from the United States population. We evaluated the association between lifetime cannabis use, psychosis, and schizotypal personality features.

RESULTS

The prevalence of psychosis and schizotypal personality disorder increased significantly with greater cannabis use in a dose-dependent manner. The associations between cannabis use and psychosis were 1.27 (95% CI 1.03-1.57) for lifetime cannabis use, 1.79 (95% CI 1.35-2.38) for lifetime cannabis abuse, and 3.69 (95% CI 2.49-5.47) for lifetime cannabis dependence. There was a similar dose-response relationship between the extent of cannabis use and schizotypal personality disorder (OR=2.02 for lifetime cannabis use, 95% CI 1.69-2.42; OR=2.83 for lifetime cannabis abuse, 95% CI 2.33-2.43; OR=7.32 for lifetime cannabis dependence, 95% CI 5.51-9.72). Likelihood of individual schizotypal features increased significantly with increased extent of cannabis use in a dose-dependent manner.

CONCLUSION

This is the first population-based study to examine the association between lifetime cannabis use, psychosis, and schizotypal personality traits. These results add to evidence that cannabis use may be a risk factor for psychosis liability.

Anxiety and depression in psychosis: a systematic review of associations with positive psychotic symptoms

OBJECTIVE

This review explores the influence of anxiety and depression on the experience of positive psychotic symptoms, and investigates the possibility of a causal role for anxiety and depression in the emergence and persistence of psychosis.

METHOD

A systematic literature search was undertaken, producing a number of papers which comment on the links between anxiety and depression, and the experience of delusions and hallucinations. In addition, evidence which could contribute to our understanding of the causal role of anxiety and depression was highlighted.

RESULTS

The findings show that both anxiety and depression are associated in meaningful ways with the severity of delusions and hallucinations, the distress they elicit and their content. However, the cross-sectional nature of the majority of studies and the focus on certain symptom subtypes tempers the validity of the findings. Data from non-clinical samples, studies which track the longitudinal course of psychosis and those which examine the impact of anxiety and depression on the prognosis for people experiencing psychosis, offer some support for the possibility of an influential role for anxiety and depression.

CONCLUSION

We conclude that anxiety and depression are related to psychotic symptom severity, distress and content and are also linked with sub-clinical experiences, symptom development, prognosis and relapse. These links may imply that anxiety and depression could be targets for therapeutic intervention. The article concludes with suggestions for further research, highlighting avenues which may circumvent the limitations of the body of work as it stands.

Delusion proneness in nonclinical individuals and cognitive insight: the contributions of rumination and reflection

Although previous research demonstrates that clinical individuals with delusions score low on one of the facets of cognitive insight, self-reflection, and high on the other facet, self-certainty, analogous studies of delusion proneness in nonclinical individuals have found that delusion proneness in nonclinical individuals associates with higher levels of both self-certainty and self-reflection. The present study sought to reconcile these inconsistent results by examining the contributions of different facets of self-reflection, rumination and reflection, to delusion proneness. One hundred fifty-two individuals completed three questionnaires: the Beck Cognitive Insight Scale (BCIS), the Peters et al. Delusions Inventory (PDI), and the Rumination-Reflection Questionnaire (RRQ). The results showed that the individuals scoring higher on delusion proneness demonstrated higher levels of both self-certainty and self-reflection on the BCIS as well as higher levels of rumination and reflection on the RRQ. As predicted, the strength of the relationship between BCIS self-reflection and delusion proneness was diminished when rumination was controlled for. These findings suggest that the previously observed positive relation between BCIS self-reflection and nonclinical delusion proneness might be driven, in part, by the ruminative aspect of self-reflection.

Chronic cannabinoid exposure reduces phencyclidine-induced schizophrenia-like positive symptoms in adult rats

RATIONALE

Chronic cannabis use can induce psychotic states that resemble schizophrenia. Yet, schizophrenic patients often smoke cannabis as a form of self-medication to counter the aversive symptoms of schizophrenia. We recently demonstrated an ameliorating effect of cannabinoid self-administration (SA) on negative and cognitive schizophrenia-like symptoms induced experimentally by the non-competitive N-methyl-D-aspartate receptor antagonist phencyclidine (PCP). Whether cannabinoid SA alleviates or exacerbates schizophrenia-like positive symptoms is still unclear.

OBJECTIVES

This follow-up study aimed to evaluate the effect of self-administered cannabinoid on PCP-induced schizotypic positive symptoms in adult rats.

METHODS

Male rats were trained to self-administer either the cannabinoid CB1 receptor agonist WIN 55,212-2 (WIN; 12.5 μg/kg/infusion) or its vehicle (Veh) intravenously. The effects of acute and chronic intermittent intraperitoneal administration of PCP (2.5 mg/kg) on motor parameters were then tested in Veh-SA and WIN-SA.

