Tobacco, cannabis, and other illicit drug use among Finnish adolescent twins: causal relationship or correlated liabilities?

Serum brain-derived neurotrophic factor level and its relation with cannabis use disorder and schizophrenia: A cross-sectional exploratory study in patients at a tertiary care hospital

BACKGROUND

Brain-derived neurotrophic factor (BDNF) has considerable relevance in neural growth and differentiation. It has been evaluated as a biomarker for individuals with various psychiatric disorders such as substance-related disorders and psychotic disorders.

OBJECTIVE

The present study explored differences in the levels of BDNF (in serum) among subjects using cannabis (with and without schizophrenia).

METHODS

This cross-sectional observational study compared the serum BDNF level in male subjects aged 18-45 years. Four groups of 20 subjects each were included: individuals with tobacco use disorder only, patients having schizophrenia, patients with cannabis use disorder, and finally patients with comorbid cannabis use disorder and schizophrenia.

RESULTS

The BDNF levels were found to be significantly different across the four groups. The BDNF levels in subjects with concurrent schizophrenia and cannabis use disorder were higher than each of the other three groups (cannabis use disorder, schizophrenia, and tobacco use disorder only).

CONCLUSION

We find that BDNF may be higher when cannabis use disorder and schizophrenia co-occur, as compared to either of the conditions alone. The findings should be interpreted with caution due to the low sample size and potential confounders.

Limited psychological and social effects of lifetime cannabis use frequency: Evidence from a 30-year community study of 4,078 twins

BACKGROUND

Cannabis use is associated with outcomes like income, legal problems, and psychopathology. This finding rests largely on correlational research designs, which rely at best on statistical controls for confounding. Here, we control for unmeasured confounders using a longitudinal study of twins.

METHOD

In a sample of 4,078 American adult twins first assessed decades ago, we used cotwin control mixed effects models to evaluate the effect of lifetime average frequency of cannabis consumption measured on substance use, psychiatric, and psychosocial outcomes.

RESULTS

On average, participants had a lifetime cannabis frequency of about one to two times per month, across adolescence and adulthood. As expected, in individual-level analyses, cannabis use was significantly associated with almost all outcomes in the expected directions. However, when comparing each twin to their cotwin, which inherently controls for shared genes and environments, we observed within-pair differences consistent with possible causality in three of the 22 assessed outcomes: cannabis use disorder symptoms (βW-Pooled = .15, SE = .02, p = 1.7 × 10-22), frequency of tobacco use (βW-Pooled = .06, SE = .01, p = 1.2 × 10-5), and illicit drug involvement (βW-Pooled = .06, SE = .02, p = 1.2 × 10-4). Covariate specification curve analyses indicated that within-pair effects on tobacco and illicit drug use, but not cannabis use disorder, attenuated substantially when covarying for lifetime alcohol and tobacco use.

CONCLUSIONS

The cotwin control results suggest that more frequent cannabis use causes small increases in cannabis use disorder symptoms, approximately 1.3 symptoms when going from a once-a-year use to daily use. For other outcomes, our results are more consistent with familial confounding, at least in this community population of twins. (PsycInfo Database Record (c) 2023 APA, all rights reserved).

Cannabis Use in Physicians: A Systematic Review and Meta-Analysis

Background: Cannabis use by physicians can be detrimental for them and their patients. We conducted a systematic review and meta-analysis on the prevalence of cannabis use by medical doctors (MDs)/students. Method: PubMed, Cochrane, Embase, PsycInfo and ScienceDirect were searched for studies reporting cannabis use in MDs/students. For each frequency of use (lifetime/past year/past month/daily), we stratified a random effect meta-analysis depending on specialties, education level, continents, and periods of time, which were further compared using meta-regressions. Results: We included 54 studies with a total of 42,936 MDs/students: 20,267 MDs, 20,063 medical students, and 1976 residents. Overall, 37% had used cannabis at least once over their lifetime, 14% over the past year, 8% over the past month and 1.1 per thousand (‱) had a daily use. Medical students had a greater cannabis use than MDs over their lifetime (38% vs. 35%, p < 0.001), the past year (24% vs. 5%, p < 0.001), and the past month (10% vs. 2%, p < 0.05), without significance for daily use (0.5% vs. 0.05%, NS). Insufficient data precluded comparisons among medical specialties. MDs/students from Asian countries seemed to have the lowest cannabis use: 16% over their lifetime, 10% in the past year, 1% in the past month, and 0.4% daily. Regarding periods of time, cannabis use seems to follow a U-shape, with a high use before 1990, followed by a decrease between 1990 and 2005, and a rebound after 2005. Younger and male MDs/students had the highest cannabis use. Conclusions: If more than a third of MDs tried cannabis at least once in their lifetime, this means its daily use is low but not uncommon (1.1‱). Medical students are the biggest cannabis users. Despite being common worldwide, cannabis use is predominant in the West, with a rebound since 2005 making salient those public health interventions during the early stage of medical studies.

Familial associations in adolescent substance use disorder: a population-based cohort study

BACKGROUND AND AIMS

Family history of substance use disorder (SUD) affects a child's risk of the disorder through both genetic and shared environmental factors. We aimed to estimate the association between parental or older sibling SUD history with the risk of adolescent SUD diagnosis.

DESIGN, SETTING AND PARTICIPANTS

We conducted a population-based cohort study using administrative health-care databases in the Province of Manitoba, Canada, which has a universal and publicly funded health-care system. We included all children born from 1984 to 2000 who have linkages to both parents and were followed until age 18 years. We used generalized estimating equation models to produce unadjusted and adjusted relative risk (RR) estimates of adolescent SUD risk. The study cohort included 134 389 children and 31 307 full sibling pairs; 51.3% were male and 35.4% first-born.

MEASUREMENTS

The exposure was SUD diagnosis in a mother or father in either hospitalization or outpatient physician visit records before the children's age of 13 years. The secondary exposure was an adolescent SUD diagnosis in an older full sibling. The outcome was SUD diagnosis during adolescence (13 and 18 years of age) identified in either hospitalization or physician visit records. Children demographics and characteristics associated with SUD diagnosis were included in the models.

FINDINGS

Of the 134 389 children, 9.5% had a mother with a history of SUD, 11.3% had a father and 1.3% had an older sibling with a history of SUD diagnosis; 2566 (1.9%) had an adolescent SUD diagnosis. An increased risk of adolescent SUD was observed with SUD history in mothers [adjusted RR (aRR) = 2.50; 95% confidence interval (CI) = 2.26, 2.79], fathers (aRR = 2.15; 95% CI = 1.95, 2.37), both parents (aRR = 3.74; 95% CI = 3.24, 4.31) and older sibling (aRR = 3.85; 95% CI = 2.53, 5.87).

CONCLUSIONS

A family history of substance use disorder in parents or older siblings appears to be associated with increased SUD risk in adolescents.

Risk of pain disorders in offspring of parents with substance use disorders

AIMS

Individuals with substance use disorders (SUD) have higher risk of developing pain disorders. This study aimed to investigate the risk of major psychiatric disorders (MPD), SUD, and pain disorders among their offspring.

METHODS

This study used data from the Taiwan National Health Research Database. The case cohort included participants who had a parent diagnosed with SUD. The matched control cohort was offspring of parents without any SUD or major psychiatric disorder (MPD). Poisson regression was applied to estimate the risk of MPD, SUD, and pain disorder between case and control cohorts.