RESULTS

Cannabinoid SA significantly attenuated the psychotomimetic effects of PCP exposure observed in control rats. Following acute PCP administration, WIN-SA animals displayed more frequent rearing and lower anxiety-like profile than Veh-SA rats. WIN-SA rats also exhibited lower behavioural sensitisation to chronic PCP treatment as demonstrated by reduced hyperlocomotion in response to an acute PCP challenge. In addition, parallel experiments performed in experimenter-administered rats that received WIN at comparable SA doses confirmed the ameliorating effects of cannabinoid exposure on PCP-induced schizotypic behaviours, indicating that motivational effects were not responsible for the ameliorative effects of cannabinoids.

CONCLUSIONS

Our results indicate that cannabis may exert protective effects on positive schizotypic symptoms in adult animals such as hypermotility and anxiety state.

Cannabis use and schizotypy: the role of social anxiety and other negative affective states

Emerging research suggests that cannabis use might be related to psychosis onset in people vulnerable to developing schizophrenia-spectrum disorders. Furthermore, individuals with high-positive and disorganized schizotypy traits report more cannabis use and cannabis-related problems than controls. Social anxiety, a frequently co-occurring schizotypal feature, is related to increased cannabis-related problems in the general population. Building on this research, we explored the impact of social anxiety, measured by the Social Interaction Anxiety Scale (SIAS), and depression and trait anxiety reported on the Brief Symptom Inventory (BSI), on the relationship of schizotypy, measured by the Schizotypy Personality Questionnaire-Brief Revised (SPQ-BR), to cannabis use (n=220 schizotypy, 436 controls) and frequent use and cannabis-related problems among users (n=88 schizotypy, 83 controls) in college undergraduates. Among cannabis users, social anxiety moderated the relationships of schizotypy to frequent cannabis use and more cannabis-related problems in the total schizotypy group, and across high-positive, negative, and disorganized schizotypy subgroups. Depression and trait anxiety also moderated the relationship of schizotypy to frequent cannabis use and more cannabis-related problems, but results varied across high-positive, negative, and disorganized schizotypy subgroups. Results suggest therapeutically targeting negative affective states may be useful in psychosocial intervention for cannabis-related problems in schizotypy.

The psychometric properties of the Peters et al. delusions inventory (PDI) in Taiwan: reliability, validity, and utility

PURPOSE

The Peters et al. Delusions Inventory (PDI) is a commonly used instrument to measure delusion proneness in the general population and includes dimensions that measure distress, preoccupation, and conviction of unusual beliefs. This self-report scale has already been translated into several languages. However, there has not been a validated Taiwanese version previously reported. The aims of the present study were to translate and test the cross-cultural reliability and validity of the PDI in Taiwanese as well as to establish its sensitivity, specificity, and discriminative validity.

METHODS

We administered the questionnaire to a consecutive sample of 253 participants with (n = 154; clinical group including schizophrenia and affective psychosis) or without psychotic disorders (n = 99; non-clinical group). In addition to the Taiwanese version of the PDI (PDI-T), the Taiwanese version of the Brief Psychiatric Symptom Rating Scale (BSRS) was used to measure the severity of psychopathology. We tested the psychometric properties of the PDI-T, including its construct validity, internal consistency, test-retest reliability, concurrent, and discriminative validity.

RESULTS

Overall, the PDI-T showed good construct validity, internal consistency, and stability over time, and it was significantly correlated with the BSRS subscales of psychotic symptoms. The convergent and discriminative validity was satisfactory. The area under the receiver operating characteristic curve of the PDI-T was 0.752. This research found that the most appropriate PDI-T yes/no cut-off scores for determining the absence and presence of delusion proneness were 5 and 13.

CONCLUSIONS

The PDI is a reliable and valid instrument for measuring the dimensionality of delusion proneness and appears to complement subclinical psychosis assessment scales for both epidemiological and clinical research in Taiwan.

Ethnicity, violent offending, and vulnerability to schizophrenia: a pilot study

Previous research has highlighted increased risk for schizophrenia in Afro-Caribbeans as well as over-representation in the prison population. This small-scale study examined the relationship between criminality, ethnicity, and psychosis-proneness in a male prison sample. Twenty British Caucasian and 20 Afro-Caribbean prisoners were divided into equal sub-groups of violent and non-violent offenders. Participants completed measures of schizotypy, delusional ideation, and hostility. Afro-Caribbean offenders scored more highly on negative schizotypy and delusional ideation than their Caucasian counterparts. Violent offenders scored more highly on the positive symptoms of schizotypy than non-violent prisoners. Both ethnicity and violent offending may be relevant factors when considering vulnerability to psychosis in the offending population.

Personality disorders and the 3-year course of alcohol, drug, and nicotine use disorders

CONTEXT

Little is known about the role of a broad range of personality disorders in the course of substance use disorder (SUD) and whether these differ by substance. The existing literature focuses mostly on antisocial personality disorder and does not come to clear conclusions.

OBJECTIVE

To determine the association between the 10 DSM-IV personality disorders and the persistence of common SUDs in a 3-year prospective study of a national sample.

DESIGN

Data were drawn from participants in the National Epidemiologic Survey on Alcohol and Related Conditions (NESARC) who had alcohol dependence (n = 1172), cannabis use disorder (n = 454), or nicotine dependence (n = 4017) at baseline and who were reinterviewed 3 years later. Control variables included demographic characteristics, family history of substance disorders, baseline Axis I disorders and treatment status, and prior SUD duration. Main Outcome Measure  Persistent SUD, defined as meeting full criteria for the relevant SUD throughout the 3-year follow-up period.

RESULTS

Persistent SUD was found among 30.1% of participants with alcohol dependence, 30.8% with cannabis use disorder, and 56.6% with nicotine dependence at baseline. Axis I disorders did not have strong or consistent associations with persistent SUD. In contrast, antisocial personality disorder was significantly associated with persistent alcohol, cannabis, and nicotine use disorders (adjusted odds ratios, 2.46-3.51), as was borderline personality disorder (adjusted odds ratios, 2.04-2.78) and schizotypal personality disorder (adjusted odds ratios, 1.65-5.90). Narcissistic, schizoid, and obsessive-compulsive personality disorders were less consistently associated with SUD persistence.

CONCLUSIONS

The consistent findings on the association of antisocial, borderline, and schizotypal personality disorders with persistent SUD indicates the importance of these personality disorders in understanding the course of SUD. Future studies should examine dimensional representations of personality disorders and the role of specific components of these disorders, biological and environmental contributors to these relationships, and potential applications of these findings to treatment development.

Schizotypy and emotional memory

BACKGROUND

Emotional dysfunction is a core feature of psychotic disorders. One expression of such dysfunction is a reduction of the emotion-induced enhancement of memory which is normally found in healthy individuals. Less severe disruption of emotional processing may also be present in individuals prone to 'unusual' psychosis-like experiences. In this study we investigate voluntary declarative (i.e. explicit or episodic) emotional memory performance, primarily in relation to positive schizotypy (as measured by the unusual experiences scale of the O-LIFE). The effect of negative schizotypy (introvertive anhedonia scale of the O-LIFE) was also explored. We hypothesized that schizotypal individuals (scoring highly on Unusual Experiences) would show reduced memory enhancement.

METHODS

One hundred and two healthy participants viewed a narrated slide-show containing neutral and negative emotional content. They rated the story on a number of affective dimensions and completed a variety of trait measures, including a multi-dimensional measure of schizotypy. Seven days later, a memory test was performed and frequency of involuntary memories related to the slide-show assessed.

RESULTS

The voluntary declarative emotional memory advantage in recall seen in low scorers (25%ile) on unusual experiences was absent in high scorers (75%ile), despite greater subjective fearfulness and emotionality in that group. However, the high scoring group did report experiencing more involuntary memories related to the story. There was no effect of negative schizotypy on declarative emotional memory.

CONCLUSIONS

The emotional memory difficulties seen in studies of schizophrenia may extend to those with a vulnerability to positive psychosis-like experiences. This vulnerability may be expressed in both voluntary declarative - as well as involuntary - emotional memory performance.

Cannabis use and risk of psychosis: an etiological link?

Objective – The nature of the link between cannabis use and psychosis remains to be clarified. Method – The paper reviews the evidence suggesting that cannabis may be a risk factor for psychosis onset. Results – Cross-sectional and retro- spective epidemiological studies show that individuals with psychosis use cannabis more often than other individuals in the gener- al population. It has long been considered that this association is explained by the self-medication hypothesis, postulating that cannabis is used to self-medicate psychotic symptoms. This hypothesis has been recently challenged by several prospective stud- ies carried out in population-based samples, showing that cannabis exposure is associated with an increased risk of psychosis, pos- sibly by interacting with a pre-existing vulnerability for these disorders. A dose-response relationship was found between cannabis exposure and risk of psychosis, and this association was independent from potential confounding factors such as exposure to other drugs and pre-existence of psychotic symptoms. However, the diagnostic specificity is weak, as cannabis exposure may be a risk factor for the occurrence of a large spectrum of psychiatric disorders, ranging from schizophrenia to mood and anxiety disorders. Conclusion – Considering the growing number of adolescents exposed to cannabis, the impact of this substance on the population mental health should be further explored.

Cannabis and psychometrically-defined schizotypy: use, problems and treatment considerations

Cannabis use is associated with onset of psychosis in individuals vulnerable for developing schizophrenia-spectrum disorders. The present study addressed three knowledge gaps pertaining to this issue: 1) clarifying the incidence of cannabis use in schizotypal individuals, 2) examining how cannabis use is related to psychosocial and physiological problems in schizotypy and interest in treatment, and 3) examining how cannabis use is associated with positive, negative and disorganization features of schizotypy. Scores from a measure of schizotypal traits were used to trichotomize 1665 young adults into schizotypy (top 5% of scorers), non-schizotypy (bottom 50% of scorers) and "unconventional" (scorers within the 50th to 85th percentile) groups. Nearly a quarter of the schizotypy group endorsed cannabis use at least weekly, a rate nearly two to four times that of the other groups. The schizotypy group also reported a much greater frequency of cannabis-related problems compared to the other groups. Despite this, interest in treatment for cannabis use in the schizotypy group was not elevated. Interestingly, 85% of individuals in the schizotypy group reported interest in psychological/psychiatric treatment more generally. Cannabis use was not associated with abnormal patterns of positive or disorganized schizotypy traits in the schizotypy group relative to the other groups. However, cannabis use was associated with lower severity of negative traits. Implications of these results are discussed.