RESULTS

We recruited 13,840 cases and 138,400 matched controls. After adjusting for demographic characteristics and family history of psychiatric disorder, the offspring of parents with SUD had higher risk for bipolar disorder (reported as risk ratio with 95% confidence interval: 2.48, 1.79-3.43), depressive disorder (2.22, 1.94-2.52), SUD (2.53, 2.18-2.92), and alcohol use disorder (1.43, 1.16-1.76) than controls. With adjustments of demographic characteristics, individual MPD, and family history of psychiatric disorder, they also presented higher risk than controls for several pain disorders, including migraine (1.43, 1.15-1.78), fibromyalgia (1.21, 1.03-1.42), dorsopathies (1.20, 1.06-1.37), dysmenorrhea (1.16, 1.04-1.29), irritable bowel syndrome (1.26, 1.11-1.43), and dyspepsia (1.14, 1.02-1.27).

CONCLUSIONS

Clinicians should be aware of the influence of parental SUD on the elevated risk for MPD, SUD, and pain disorders in their offspring.

Association between platelet MAO activity and lifetime drug use in a longitudinal birth cohort study

RATIONALE

Platelet monoamine oxidase (MAO) activity, a marker of central serotonergic capacity, has been associated with a variety of problem behaviours. However, studies on platelet MAO activity and addictive drugs have not consistently linked MAO activity with addiction or reported to predict illicit substance use initiation or frequency.

OBJECTIVES

Platelet MAO activity and illicit drug use was examined in a longitudinal birth cohort study.

METHODS

The sample included both birth cohorts (original n = 1238) of the Estonian Children Personality Behaviour and Health Study. Longitudinal association from age 15 to 25 years between platelet MAO activity and lifetime drug use was analysed by mixed-effects regression models. Differences at ages 15, 18 and 25 were analysed by t-test. Cox proportional hazard regression analysis was used to assess the association between platelet MAO activity and the age of drug use initiation.

RESULTS

Male subjects who reported at least one drug use event had lower platelet MAO activity compared to nonusers, both in cross-sectional and longitudinal analyses. Males with low platelet MAO activity had started to use drugs at a younger age. Moreover, in male subjects who had experimented with illicit drugs only once in lifetime, low platelet MAO activity was also associated with higher risk at a younger age. In females, platelet MAO activity was not associated with drug use.

CONCLUSION

In males, low platelet MAO activity is associated with drug abuse primarily owing to risk-taking at early age.

Cigarette Smoking Behavior a Gateway to Opium Use Disorder: A Mendelian Randomization Analysis

Gateway hypothesis presumes that using a psychotropic drug can increase the probability of using another drug. The study was to assess whether cigarette smoking is a gateway drug for subsequent opium use. Mendelian randomization (MR) analysis was applied to test and estimate the size of causal effect of cigarette smoking on opium use. The CHRNA3 rs1051730 polymorphism was used as an instrumental variable. A population-based case control study in the setting of Fasa Cohort Study was carried out using 477 cases and 531 controls based on their opium use status at the baseline of cohort study. The logistic two stage estimator method was applied. The Number of cigarettes smoked per day was associated with opium use (OR 1.17, 95% CI 1.15-1.19). In the MR analysis, rs1051730 T alleles were associated with increased risk of opium use among ever smokers (OR 5.73, 95% CI 1.72-19.07) however there found no evidence of association among never smokers. In instrumental variable analysis, showed that on average smoking every 1 more cigarette per day increases the odds of opium use by 1.17 (OR 1.17, 95%CI:1.14-1.19). The MR analysis found a positive finding on the relationship between cigarette smoking and opium use which supports the gateway hypothesis. It adds new information to the gateway theory regarding the relation of cigarette smoking and drug use, and increases our understanding of the importance of tobacco control for prevention of opium addiction.

Alcohol Use Disorder Symptoms Rather than Alcohol Exposure Predict Experiences of Cannabis Use Disorder Symptoms among Adolescents and Young Adults

Background: Alcohol and cannabis use are highly comorbid. Objective: We evaluate if alcohol use and/or alcohol use disorder symptoms predict experiences of cannabis use disorder symptoms among adolescents and young adults and whether the relationships differ based on frequency of cannabis use, recency of cannabis initiation and age. Method: Data were drawn from five annual surveys of the National Survey on Drug Use and Health (2014-2018) to include adolescents and young adults (age 12 to 21 years) who reported using cannabis and alcohol at least once in the past 30 days. Results: Number of alcohol use disorder symptoms, over and above alcohol quantity or frequency, was positively associated with each of the cannabis use disorder symptoms as well as the total number of cannabis use disorder symptoms endorsed. The association between alcohol and cannabis use disorder symptoms was stronger among those who were younger and those who initiated cannabis use within the past 2 years. Conclusions: Treatment should consider these and other cross-over effects of substance disorder symptoms when addressing risk for chronic and dependent use.

Cigarette smoke exposure has region-specific effects on GDAP1 expression in mouse hippocampus

Early detection markers for substance use disorders are urgently needed. Recently, an association between the methylation of Ganglioside-induced differentiation-associated protein 1 (GDAP1) and alcohol addiction was found in a US and German population. In this study, we investigate whether GDAP1 expression might be affected by cigarette smoke as well and thus might be a marker of substance addiction in general. 11 adult female C57BL/6 J mice (6 wildtype and 5 lacking the NO-sensitive guanylyl cyclase1 (NO-GC1 KO)) were exposed to cigarette smoke over a period of 5 weeks, their brains immunohistochemically stained and compared to 11 non exposed mice (5 WT and 6 KO). The deletion of NO-GC1 results in a complete loss of synaptic plasticity, therefore, addiction-related alterations might become more obvious. Co-staining of anti-GDAP1 and DAPI revealed protein in the stratum granulare of the hippocampus. Three randomized frames for dentate gyrus (DG) and three for Cornu Ammonis region 1 (CA1) were used to count GDAP1. Cigarette smoke exposure significantly influenced GDAP1 expression depending on the hippocampal region but was not influenced by guanyl cyclase. In conclusion, cigarette smoke exposure alone had an effect on GDAP1 amount in both regions. Therewith, GDAP1might be a biomarker for substance addiction in general.

Acute Nicotine Exposure Alters Ventral Tegmental Area Inhibitory Transmission and Promotes Diazepam Consumption

Nicotine use increases the risk for subsequent abuse of other addictive drugs, but the biological basis underlying this risk remains largely unknown. Interactions between nicotine and other drugs of abuse may arise from nicotine-induced neural adaptations in the mesolimbic dopamine (DA) system, a common pathway for the reinforcing effects of many addictive substances. Previous work identified nicotine-induced neuroadaptations that alter inhibitory transmission in the ventral tegmental area (VTA). Here, we test whether nicotine-induced dysregulation of GABAergic signaling within the VTA increases the vulnerability for benzodiazepine abuse that has been reported in smokers. We demonstrate in rats that nicotine exposure dysregulates diazepam-induced inhibition of VTA GABA neurons and increases diazepam consumption. In VTA GABA neurons, nicotine impaired KCC2-mediated chloride extrusion, depolarized the GABAA reversal potential, and shifted the pharmacological effect of diazepam on GABA neurons from inhibition toward excitation. In parallel, nicotine-related alterations in GABA signaling observed ex vivo were associated with enhanced diazepam-induced inhibition of lateral VTA DA neurons in vivo Targeting KCC2 with the agonist CLP290 normalized diazepam-induced effects on VTA GABA transmission and reduced diazepam consumption following nicotine administration to the control level. Together, our results provide insights into midbrain circuit alterations resulting from nicotine exposure that contribute to the abuse of other drugs, such as benzodiazepines.