Psychotic-like experiences in major depression and anxiety disorders: a population-based survey in young adults

OBJECTIVE

Population-based surveys have confirmed that psychotic-like experiences are prevalent in the community. However, it is unclear if these experiences are associated with common mental disorders. The aim of this study was to examine the prevalence of psychotic-like experiences in those with affective and anxiety disorders.

METHODS

Subjects were drawn from the Mater-University of Queensland Study of Pregnancy. Delusion-like experiences were assessed with the Peters Delusional Inventory (PDI). The Composite International Diagnostic Interview (CIDI) was used to identify individuals with Diagnostic and Statistical Manual of Mental Disorders (Fourth Edition) lifetime diagnoses of major depression, anxiety disorder, substance use/dependence, and psychotic disorders. The influence of affective and anxiety disorders on PDI and CIDI psychosis-related items' scores were assessed with logistic regression, with adjustments for age, sex, and the presence of the other comorbid psychiatric diagnoses.

RESULTS

Having either a lifetime diagnosis of major depressive disorder or an anxiety disorder was associated with significantly higher PDI total scores (highest vs lowest quartile adjusted odds ratios [ORs] and 95% confidence intervals [CIs] = 4.43, 3.09-6.36; 3.08, 2.26-4.20, respectively). The odds of endorsing any CIDI hallucination or delusion item was increased in those with a major depressive or anxiety disorder. The presence of current anxiety disorder symptoms was significantly associated with PDI score (OR = 5.81, 95% CI = 3.68-9.16).

CONCLUSION

While psychotic-like experiences are usually associated with psychotic disorders, individuals with depression and anxiety are also more likely to report these symptoms compared with well individuals. Psychotic-like experiences are associated with a range of common mental disorders.

Synthetic delta-9-tetrahydrocannabinol elicits schizophrenia-like negative symptoms which are distinct from sedation

OBJECTIVE

It is unknown if cannabis recreates the negative symptoms of schizophrenia.

METHODS

Healthy male volunteers (n = 22) completed two experimental sessions in which they received intravenous (IV) delta-9-tetrahydrocannabinol (THC) 2.5 mg or placebo in a randomised counterbalanced order. Negative symptoms were rated using the self-reported community assessment of psychic experiences scale (CAPE). Sedation was rated using the mood-adjective check-list (UMACL). Plasma concentrations of THC were measured over the course of the study. Data were analysed by non-parametric tests.

RESULTS

Participants reported an increase in negative symptoms from baseline under THC but not placebo conditions (p < 0.001). Negative symptoms showed no relationship with self-rated sedation or plasma concentrations of THC.

CONCLUSIONS

At plasma concentrations resembling recreational use, THC elicited schizophrenia-like negative symptoms which were not merely attributable to sedation. In the community, negative symptoms may be an adverse effect of cannabis use.

Substance use in adolescence and psychosis: clarifying the relationship

Adolescence is a time of exploration of the self, and this exploration may involve the use of alcohol and drugs. Sadly, for some, adolescence also marks the first signs of a psychosis. The temporal proximity between the onset of substance use and of psychosis has been the cause of much debate. Here we review the association of alcohol, cannabis, stimulants, and other drugs with psychosis, and we conclude that the use of cannabis and the amphetamines significantly contributes to the risk of psychosis.

Hyper-priming in cannabis users: a naturalistic study of the effects of cannabis on semantic memory function

Psychotic symptoms have theoretically been linked to semantic memory impairments in patients with schizophrenia. Little is known of the effects of cannabis, the world's most popular illicit drug, on semantic memory and whether they are linked to the psychotomimetic states elicited by the drug. Thirty-six cannabis users were tested whilst under the influence of cannabis. They were then tested again when not intoxicated and compared with 38 non-drug using controls. Semantic memory was assessed using a semantic priming task with a long and short stimulus onset asynchrony (SOA) to differentiate automatic and controlled processing. Under the influence of cannabis, users showed increases in both automatic semantic priming and schizotypal symptoms compared with controls. When abstinent, cannabis users exhibited hyper-priming at long SOAs. Cannabis users did not differ from controls in either trait schizotypy or state schizotypy when not intoxicated. Acute cannabis use increases schizotypyal symptoms and may increase automatic semantic priming in recreational users of this drug. When drug-free, cannabis users did not differ from controls in schizotypy but did show hyper-priming at the long SOA. The acute increase in automatic semantic priming may be one factor contributing to the psychotomimetic effects of cannabis.

Superstitious conditioning as a model of delusion formation following chronic but not acute ketamine in humans

BACKGROUND

Ketamine has previously been shown to induce delusion-like or referential beliefs, both acutely in healthy volunteers and naturalistically among nonintoxicated users of the drug. Delusions are theoretically underpinned by increased superstitious conditioning or the erroneous reinforcement of random events.

MATERIALS AND METHODS

Using a novel and objectively measured superstitious conditioning task, experiment 1 assessed healthy volunteers before and during placebo (n = 16), low-dose (n = 15), and high-dose ketamine (n = 16) under randomized and double-blind conditions. Experiment 2 used the same task to compare ketamine users (n = 18), polydrug controls (n = 19), and nondrug-using controls (n = 17).

RESULTS

In experiment 1, ketamine produced dose-dependent psychotomimetic effects but did not cause changes in superstitious conditioning. Experiment 2 found increased levels of superstitious conditioning among ketamine users compared to polydrug and nondrug-using controls, respectively, as evidenced by both objective task responses and subjective beliefs following the task.

CONCLUSIONS

Results indicate that chronic but not acute exposure to ketamine may increase the propensity to adopt superstitious conditioning. These findings are discussed in terms of acute and chronic ketamine models of delusion-like belief formation in schizophrenia.

Associations between past alcohol, cannabis, and cocaine use and current schizotypy among first-degree relatives of patients with schizophrenia and non-psychiatric controls

Associations between past use of alcohol, cannabis, and cocaine and various domains of schizotypy were examined in first-degree relatives of patients with schizophrenia and non-psychiatric controls. Substance use was operationalized in three ways: (1) having ever used the substance, (2) age at first use, and (3) past frequency/amount of use during three time periods in late adolescence/early adulthood. Schizotypy was assessed using the Schizotypal Personality Questionnaire (SPQ). Participants who had ever used cannabis had significantly higher cognitive-perceptual, interpersonal, and total schizotypy scores compared to those who had not. Younger age of alcohol use onset was associated with more schizotypy in adulthood, and younger age of first cannabis use was related to more interpersonal schizotypy. More frequent/heavier use of alcohol in the 25-29 age-range, and cannabis in early adulthood, were associated with more schizotypy. The use of addictive substances, particularly cannabis, is related to schizotypy in complex ways.

Schizotypy and nicotine, alcohol, and cannabis use in a non-psychiatric sample

Schizotypy is a multidimensional personality construct that is characterized by perceptual abnormalities, social withdrawal, mild suspiciousness, and odd thinking patterns. This study examined the relationship between four dimensions of self-reported schizotypy and substance use involving nicotine, alcohol, and cannabis, in undergraduate students. Results showed that higher levels of disorganized schizotypy, or odd thinking and behavior, were associated with greater indices of use of all three substances. Furthermore, higher cognitive-perceptual schizotypy was selectively associated with cannabis use. Results confirm findings of recent research that has discovered associations among schizotypy and substance use, highlighting links between behavioral traits and use of nicotine, alcohol, and cannabis. This study is one of the first to examine a wide range of schizotypy domains, and to show selective effects of the disorganized domain of schizotypy.

Schizotypy and false memory

Using the Deese-Roediger-McDermott (DRM) paradigm the present study examined the relationship between schizotypy and recognition memory. Participants scoring in the upper and lower quartile ranges for schizotypy (Schizotypal Personality Questionnaire brief version; SPQ-B) and on each of the SPQ-B subscales (cognitive-perceptual, interpersonal and disorganized) were compared on true and false memory performance. Participants scoring in the lower quartile range on the cognitive-perceptual subscale recognised a higher proportion of both true and false memories than those scoring in the higher quartile range. Participants scoring in the upper quartile on the interpersonal factor recognised fewer true items than those in the lower quartile range. No differences were found for overall schizotypy or on the disorganized subscale.

Polydrug use, cannabis, and psychosis-like symptoms

OBJECTIVE

To examine psychosis-like symptoms in users of legal and illicit drugs.

METHODS

Schizotypal Personality Questionnaire (SPQ) scores were compared in groups of people with different exposure to cannabis, with the use of other drugs serving as a covariate. Supplemental analyses compared users of legal and illicit drugs with cannabis use as a covariate.

RESULTS

Weekly (n = 111) and monthly (n = 136) cannabis users had higher scores on the SPQ than former (n = 143) and non-users (n = 81). The use of other drugs accounted for the links between cannabis and schizotypy. Lifetime use of psychomotor stimulant drugs plus ecstasy accounted for associations between cannabis and scores on the SPQ and its different subscales. Dividing groups by type of drug use revealed that those who used only cannabis and legal drugs (CLDs) (n = 126) were no different from those who used only legal drugs (LDs) (n = 74) but both groups scored significantly lower on the SPQ than polydrug users (n = 247). When controlling for marijuana use in the last month, the significant difference across drug use groups remained.

CONCLUSIONS

The results suggest that research on marijuana and schizotypy requires careful assessment of the use of other drugs, especially psychomotor stimulants and ecstasy.