Is E-cigarette use a gateway to marijuana use? Longitudinal examinations of initiation, reinitiation, and persistence of e-cigarette and marijuana use

BACKGROUND

Concerns have been raised regarding e-cigarette use as a potential stepping-stone to marijuana use. Based on Kandel's gateway hypothesis, this study investigated if e-cigarette use could lead to marijuana use by testing two hypotheses with a longitudinal national U.S. adult sample, including (1) primary hypothesis: e-cigarette use is a gateway to marijuana use; and (2) falsification hypothesis: marijuana use is not a gateway to e-cigarette use.

METHODS

Adults were extracted from the Population Assessment of Tobacco and Health Study Waves 1-3 (2013-2016). For primary hypotheses, based on baseline e-cigarette use statuses, three study groups were defined, and three logistic regressions were conducted to examine associations between baseline e-cigarette use and follow-up marijuana use initiation, reinitiation, and persistence, respectively. Similarly, for falsification hypotheses, three additional study groups were defined, and three logistic regressions were conducted to examine associations between baseline marijuana use and follow-up e-cigarette use behaviors.

RESULTS

Baseline e-cigarette use was associated with marijuana use initiation and reinitiation (ORs = 2.08, 1.37, respectively, both ps < .05) but not persistence at follow-up. Additionally, baseline marijuana use was associated with only e-cigarette use initiation (OR = 2.23, p < .01) but not reinitiation or persistence at follow-up.

CONCLUSIONS

Findings partially support the gateway hypothesis that e-cigarette use could be a steppingstone to marijuana use reinitiation among the U.S. adults. The mechanisms and behavioral characteristics, such as etiological and psychosocial factors, that may pertain to the progression from e-cigarette use to reinitiation of other substance use should be further investigated to inform effective behavioral, educational, and policy interventions.

Adolescent Externalizing Psychopathology and Its Prospective Relationship to Marijuana Use Development from Age 14 to 30: Replication Across Independent Longitudinal Twin Samples

Externalizing psychopathology in early adolescence is a highly heritable risk factor for drug use, yet how it relates to marijuana use development is not well-characterized. We evaluate this issue in independent twin samples from Colorado (N = 2608) and Minnesota (N = 3630), assessed from adolescence to early adulthood. We used a biometric latent growth model of marijuana use frequency with data from up to five waves of assessment from ages 14 to 30, to examine change in marijuana use and its relationship with a factor model of adolescent externalizing psychopathology. The factor structure of adolescent externalizing psychopathology was similar across samples, as was the association between that common factor and early marijuana use (Minnesota r = 0.67 [0.60, 0.75]; Colorado r = 0.69 [0.59, 0.78]), and increase in use (Minnesota r = 0.18 [0.10, 0.26]; Colorado r = 0.20 [0.07, 0.34]). Early use was moderately heritable in both samples (Minnesota h² = 0.57 [0.37, 0.79]; Colorado h² = 0.42 [0.14, 0.73]). Increase in use was highly heritable in Minnesota (h² = 0.82 [0.72, 0.88]), less so in Colorado (h² = 0.22 [0.01, 0.66]), and shared environmental effects were larger in Colorado (c² = 0.55 [0.14, 0.83]) than Minnesota (c² = 0 [0, 0.06]). We found moderate genetic correlations between externalizing psychopathology and early use in both samples. Finally, additional analyses in the Minnesota sample indicated that marijuana use decreased during the late 20s. This decline is strongly heritable (h² = 0.73 [0.49, 0.91]) and moderately negatively correlated with adolescent externalizing psychopathology (r = - 0.41 [- 0.54, - 0.28]). Adolescent externalizing psychopathology is genetically correlated with change in late adolescent marijuana use (late teens, early 20s), as well as maintenance of use in early adulthood (late 20 s) even after controlling for the effects of early use.

FinnTwin12 Cohort: An Updated Review

This review offers an update on research conducted with FinnTwin12 (FT12), the youngest of the three Finnish Twin Cohorts. FT12 was designed as a two-stage study. In the first stage, we conducted multiwave questionnaire research enrolling all eligible twins born in Finland during 1983-1987 along with their biological parents. In stage 2, we intensively studied a subset of these twins with in-school assessments at age 12 and semistructured poly-diagnostic interviews at age 14. At baseline, parents of intensively studied twins were administered the adult version of the interview. Laboratory studies with repeat interviews, neuropsychological tests, and collection of DNA were made of intensively studied twins during follow-up in early adulthood. The basic aim of the FT12 study design was to obtain information on individual, familial and school/neighborhood risks for substance use/abuse prior to the onset of regular tobacco and alcohol use and then track trajectories of use and abuse and their consequences into adulthood. But the longitudinal assessments were not narrowly limited to this basic aim, and with multiwave, multirater assessments from ages 11 to 12, the study has created a richly informative data set for analyses of gene-environment interactions of both candidate genes and genomewide measures with measured risk-relevant environments. Because 25 years have elapsed since the start of the study, we are planning a fifth-wave follow-up assessment.

Nicotine Gateway Effects on Adolescent Substance Use

Given the rise in teenage use of electronic nicotine delivery systems ("vaping") in congruence with the increasing numbers of drug-related emergencies, it is critical to expand the knowledge of the physical and behavioral risks associated with developmental nicotine exposure. A further understanding of the molecular and neurochemical underpinnings of nicotine's gateway effects allows emergency clinicians to advise patients and families and adjust treatment accordingly, which may minimize the use of tobacco, nicotine, and future substances. Currently, the growing use of tobacco products and electronic cigarettes among teenagers represents a major public health concern. Adolescent exposure to tobacco or nicotine can lead to subsequent abuse of nicotine and other substances, which is known as the gateway hypothesis. Adolescence is a developmentally sensitive time period when risk-taking behaviors, such as sensation seeking and drug experimentation, often begin. These hallmark behaviors of adolescence are largely due to maturational changes in the brain. The developing brain is particularly vulnerable to the harmful effects of drugs of abuse, including tobacco and nicotine products, which activate nicotinic acetylcholine receptors (nAChRs). Disruption of nAChR development with early nicotine use may influence the function and pharmacology of the receptor subunits and alter the release of reward-related neurotransmitters, including acetylcholine, dopamine, GABA, serotonin, and glutamate. In this review, we emphasize that the effects of nicotine are highly dependent on timing of exposure, with a dynamic interaction of nAChRs with dopaminergic, endocannabinoid, and opioidergic systems to enhance general drug reward and reinforcement. We analyzed available literature regarding adolescent substance use and nicotine's impact on the developing brain and behavior using the electronic databases of PubMed and Google Scholar for articles published in English between January 1968 and November 2018. We present a large collection of clinical and preclinical evidence that adolescent nicotine exposure influences long-term molecular, biochemical, and functional changes in the brain that encourage subsequent drug abuse.

Latrophilins: A Neuro-Centric View of an Evolutionary Conserved Adhesion G Protein-Coupled Receptor Subfamily

The adhesion G protein-coupled receptors latrophilins have been in the limelight for more than 20 years since their discovery as calcium-independent receptors for α-latrotoxin, a spider venom toxin with potent activity directed at neurotransmitter release from a variety of synapse types. Latrophilins are highly expressed in the nervous system. Although a substantial amount of studies has been conducted to describe the role of latrophilins in the toxin-mediated action, the recent identification of endogenous ligands for these receptors helped confirm their function as mediators of adhesion events. Here we hypothesize a role for latrophilins in inter-neuronal contacts and the formation of neuronal networks and we review the most recent information on their role in neurons. We explore molecular, cellular and behavioral aspects related to latrophilin adhesion function in mice, zebrafish, Drosophila melanogaster and Caenorhabditis elegans, in physiological and pathophysiological conditions, including autism spectrum, bipolar, attention deficit and hyperactivity and substance use disorders.

Association between tobacco smoking and opioid use: A meta-analysis

BACKGROUND

Tobacco smoking has been shown to be a major risk factor for opioid use and opioid use disorders in several observational studies; however, the results are inconsistent. Thus, this systematic review and meta-analysis of observational studies was conducted to investigate the association between smoking behavior and opioid use and opioid use disorders.

METHODS

A systematic literature search of relevant keywords was done in Medline, Embase, Scopus, Web of Science, and Google Scholar up to October 2017. The reference lists of retrieved articles were also examined for inclusion. While random effects meta-analysis was used, pooled odds ratio (OR) and 95% confidence intervals were calculated using Der-Simonian and Laird method, taking into account conceptual heterogeneity. Subgroup analyses were performed using participants and studies' characteristics to assess the sources of heterogeneity.

RESULTS

Ten eligible observational studies (6 cohorts and 4 population-based cross sectional studies), with 175,063 participants, were identified. The pooled OR of opioid use disorders was 8.23 (95% CI: 3.07-22.09) for current smokers compared to nonsmokers; pooled OR for opioid use was 2.51 (95% CI: 1.91-3.28). Opioid use or opioid use disorders were positively associated with earlier age at onset of smoking (pooled OR = 1.66; 95% CI: 1.28-2.16).

CONCLUSIONS

The results of this meta-analysis confirmed that tobacco smoking is associated with opioid use and opioid use disorders development. This conclusion has an important public health message for areas with high smoking prevalence and high opioid use and opioid use disorders incidence.

Association between polygenic risk for tobacco or alcohol consumption and liability to licit and illicit substance use in young Australian adults

BACKGROUND

Co-morbid substance use is very common. Despite a historical focus using genetic epidemiology to investigate comorbid substance use and misuse, few studies have examined substance-substance associations using polygenic risk score (PRS) methods.

METHODS

Using summary statistics from the largest substance use GWAS to date (258,797- 632,802 subjects), GWAS and Sequencing Consortium of Alcohol and Nicotine use (GSCAN), we constructed PRSs for smoking initiation (PRS-SI), age of initiation of regular smoking (PRS-AI), cigarettes per day (PRS-CPD), smoking cessation (PRS-SC), and drinks per week (PRS-DPW). We then estimated the fixed effect of individual PRSs on 22 lifetime substance use and substance use disorder phenotypes collected in an independent sample of 2463 young Australian adults using genetic restricted maximal likelihood (GREML) in Genome-wide Complex Trait Analysis (GCTA), separately in females, males and both sexes together.

RESULTS

After accounting for multiple testing, PRS-SI significantly explained variation in the risk of cocaine (0.67%), amphetamine (1.54%), hallucinogens (0.72%), ecstasy (1.66%) and cannabis initiation (0.97%), as well as DSM-5 alcohol use disorder (0.72%). PRS-DPW explained 0.75%, 0.59% and 0.90% of the variation of cocaine, amphetamine and ecstasy initiation respectively. None of the 22 phenotypes including emergent classes of substance use were significantly predicted by PRS-AI, PRS-CPD, and PRS-SC.

CONCLUSIONS

To our knowledge, this is the first study to report significant genetic overlap between the polygenic risks for smoking initiation and alcohol consumption and the risk of initiating major classes of illicit substances. PRSs constructed from large discovery GWASs allows the detection of novel genetic associations.

Predictors of initiation of nicotine, alcohol, cannabis, and cocaine use: Results of the National Epidemiologic Survey on Alcohol and Related Conditions (NESARC)

BACKGROUND AND OBJECTIVES

There may be substantial overlap in the risk factors for substance use and substance use disorders (SUD). Identifying risk factors for substance use initiation is essential for understanding the etiology and natural history of SUD and to develop empirically-based preventive interventions to reduce initiation.

METHODS

Analyses were done on Wave 1 participants of the National Epidemiological Survey of Alcohol and Related Conditions (NESARC) (n = 43,093). Estimates of the cumulative probability of substance use initiation were obtained separately for nicotine, alcohol, cannabis, and cocaine. Survival analyses with time-varying covariates were implemented to identify risk factors for substance initiation.

RESULTS

The lifetime cumulative probabilities of substance initiation were 45.5% for nicotine, 82% for alcohol, 19.6% for cannabis, and 6.4% for cocaine. Among respondents with lifetime nicotine use, 50% had used it by age 15.3, whereas for alcohol, cannabis, and cocaine the respective ages were 17.8, 16.6, and 19.8. Previous use of another substance, being male, having a cluster B personality disorder, family history of SUD, and being separated, divorced, or widowed increased the risk of use of all the substances assessed, whereas social anxiety disorder and some personality disorders were associated with specific substances.

DISCUSSION AND CONCLUSIONS

Although the age of substance use initiation varies by substance, in more than 50% of cases initiation of use occurs in the first two decades of life. Although most risk factors for substance use initiation are common across substances, some are substance-specific.

SCIENTIFIC SIGNIFICANCE

This information may help in the development of empirically-based preventive interventions. (Am J Addict 2018;27:477-484).

Drug use among youth: National survey data support a common liability of all drug use

The prevalence of substance use disorders in adults is higher if substance use is initiated during adolescence, underscoring the importance of youth substance use prevention. We examined whether the use of one substance by adolescents is associated with increased risk for using any other substance, regardless of use sequences. In 2017 we examined data from 17,000 youth aged 12-17 who participated in the 2014 National Survey on Drug Use and Health, a sample of nationally representative data on substance use among the U.S. civilian, noninstitutionalized population aged 12 or older. Descriptive analyses and multivariable logistic regression models were applied. After controlling for age, sex, and race/ethnicity, compared with youth without past-month marijuana use, youth with past-month marijuana use were 8.9 times more likely to report past-month cigarette use, 5.6, 7.9 and 15.8 times more likely to report past-month alcohol use, binge use, or heavy use (respectively), and 9.9 times more likely to report past-month use of other illicit drugs. The prevalence of past-month use of cigarettes, marijuana, and other illicit drugs was significantly higher among past-month alcohol users compared with youth without past-month alcohol use, and increased as intensity of alcohol use rose. Among past-month cigarette smokers, the prevalence of marijuana, other illicit drugs, and alcohol use were each significantly higher than youth without past-month cigarette use. Youth marijuana use, cigarette smoking, or alcohol consumption is associated with other substance use. This finding has importance for youth prevention, supporting a message no use by youth of any substance.