Correlates of delusion-like experiences in a non-psychotic community sample

OBJECTIVE

Several large population-based studies have reported that otherwise-well individuals endorse items related to delusion-like experiences. The aim of the present study was to examine selected correlates of delusion-like experiences in a sample of non-psychotic individuals.

METHOD

Subjects (n=310) were screened with the Diagnostic Interview for Psychosis in order to exclude psychotic disorders. Delusion-like experiences were assessed with the Peters Delusional Inventory (PDI). Non-parametric statistics were used to assess the relationship between total PDI score and a range of demographic (age, sex, migrant status, paternal age), physical (minor physical anomalies) symptom-related variables (hallucinations, awareness of thought disorder) and family history of mental illness.

RESULTS

The median (range) PDI score was 4 (0-26), while one-third of the subjects endorsed seven or more items. The presence of a family history of any psychiatric condition was significantly correlated with a higher PDI score. PDI score was significantly positively correlated with endorsement of hallucinations and awareness of thought disorder. PDI was not significantly associated with sex, family history of schizophrenia, paternal age, migrant status nor scores related to minor physical anomalies. There was a trend level association between younger age and higher PDI score.

CONCLUSION

Delusion-like experiences are relatively common in non-psychotic individuals. The association with a family history of mental disorders provides clues to the mechanisms underlying the profile of delusion-like experience.

Effects of cannabidiol on schizophrenia-like symptoms in people who use cannabis

Cannabis contains various cannabinoids, two of which have almost opposing actions: Delta9-tetrahydrocannabinol (Delta9-THC) is psychotomimetic, whereas cannabidiol (CBD) has antipsychotic effects. Hair samples were analysed to examine levels of Delta9-THC and CBD in 140 individuals. Three clear groups emerged: ;THC only', ;THC+CBD' and those with no cannabinoid in hair. The THC only group showed higher levels of positive schizophrenia-like symptoms compared with the no cannabinoid and THC+CBD groups, and higher levels of delusions compared with the no cannabinoid group. This provides evidence of the divergent properties of cannabinoids and has important implications for research into the link between cannabis use and psychosis.

Measuring psychosis proneness in a nonclinical Korean population: is the Peters et al Delusions Inventory useful for assessing high-risk individuals?

OBJECTIVES

We examined the psychometric properties of the Korean version of the Peters et al Delusions Inventory (PDI) 40 and investigated the distribution of delusional ideation in a nonclinical population. We also used the item response theory to evaluate the usefulness of the PDI in measuring the risk for psychosis.

METHODS

A total of 310 nonclinical individuals completed the Korean PDI-40, the Magical Ideation Scale (MIS), and the Schizotypal Personality Scale (STA). In addition, 60 psychotic inpatients with delusions completed the PDI-40. Among 310 individuals, 124 participated in a follow-up study 6 months after completing their original questionnaire.

RESULTS

The PDI-40 revealed a slightly skewed distribution, but the score range was similar to that of the British population. Scores were negatively correlated with age, but no sex differences were found. The Korean PDI-40 exhibited good internal consistency and test-retest reliability. The PDI was significantly correlated with the MIS and the STA. Ten components were extracted through a principal component analysis with varimax rotation. The test results using item response theory revealed 39 items as the items which individuals with very high level of psychosis proneness will answer as "yes." Moreover, all items yielded "above moderate" discrimination in terms of psychosis proneness.

CONCLUSIONS

We confirmed the reliability and validity of the Korean PDI-40. The usefulness of the PDI-40 in a nonclinical population was replicated in the Korean sample. The PDI-40 can be used as an informative device when investigating "psychosis proneness" in a group at high risk for psychosis.

Affect processing and positive syndrome schizotypy in cannabis users

While cannabis is associated with positive syndrome schizophrenia (SZ), it is unclear whether cannabinoids are also related to negative symptoms such as affective blunting. We examined whether cannabis use is associated with schizotypy and utilized event-related potentials (ERPs) to assess affect processing. Cannabis users demonstrated increased P300 amplitudes for unpleasant trait words, and demonstrated higher positive syndrome schizotypy which correlated with levels of cannabis use. The cannabis group also exhibited lower negative syndrome schizotypy. The lack of blunted responses during the affect ERP and decreased negative subscale schizotypy scores provide evidence that the endocannabinoid theory of schizophrenia may be primarily relevant in relation to positive syndrome SZ.

Mixed-handedness is associated with the reporting of psychotic-like beliefs in a non-clinical Italian sample

Atypical handedness has been repeatedly reported in schizophrenia, with quantitative review of evidence showing an increase of non-right-handedness in patients diagnosed with schizophrenia. Mixed-handedness is also higher among non-clinical people scoring high on questionnaires aimed at measuring psychosis-proneness. However, the greatest part of information on non-clinical samples came from samples collected in North America or in the UK: differences by countries in the socio-cultural pressure to use the right hand could influence the results. In this study 604 Italian non-clinical participants (248 males, 41.1%; 356 females, 58.9%; mean age=34.5+/-11.9) completed the Annett Hand Preference Questionnaire (HPQ), the General Health Questionnaire (GHQ), and the Peters et al. Delusions Inventory (PDI). In the sample, 527 subjects (87.3%) were classified on the HPQ as right-handed, 53 (8.8%) were classified as mixed-handed, and 24 (4.0%) were classified as left-handed. Mixed-handed scored statistically higher on the PDI than the right-handed and left-handed, but right-handed and left-handed did not differ from each other on a statistical ground. The difference by handedness was specific for PDI, since scores on the GHQ-12 did not differ by handedness group. The links between mixed-handedness and psychosis-proneness in non-clinical samples are a reliable finding, deserving further investigation as a model for the risk of schizophrenia.