Nicotine dependence predicts cannabis use disorder symptoms among adolescents and young adults

PURPOSE

We evaluate if cigarette smoking and/or nicotine dependence predicts cannabis use disorder symptoms among adolescent and young adult cannabis users and whether the relationships differ based on frequency of cannabis use.

METHODS

Data were drawn from seven annual surveys of the NSDUH to include adolescents and young adults (age 12-21) who reported using cannabis at least once in the past 30 days (n = 21,928). Cannabis use frequency trends in the association between cigarette smoking, nicotine dependence and cannabis use disorder symptoms were assessed using Varying Coefficient Models (VCM's).

RESULTS

Over half of current cannabis users also smoked cigarettes in the past 30 days (54.7% SE 0.48). Cigarette smoking in the past 30 days was associated with earlier onset of cannabis use, more frequent cannabis use and a larger number of cannabis use disorder symptoms compared to those who did not smoke cigarettes. After statistical control for socio-demographic characteristics and other substance use behaviors, nicotine dependence but not cigarette smoking quantity or frequency was positively and significantly associated with each of the cannabis use disorder symptoms as well as the total number of cannabis symptoms endorsed. Higher nicotine dependence scores were consistently associated with the cannabis use disorder symptoms across all levels of cannabis use from 1 day used (past month) to daily cannabis use, though the relationship was strongest among infrequent cannabis users.

CONCLUSION

Prevention and treatment efforts should consider cigarette smoking comorbidity when addressing the increasing proportion of the US population that uses cannabis.

The genetic epidemiology of substance use disorder: A review

BACKGROUND

Substance use disorder (SUD) remains a significant public health issue. A greater understanding of how genes and environment interact to regulate phenotypes comprising SUD will facilitate directed treatments and prevention.

METHODS

The literature studying the neurobiological correlates of SUD with a focus on the genetic and environmental influences underlying these mechanisms was reviewed. Results from twin/family, human genetic association, gene-environment interaction, epigenetic literature, phenome-wide association studies are summarized for alcohol, nicotine, cannabinoids, cocaine, and opioids.

RESULTS

There are substantial genetic influences on SUD that are expected to influence multiple neurotransmission pathways, and these influences are particularly important within the dopaminergic system. Genetic influences involved in other aspects of SUD etiology including drug processing and metabolism are also identified. Studies of gene-environment interaction emphasize the importance of environmental context in SUD. Epigenetic studies indicate drug-specific changes in gene expression as well as differences in gene expression related to the use of multiple substances. Further, gene expression is expected to differ by stage of SUD such as substance initiation versus chronic substance use. While a substantial literature has developed for alcohol and nicotine use disorders, there is comparatively less information for other commonly abused substances.

CONCLUSIONS

A better understanding of genetically-mediated mechanisms involved in the neurobiology of SUD provides increased opportunity to develop behavioral and biologically based treatment and prevention of SUD.

National Trends in Substance Use and Use Disorders Among Youth

OBJECTIVE

To examine trends in the 12-month prevalence of patterns of substance use and substance use disorders (SUDs) among US youth during 2002 through 2014.

METHOD

Data were from 288,300 persons 12 to 17 years old who participated in the 2002 to 2014 National Surveys on Drug Use and Health. Descriptive analyses and bivariable and multivariable logistic regressions were applied.

RESULTS

During 2002 through 2014, among US youth, the 12-month prevalence of any substance use decreased by 27.1% (from 43.2% to 31.5%); among youth users, the 12-month prevalence of SUDs decreased by 28.9% (from 27.0% to 19.2%), and the ratio of substance dependence to abuse decreased from 2.2 to 1.6. Multiple substance use was common and was associated with SUDs. During 2002 through 2014, the prevalence of using marijuana and alcohol only, using marijuana only, and having marijuana use disorders only increased, whereas most other trends were downward. Increases in age at first substance use were associated with downward trends in any substance use. Upward trends in age at first substance use, youth and parental strong disapproval of cigarette use, and youths' seatbelt-wearing prevalence and downward trends in substance use patterns were associated with the downward trend in SUDs among youth users.

CONCLUSION

The 12-month prevalence of any substance use among youth and SUDs among youth users decreased during 2002 through 2014. Postponing age at first use of any substance is critical among youth in the United States. Future research is needed to better understand the interrelations between specific risk and protective factors, age at first substance use, substance use patterns, and SUDs among youth users.

Young adults report increased pleasure from smoking cigarettes when drinking alcohol but not when using marijuana

BACKGROUND

Among young adults, cigarette smoking is strongly associated with alcohol and marijuana use. The present study compared self-reported co-use of cigarettes and alcohol versus cigarettes and marijuana among young adults using cross-sectional survey data.

METHODS

Participants were young adult cigarette smokers (age 18 to 25) who also reported past month alcohol or marijuana use enrolled in a randomized trial testing a smoking cessation intervention on Facebook. Participants self-reported extent of cigarette smoking under the influence of alcohol or marijuana and differences in perceived pleasure from cigarette smoking when drinking alcohol compared to using marijuana.

RESULTS

Among cigarette smokers who drank alcohol and used marijuana in the past month (n=200), a similar percentage of cigarettes were smoked under the influence of alcohol (42.4%±31.2%) and marijuana (43.1% ±30.0%). Among alcohol + marijuana users, perceived pleasure from smoking cigarettes was significantly greater when drinking alcohol versus when using marijuana (t₍₁₉₉₎=7.05, p<0.001). There was, on average, an increase in perceived pleasure from smoking cigarettes when drinking alcohol, though perceived pleasure did not differ by binge drinking frequency. In contrast, there was on average no change in perceived pleasure from smoking cigarettes when using marijuana. Results from the cigarette smokers who used alcohol + marijuana were similar to cigarette smokers who only used alcohol (n=158) or only used marijuana (n=54).

CONCLUSION

Findings highlight greater perceived reward from smoking cigarettes when drinking alcohol compared to when using marijuana, informing smoking cessation interventions that target users of multiple substances.

Progression in substance use initiation: A multilevel discordant monozygotic twin design

Considerable attention has been paid to the "gateway" pattern of drug use initiation in which individuals progress from tobacco and alcohol use to cannabis and other illicit drugs. The extent to which this sequence reflects a causal impact of licit substance use on illicit substance involvement remains unclear. Clarifying the mechanisms underlying substance use initiation may help inform our understanding of risk for psychopathology, as increasing research is demonstrating associations between initiation patterns and heavier involvement. This study examined patterns of substance use initiation using a discordant twin design. Participants were 3,476 monozygotic twins (37% male) from the Australian Twin Registry who reported on their ages of tobacco, alcohol, and cannabis initiation. Multilevel proportional hazard regression models were used to (a) estimate within-twin-pair and between-twin-pair contributions to associations between the ages of onset of different drugs; and (b) examine whether the magnitude of effects differed as a function of the order of substance use initiation. Finding significant effects within twin pairs would support the hypothesis that the age of initiation of a substance causally influences the age of initiation of a subsequent substance. Finding significant effects between twin pairs would support the operation of familial influences that explain variation in the ages of initiation of multiple drugs. Within-twin-pair effects for typical patterns were modest. When initiation was atypical, however, larger within-twin-pair effects were observed and causal influences were more strongly implicated. Results support the utility of examining the timing and ordering of substance use initiation within sophisticated, genetically informative designs.

Psychosocial Factors Associated With Smoking Intention in Korean Male Middle School Students

This study examined psychosocial factors influencing smoking intention in Korean male middle school students. We used a descriptive cross-sectional design, based on the biopsychosocial model, to analyze data from 309 male adolescents aged 14–16 years in middle school. Of the psychological factors examined, stress and risk-taking tendency were significantly associated with smoking intention. Of the social factors examined, social normative beliefs, close friends’ and siblings’ smoking, and low socioeconomic status were significant factors in smoking intention. The explanatory power of these variables in the predictive model was 23.1%. In conclusion, the unique psychological and social characteristics of adolescents should be reflected in interventions for smoking prevention.

Birth Cohorts Analysis of Adolescent Cigarette Smoking and Subsequent Marijuana and Cocaine Use

OBJECTIVES

To examine whether the drug behavior of adults from different birth cohorts is shaped by adolescent drug experiences and whether adult prevalence of marijuana and cocaine use depends on adolescent cigarette or alcohol use prevalence.

METHODS

We analyzed 18 birth cohorts comprising 8th, 10th, and 12th graders, sampled from 1991 to 2008, from Monitoring the Future, an annual nationally representative cross-sectional survey of high school students in the United States (n = 864 443).

RESULTS

Within cohorts, lifetime rates of 8th and 10th grade cigarette use were significantly associated with subsequent lifetime rates of marijuana and cocaine use, controlling for trends in use and social norms toward drug use. Each percent increase (or decrease) in 8th and 10th grade smoking was associated with an 8% increase (or decrease) in prevalence of later marijuana use and 14% to 23% increase (or decrease) in prevalence of later cocaine use. Relationships were consistent by gender and race/ethnicity.

CONCLUSIONS

Prevalences of smoking in 8th and 10th grade and of marijuana and cocaine use in 12th grade are associated. Public health campaigns should focus on early stages of adolescence, when drug use habits are forming.

Developmental Changes in Genetic and Shared Environmental Contributions to Smoking Initiation and Subsequent Smoking Quantity in Adolescence and Young Adulthood

BACKGROUND

Few studies examining the genetic architecture of cigarette smoking have focused on adolescents or examined developmental changes in additive genetic, shared environment, and unique environmental influences on liability to initiate cigarette smoking and quantity of cigarettes smoked. The aim of this study was to add to the literature on liability to initiate and use cigarettes during adolescence using a nationally representative sample.

METHOD

Data for this study came from adolescent and young adult twin pairs (aged 14-33 years) from the National Longitudinal Study of Adolescent to Adult Health. We ran a series of developmental causal-contingent-common pathway models to examine whether additive genetic, shared, and unique environmental influences on liability to the initiation of cigarette use are shared with those on smoking quantity, and whether their contributions change across development.

RESULTS

We found evidence for a developmental shift in genetic and shared environmental contributions to cigarette use. Early in adolescence, genetic and environmental influences work independently on liability to cigarette smoking initiation and quantity of cigarettes smoked, but liability to these behaviors becomes correlated as individuals age into young adulthood.

CONCLUSIONS

These findings provide insight into the causal processes underlying the liability to smoke cigarettes. With age, there is greater overlap in the genetic and environmental factors that influence the initiation of cigarette smoking and quantity of cigarettes smoked.

Investigating Progression in Substance Use Initiation Using a Discrete-Time Multiple Event Process Survival Mixture (MEPSUM) Approach

The order and timing of substance initiation has significant implications for later problematic patterns of use. Despite the need to study initiation from a multivariate framework, survival analytic methods typically cannot accommodate more than two substances in one model. The Discrete-Time Multiple Event Process Survival Mixture (MEPSUM; Dean, Bauer, & Shanahan, 2014) model represents an advance by incorporating more than two outcomes and enabling establishment of latent classes within a multivariate hazard distribution. Employing a MEPSUM approach, we evaluated patterns of tobacco, alcohol, and cannabis initiation in the National Longitudinal Study of Adolescent to Adult Health (N=18,923). We found four classes that differed in their ages and ordering of peak initiation risk. Demographics, externalizing psychopathology, and personality significantly predicted class membership. Sex differences in the association between delinquency and initiation patterns also emerged. Findings support the utility of the MEPSUM approach in elucidating developmental pathways underlying clinically relevant phenomena.

Are genetic variants for tobacco smoking associated with cannabis involvement?

BACKGROUND

Cannabis users are highly likely to also be tobacco cigarette smokers and a proportion of this comorbidity is attributable to shared genetic influences. Three large meta-analyses of genomewide association studies (GWAS) of tobacco smoking have identified multiple genomewide significant (p<5×10(-8)) single nucleotide polymorphisms (SNPs). We examine whether these SNPs are associated with tobacco smoking and with cannabis involvement in an independent sample.

METHOD

Eleven SNPs associated with cigarettes per day (CPD), ever versus never smoking and current smoking/smoking cessation at p<5×10(-8) were selected from three published meta-analyses. Association analyses were conducted with similar tobacco smoking measures in 2716 European-American subjects from the Study of Addictions Genes and Environment (SAGE) and with lifetime and current cannabis use and DSM-IV cannabis abuse/dependence.

RESULTS

Cannabis use and tobacco smoking correlated at 0.54. Rs16969968 in CHRNA5 (and its proxy, rs1051730 in CHRNA3) and rs1451240, a proxy for rs13280604 in CHRNB3, were associated with CPD after Bonferroni correction (p<0.006). rs1451240 was also associated with DSM-IV cannabis abuse/dependence. Rs6265 in BDNF was associated with smoking initiation, as in the original meta-analysis and also with lifetime cannabis use. Associations with cannabis involvement were no longer significant upon adjustment for the tobacco smoking measures.

CONCLUSIONS

The modest associations between cannabis involvement and SNPs for tobacco smoking were not independent of the comorbidity between tobacco and cannabis involvement. Larger samples of individuals might be required to articulate the specific genetic architecture of cannabis involvement.

The Gateway Hypothesis of substance abuse: developmental, biological and societal perspectives

The Gateway Hypothesis describes how tobacco or alcohol use precedes marijuana and other illicit drug use. We review the epidemiological data, explore the underlying molecular mechanisms in mice and discuss the societal implications of the hypothesis, including the use of e-cigarettes by young people.

CONCLUSION

Our mouse model identifies biological processes underlying the hypothesis, showing that nicotine is a gateway drug that exerts a priming effect on cocaine through increased global acetylation in the striatum.

Cannabis and psychosis: Neurobiology

Cannabis is a known risk factor for schizophrenia, although the exact neurobiological process through which the effects on psychosis occur is not well-understood. In this review, we attempt to develop and discuss a possible pathway for the development of psychosis. We examine the neurobiological changes due to cannabis to see if these changes are similar to those seen in schizophrenic patients the findings show similarities; however, these mere similarities cannot establish a 'cause-effect' relationship as a number of people with similar changes do not develop schizophrenia. Therefore, the 'transition-to-psychosis' due to cannabis, despite being a strong risk factor, remains uncertain based upon neurobiological changes. It appears that other multiple factors might be involved in these processes which are beyond neurobiological factors. Major advances have been made in understanding the underpinning of marijuana dependence, and the role of the cannabinoid system, which is a major area for targeting medications to treat marijuana withdrawal and dependence, as well as other addictions is of now, it is clear that some of the similarities in the neurobiology of cannabis and schizophrenia may indicate a mechanism for the development of psychosis, but its trajectories are undetermined.