Cannabinoids and Psychosis

Recent epidemiological studies and advances in understanding of brain cannabinoid function have renewed interest in the long-recognized association between cannabinoids and psychosis. This chapter presents evidence supporting and refuting the association between cannabinoids and psychosis. Cannabinoids can induce acute transient psychotic symptoms or an acute psychosis in some individuals. What makes some individuals vulnerable to cannabinoid-related psychosis is unclear. Also clear is that cannabinoids can also exacerbate psychosis in individuals with an established psychotic disorder, and these exacerbations may last beyond the period of intoxication. Less clear is whether cannabis causes a persistent de novo psychosis. The available evidence meets many but not all the criteria for causality, including dose-response, temporality, direction, specificity, and biological plausibility. On the other hand, the large majority of individuals exposed to cannabinoids do not experience psychosis or develop schizophrenia and the rates of schizophrenia have not increased commensurate with the increase in rates of cannabis use. Similar to smoking and lung cancer, it is more likely that cannabis exposure is a component cause that interacts with other factors, for example, genetic risk, to "cause" schizophrenia. Nevertheless, in the absence of known causes of schizophrenia, the role of component causes such as cannabis exposure (exogenous hypothesis) is important and warrants further study. There is also tantalizing evidence from postmortem, neurochemical, and genetic studies suggesting CB1 receptor dysfunction (endogenous hypothesis) in schizophrenia that warrants further investigation. Further work is necessary to identify those factors that place individuals at higher risk for cannabinoid-related psychosis, to identify the biological mechanisms underlying the risks and to further study whether CB1 receptor dysfunction contributes to the pathophysiology of psychotic disorders.

Association between aggressiveness, schizotypal personality traits and cannabis use in Swiss psychology students

Associations between aggressiveness, schizotypal traits, and self-declared cannabis consumption were explored in Swiss psychology students (n = 205). Higher hostility levels were strongly associated with more pronounced schizotypal traits, whereas frequency of cannabis use was not. Therefore, earlier reported correlations might be due to a subgroup of hostile consumers.

Anxiety and depression symptoms in psychometrically identified schizotypy

The neurodevelopmental vulnerability for schizophrenia appears to be expressed across a dynamic continuum of adjustment referred to as schizotypy. This model suggests that nonpsychotic schizotypic individuals should exhibit mild and transient forms of symptoms seen in full-blown schizophrenia. Given that depression and anxiety are reported to be comorbid with schizophrenia, the present study examined the relationship of psychometrically defined schizotypy with symptoms of depression and anxiety in a college student sample (n=1258). A series of confirmatory factor analyses indicated that a three-factor solution of positive schizotypy, negative schizotypy, and negative affect provided the best solution for self-report measures of schizotypy, anxiety, and depression. As hypothesized, the model indicated that symptoms of depression and anxiety are more strongly associated with the positive-symptom dimension of schizotypy than with the negative-symptom dimension. This is consistent with studies of schizophrenic patients and longitudinal findings that positive-symptom schizotypes are at risk for both mood and non-mood psychotic disorders, while negative-symptom schizotypes appear more specifically at risk for schizophrenia-spectrum disorders.

Impact of substance use on the onset and course of early psychosis

The strong comorbidity between psychosis and substance use is already identifiable in early psychosis, raising the question of the direction of the association between substance use and psychosis onset. It has long been considered that this association was explained by the self-medication hypothesis. This hypothesis has been recently challenged by several prospective studies carried out in population-based samples, showing a dose-response relationship between cannabis exposure and risk of psychosis. This association was independent from potential confounding factors such as exposure to other drugs and pre-existence of psychotic symptoms. As a large percentage of subjects from the general population is now exposed to this drug, even a small increase in the risk of adverse effects may have significant deleterious consequences for the health of the population. Hence, reducing exposure to cannabis may contribute to prevention of some incident cases of psychosis. Regarding prognosis, persistent substance misuse after the onset of psychosis has a deleterious impact on clinical outcome. Therapeutic programs for subjects with dual diagnosis should be implemented early in the course of psychosis to maximise their impact on the course of illness.