Is the relationship between early-onset cannabis use and educational attainment causal or due to common liability?

BACKGROUND

Several studies have shown that early cannabis use is correlated with poor educational performance including high school drop-out. The predominant explanation for this relationship is that cannabis use causes disengagement from education. Another explanation is that the association between early cannabis use and educational attainment is not causal, but the result of overlapping risk factors that increase the likelihood of both early cannabis use and disengagement from education. These confounding factors could be of genetic and/or environmental origin.

METHODS

Here we use data from a large community-based sample of adult twins (N=3337) who completed a comprehensive semi-structured telephone interview. We first apply the classical twin-design to determine whether genetic and/or environmental influences underlie the relationship between early-onset cannabis use (prior to age 18) and early school leaving. Next, with a co-twin control design we investigate whether the relationship between the two variables is more likely due to direct causality or overlapping risk factors.

RESULTS

We find a significant phenotypic correlation between early-onset cannabis use and early school leaving (r=0.26), which could be explained by familial influences (of genetic and/or shared environmental origin). The pattern of odds ratios found in the co-twin control design is not consistent with direct causation, but rather suggests that the association is due to shared environmental factors influencing both variables.

CONCLUSION

Our findings suggest that the relationship between early-onset cannabis use and school leaving is due to shared environmental risk factors influencing both the risk of early-onset cannabis use and early school leaving.

Comparação do uso de drogas entre universitários brasileiros, norte-americanos e jovens da população geral brasileira

OBJETIVO: Comparar o uso de drogas entre os universitários e a população geral brasileira, assim como com os universitários norte-americanos, identificando possíveis diferenças de uso pela interferência da cultura. MÉTODOS: Para comparar o uso de drogas na vida entre as populações de interesse, foram utilizados os dados públicos de levantamentos estatísticos brasileiros realizados com universitários e a população geral, assim como levantamento estatístico norte-americano, por meio da comparação de intervalos de confiança (IC 95%). RESULTADOS: O uso de drogas na vida é mais frequente entre os estudantes norte-americanos, que relatam usar mais tabaco, tranquilizantes, maconha, ecstasy, alucinógenos, cocaína, crack e heroína que os universitários brasileiros. Em contrapartida, os universitários brasileiros relatam usar quase duas vezes mais inalantes do que os universitários norte-americanos. Esse padrão se repete ao se analisarem as diferenças intragênero. A isso se soma que os universitários brasileiros parecem envolver-se com mais frequência no uso de bebidas alcoólicas, maconha, tranquilizantes, inalantes, alucinógenos e anfetamínicos que seus pares da população geral brasileira. CONCLUSÕES: Conhecer as particularidades do uso de drogas entre os universitários é de suma importância para a detecção precoce desse consumo. Investimentos nesse segmento e diferenças de sexo devem ser contempladas nas políticas preventivas, assim como na elaboração de estratégias para a redução e o controle desse consumo, como programas de triagem e intervenção breve, uma vez que possuem a melhor relação custo-benefício.

Do early experiences with cannabis vary in cigarette smokers?

INTRODUCTION

We examine whether regular cigarette smokers were more likely to be exposed to and use cannabis at an earlier age, and further, upon initiation, whether their initial experiences with cannabis varied from those reported by never/non-regular cigarette smokers.

METHOD

A sample of 3797 Australian twins and siblings aged 21-46 years was used. Survival analyses examined whether cigarette smokers were at increased likelihood of early opportunity to use cannabis and early onset of cannabis use. Logistic regression examined whether cigarette smokers reported greater enjoyment of their cannabis experience, inhaling on the first try, differing positive and negative initial subjective reactions, smoked cigarettes with cannabis the first time and were more likely to try cannabis again within a week.

RESULTS

Regular cigarette smokers were more likely to report an earlier opportunity to use cannabis and early onset of cannabis use. Regular cigarette smokers were also considerably more likely to have enjoyed their first experience with cannabis and reported higher rates of positive initial reactions. They were more likely to report inhaling on the first try and smoking cigarettes with cannabis. Potentially negative subjective reactions were also elevated in regular cigarette smokers. Importantly, cigarette smokers were at 1.87 increased odds of smoking cannabis within a week of their initial use.

CONCLUSION

These findings indicate that the well-known overlap in cannabis and cigarette smoking behaviors may evolve as early as opportunity to use and extend through the course of the substance use trajectory.

The co-occurring use and misuse of cannabis and tobacco: a review

AIMS

  Cannabis and tobacco use and misuse frequently co-occur. This review examines the epidemiological evidence supporting the life-time co-occurrence of cannabis and tobacco use and outlines the mechanisms that link these drugs to each other. Mechanisms include (i) shared genetic factors; (ii) shared environmental influences, including (iii) route of administration (via smoking), (iv) co-administration and (v) models of co-use. We also discuss respiratory harms associated with co-use of cannabis and tobacco, overlapping withdrawal syndromes and outline treatment implications for co-occurring use.

METHODS

  Selective review of published studies.

RESULTS

  Both cannabis and tobacco use and misuse are influenced by genetic factors, and a proportion of these genetic factors influence both cannabis and tobacco use and misuse. Environmental factors such as availability play an important role, with economic models suggesting a complementary relationship where increases in price of one drug decrease the use of the other. Route of administration and smoking cues may contribute to their sustained use. Similar withdrawal syndromes, with many symptoms in common, may have important treatment implications. Emerging evidence suggests that dual abstinence may predict better cessation outcomes, yet empirically researched treatments tailored for co-occurring use are lacking.

CONCLUSIONS

  There is accumulating evidence that some mechanisms linking cannabis and tobacco use are distinct from those contributing to co-occurring use of drugs in general. There is an urgent need for research to identify the underlying mechanisms and harness their potential etiological implications to tailor treatment options for this serious public health challenge.

Autosomal linkage scan for loci predisposing to comorbid dependence on multiple substances

Multiple substance dependence (MSD) trait comorbidity is common, and MSD patients are often severely affected clinically. While shared genetic risks have been documented, so far there has been no published report using the linkage scan approach to survey risk loci for MSD as a phenotype. A total of 1,758 individuals in 739 families [384 African American (AA) and 355 European American (EA) families] ascertained via affected sib-pairs with cocaine or opioid or alcohol dependence were genotyped using an array-based linkage panel of single-nucleotide polymorphism markers. Fuzzy clustering analysis was conducted on individuals with alcohol, cannabis, cocaine, opioid, and nicotine dependence for AAs and EAs separately, and linkage scans were conducted for the output membership coefficients using Merlin-regression. In EAs, we observed an autosome-wide significant linkage signal on chromosome 4 (peak lod = 3.31 at 68.3 cM; empirical autosome-wide P = 0.038), and a suggestive linkage signal on chromosome 21 (peak lod = 2.37 at 19.4 cM). In AAs, four suggestive linkage peaks were observed: two peaks on chromosome 10 (lod = 2.66 at 96.7 cM and lod = 3.02 at 147.6 cM] and the other two on chromosomes 3 (lod = 2.81 at 145.5 cM) and 9 (lod = 1.93 at 146.8 cM). Three particularly promising candidate genes, GABRA4, GABRB1, and CLOCK, are located within or very close to the autosome-wide significant linkage region for EAs on chromosome 4. This is the first linkage evidence supporting existence of genetic loci influencing risk for several comorbid disorders simultaneously in two major US populations.