Schizotypy and mixed-handedness revisited

Although some previous studies assert that an association between schizotypy and loss of hand dominance is well established, the prevailing use of student populations, small effect sizes and arbitrariness of handedness classification suggest that this tentative association merits further investigation. The association of schizotypy and loss of hand dominance was examined using four samples. The first comprised 353 randomly selected individuals from the general community, the second comprised 131 screened volunteers participating as control subjects in a family study of schizophrenia, the third included 97 full siblings of schizophrenia patients, and the fourth consisted of 176 schizophrenia patients from the same study. The samples of screened volunteers and nonpsychotic siblings were used to replicate results from the community sample and to test the hypothesis that an increase in genetic liability is related to the association of schizotypal traits and mixed handedness. The results demonstrated that mixed handedness and schizotypy traits were unrelated in the representative sample from the community. This finding was replicated in the sample of screened volunteers, while siblings of schizophrenia patients showed a trend in the direction of the hypothesised relationship. In contrast, there was an expected significant but low in magnitude association between loss of hand dominance and the Schizotypal Personality Questionnaire factor of Cognitive Perceptual Dysfunction in schizophrenia patients.

Early adolescent cannabis exposure and positive and negative dimensions of psychosis

AIMS

To investigate the effect of exposure to cannabis early in adolescence on subclinical positive and negative symptoms of psychosis.

DESIGN

Cross-sectional survey in the context of an ongoing cohort study.

SETTING

Government-supported general population cohort study.

PARTICIPANTS

A total of 3500 representative 19-year olds in Greece.

MEASUREMENTS

Subjects filled in the 40-item Community Assessment of Psychic Experiences, measuring subclinical positive (paranoia, hallucinations, grandiosity, first-rank symptoms) and negative psychosis dimensions and depression. Drug use was also reported on.

FINDINGS

Use of cannabis was associated positively with both positive and negative dimensions of psychosis, independent of each other, and of depression. An association between cannabis and depression disappeared after adjustment for the negative psychosis dimensions. First use of cannabis below age 16 years was associated with a much stronger effect than first use after age 15 years, independent of life-time frequency of use. The association between cannabis and psychosis was not influenced by the distress associated with the experiences, indicating that self-medication may be an unlikely explanation for the entire association between cannabis and psychosis.

CONCLUSIONS

These results add credence to the hypothesis that cannabis contributes to the population level of expression of psychosis. In particular, exposure early in adolescence may increase the risk for the subclinical positive and negative dimensions of psychosis, but not for depression.

Agreement between self-rated and clinically assessed symptoms in subjects with psychosis

The aim of this study was to explore the capacity of acutely ill patients with psychosis (N = 40) to self-report their symptoms by comparing self-assessment and objective measures. Positive, negative, and depressive symptoms were rated using the Scale for the Assessment of Positive Symptoms, the Scale for the Assessment of Negative Symptoms, and the Calgary Depression Scale. Insight level was measured using the Scale to Assess Unawareness of Mental Disorder. Patients were asked to self-report positive, negative, and depressive symptoms using the Community Assessment of Psychic Experience. Patients presenting with acute psychotic disorders are able to assess fairly their positive, negative, and depressive symptoms. Significant associations were found between self-reported and objective measures of positive, negative, and depressive symptoms independently of insight level. Individual positive and negative symptoms were correctly self-assessed, except for persecutory delusion and alogia, respectively. These results suggest that self-report questionnaires can be used in educational programs to favor the patient's therapeutic adherence.

Nutritional intake of hazardous drinkers and dependent alcoholics in the UK

There are no recent assessments of nutritional intake in alcohol misusers in the United Kingdom. The purpose of this study was to measure nutritional intake in alcoholics attending an Alcohol Misuse outpatient clinic in an inner city general hospital in the United Kingdom and relating this to various measures of alcohol dependence. All patients (n = 30; 27 male, 3 female) consumed at least 100 g ethanol per day (mean 162 g/day) for at least 5 years and completed questionnaires on socio-demographics, alcohol dependency and psychosocial problems and had assays of biochemical and haematological indices. The data were analysed first with respect to the entire patient population and then according to the degree of alcohol dependency (mild, moderate or severe). The results showed that with respect to the entire patient group, one-third were below normal body weights, but one-quarter was overweight. The total energy intake (kJ/day) including alcohol was apparently adequate with respect to recommended levels in most patients. On average, approx. 60% of energy intake came from alcohol. The whole patient population had a low intake of one or more macro- and micro-nutrient compared to the dietary reference requirements. All patients had intakes of vitamin E and folate below UK recommended standards, while 85 - 95% of patients had low intakes of selenium and Vitamin D. Between 50 and 85% of all patents had intakes below UK recommended standards in calcium and zinc and Vitamins A, B(1), B(2), B(6) and C. There were significant correlations between calorie intake (when alcohol was excluded) and vitamins B(1), B(2), B(6) and C, and Ca, Mg, Fe and Zn intake. There were no correlations between alcohol intake with any of the nutritional and anthropometric variables or between the three subgroups with respect to daily energy, micro- and macro-nutrient intakes. In conclusion, malnutrition was common in this patient group: all subjects had intakes below UK recommended standards in one or more micro- or macro-nutrient. However, there was no difference in the degree of malnutrition between the harmful drinkers (mild dependency) and heavily dependent subgroups.