Genetic and environmental influences underlying externalizing behaviors, cigarette smoking and illicit drug use across adolescence

We investigated genetic and environmental influences common to adolescent externalizing behavior (at age 12), smoking (at age 14) and initiation of drug use (at age 17) using the FinnTwin12 cohort data. Multivariate Cholesky models were fit to data from 737 monozygotic and 722 dizygotic twin pairs. Heritability of externalizing behavior was 56%, that of smoking initiation/amount 20/32%, and initiation of drug use 27%. In the best-fitting model common environmental influences explained most of the covariance between externalizing behavior and smoking initiation (69%) and amount (77%). Covariance between smoking initiation/amount and drug use was due to additive genetic (42/22%) and common environmental (58/78%) influences. Half of the covariance between externalizing behavior and drug use was due to shared genetic and half due to the environments shared by co-twins. Using a longitudinal, prospective design, our results indicate that early observed externalizing behavior provides significant underlying genetic and environmental influences common to later substance use, here manifested as initiation of drug use in late adolescence.

Patterns of use, sequence of onsets and correlates of tobacco and cannabis

BACKGROUND

While most individuals initiate their use of tobacco prior to onset of cannabis use, recent reports have identified a smaller subset of youth who report onset of cannabis use prior to tobacco use. In this study, we characterize patterns of cannabis and tobacco use (tobacco but not cannabis, cannabis but not tobacco or both) and compare the factors associated with onset of tobacco before cannabis and cannabis before tobacco.

METHODS

Data on 1812 offspring aged 12-32 years, drawn from two related offspring of Vietnam Era twin studies, were used. Individuals were divided into tobacco but not cannabis (T), cannabis but not tobacco (C) and users of both substances (CT). Those who used both could be further classified by the timing of onset of tobacco and cannabis use. Multinomial logistic regression was used to characterize the groups using socio-demographic and psychiatric covariates. Furthermore, data on parental smoking and drug use was used to identify whether certain groups represented greater genetic or environmental vulnerability.

RESULTS

22% (N=398) reported T, 3% (N=55) reported C and 44% reported CT (N=801). Of the 801 CT individuals, 72.8% (N=583), 9.9% (N=77) and 17.3% (N=139) reported onset of tobacco before cannabis, cannabis before tobacco and onsets at the same age. C users were as likely as CT users to report peer drug use and psychopathology, such as conduct problems while CT was associated with increased tobacco use relative to T. Onset of tobacco prior to cannabis, when compared onset of cannabis before tobacco or reporting initiation at the same age was associated with greater cigarettes smoked per day, however no distinct factors distinguished the group with onset of cannabis before tobacco from those with initiation at the same age.

CONCLUSION

A small subset of individuals report cannabis without tobacco use. Of those who use both cannabis and tobacco, a small group report cannabis use prior to tobacco use. Follow-up analyses that chart the trajectories of these individuals will be required to delineate their course of substance involvement.

Age moderates non-genetic influences on the initiation of cannabis use: a twin-sibling study in Dutch adolescents and young adults

AIMS

To examine the heritability of cannabis initiation, the influence of a possible twin-specific environment and the influence of age on the effects of genes and environment in Dutch adolescents and young adults.

DESIGN

Genetic structural equation modelling was used to partition the variance in the liability to cannabis initiation into genetic and environmental components.

SETTING

All participants were registered with the Netherlands Twin Register.

PARTICIPANTS

A total of 6,208 twins (age 13-20) and 1,545 siblings (age 11-25) from 3,503 families participated in this study.

MEASUREMENTS

Self-reported cannabis use was assessed prospectively with the Dutch Health Behavior Questionnaire.

FINDINGS

At the median age of the sample (16.5), genetic factors explained 40% of the individual differences in liability to cannabis initiation. Twins resembled each other more than non-twin siblings, which could not be attributed to the age difference between non-twin siblings. Environmental influences increased with age. This increase applied to environmental factors shared by twins (47% of the variance), environmental factors shared by twins and siblings (24%) and environmental factors unique to an individual (13%).

CONCLUSION

The heritability of the liability for cannabis initiation is higher in adolescents than in young adults due to a larger contribution of environmental factors in young adults. This is due mainly to environmental factors only shared by twins and those shared by all offspring growing up in the same family, but the contribution of environmental factors specific to individuals is also larger in young adults.

Can the gateway hypothesis, the common liability model and/or, the route of administration model predict initiation of cannabis use during adolescence? A survival analysis--the TRAILS study

PURPOSE

There is substantial research linking tobacco and alcohol use to subsequent cannabis use, yet the specificity of this relationship is still under debate. The aim of this study was to examine which substance use model--the gateway hypothesis, the common liability (CL) model and/or the route of administration model--best explains the relationship between early onset of tobacco and alcohol use and subsequent cannabis use initiation.

METHODS

We used data from 2,113 (51% female) Dutch adolescents who participated in three consecutive assessment waves (mean age: 11.09, 13.56, and 16.27 years, respectively) of the TRacking Adolescents' Individual Lives Survey study. (Pre)adolescent cannabis, tobacco and alcohol use was assessed using the Youth Self-Report and a TRacking Adolescents' Individual Lives Survey developed questionnaire.

RESULTS

We found that, during adolescence, early onset of tobacco use does not pose a significantly higher risk of initiating cannabis use than early onset alcohol use. Therefore, we can rule out the route of administration model. Moreover, we found that adolescents who reported early onset comorbid use of both tobacco and alcohol have a higher likelihood to initiate cannabis use than adolescents who have tried either tobacco or alcohol. The gateway hypothesis is not broad enough to explain this finding. Therefore, the CL model best predicts our findings.

CONCLUSION

Future research on adolescent cannabis initiation should focus on testing the robustness of the CL model. Furthermore, identifying adolescents who use both tobacco and alcohol, before the age of 13, may help to curtail the onset of cannabis use.

Genetically informative research on adolescent substance use: methods, findings, and challenges

OBJECTIVE

To provide an overview of the genetic epidemiology of substance use and misuse in adolescents.

METHOD

A selective review of genetically informative research strategies, their limitations, and key findings examining issues related to the heritability of substance use and substance use disorders in children and adolescents is presented.

RESULTS

Adoption, twin, and extended-family designs have established there is a strong heritable component to liability to nicotine, alcohol, and illicit drug dependence in adults. However, shared environmental influences are relatively stronger in youth samples and at earlier stages of substance involvement (e.g., use). There is considerable overlap in the genetic influences associated with the abuse/dependence across drug classes, and shared genetic influences contribute to the commonly observed associations between substance-use disorders and externalizing and, to a lesser extent, internalizing psychopathology. Rapid technologic advances have made the identification of specific gene variants that influence risks for substance-use disorders feasible, and linkage and association (including genomewide association studies) have identified promising candidate genes implicated in the development of substance-use disorders.

CONCLUSIONS

Studies using genetically informative research designs, including those that examine aggregate genetic factors and those examining specific gene variants, individually and in interaction with environmental influences, offer promising avenues not only for delineating genetic effects on substance-use disorders but also for understanding the unfolding of risk across development and the interaction between environmental and genetic factors in the etiology of these disorders.