Human behavioral pharmacology of stimulant drugs: An update and narrative review

Stimulant use disorders present an enduring public health concern. Chronic stimulant use is associated with a range of health problems, with notable increases in stimulant overdose that disproportionately affect marginalized populations. With these persistent problems, it is important to understand the behavioral and pharmacological factors that contribute to stimulant use in humans. The purpose of this chapter is to provide an update and narrative review on recent human laboratory research that has evaluated the behavioral pharmacology of stimulant drugs. We focus on two prototypic stimulants: cocaine as a prototype monoamine reuptake inhibitor and d-amphetamine as a prototype monoamine releaser. As such, placebo controlled human laboratory studies that involved administration of doses of cocaine or d-amphetamine and were published in peer reviewed journals within the last 10 years (i.e., since 2011) are reviewed. Primary outcomes from these studies are subjective effects, reinforcing effects, cognitive/behavioral effects, and discriminative stimulus effects. Both cocaine and d-amphetamine produce classical stimulant-like behavioral effects (e.g., increase positive subjective effects, function as reinforcers), but there are notable gaps in the literature including understanding sex differences in response to stimulant drugs, cognitive-behavioral effects of stimulants, and influence of use history (e.g., relatively drug naïve vs drug experienced) on stimulant effects.

Personality to Prescription Drug Misuse in Adolescents: Testing Affect Regulation, Psychological Dysregulation, and Deviance Proneness Pathways

Background: Fifteen to 25-year-olds are the age group most likely to misuse prescription drugs. Few studies have tested theory-driven models of adolescent risk for prescription drug misuse. Moreover, rarely are distinct pathways to different forms of prescription drug misuse considered. Methods: We tested mediational paths from personality to mental health symptoms to prescription drug misuse, informed by etiological models of addiction. We specified pathways from particular personality traits to unique forms of prescription drug misuse via specific mental health symptoms. We used semi-longitudinal data collected across two waves of the Co-Venture Trial. Our sample included students from 31 Canadian high schools tested in Grade 9 (n = 3,024) and again in Grade 10 (n = 2,869; 95% retention). Personality (hopelessness, anxiety sensitivity, impulsivity, sensation seeking) was assessed in Grade 9. Mental health symptoms (depression, anxiety, ADHD, conduct disorder) and prescription drug misuse (opioids, sedatives/tranquilizers, stimulants) were assessed at both time points. Results: Consistent with the negative affect regulation model, hopelessness was specifically associated with opioid misuse via depressive symptoms, and anxiety sensitivity was specifically associated with sedative/tranquilizer misuse via anxiety symptoms. Consistent with positive affect regulation, sensation seeking was directly associated with stimulant misuse. Consistent with the psychological dysregulation model, impulsivity was associated with stimulant misuse via ADHD symptoms. And consistent with the deviance proneness model, impulsivity was also associated with unconstrained (i.e., all three forms of) prescription drug misuse via conduct disorder symptoms. Conclusions: Screening for adolescents high in hopelessness, anxiety sensitivity, sensation seeking, or impulsivity and providing them with personality-matched cognitive-behavioral interventions may be helpful in preventing or mitigating prescription drug misuse. Our results point to the specific mental health symptoms that are important to target in each of these personality-matched interventions.

Subjective responses predict d-amphetamine choice in healthy volunteers

BACKGROUND

It is commonly believed that drugs, including stimulants, are used recreationally because of their ability to induce pleasurable subjective effects. However, recreational drug use sometimes occurs in the absence of positive subjective effects, suggesting that other factors contribute. Here, we examine the extent to which the direct subjective effects of amphetamine, a commonly misused stimulant, predict subsequent choice of the drug vs placebo.

METHODS

Healthy adults (N = 112) participated in a five-session amphetamine choice study. On the first four sessions, participants sampled either 20 mg d-amphetamine or placebo in color-coded capsules two times each. On the fifth session, they chose which color (d-amphetamine or placebo) they preferred. We examined the choice of drug vs placebo in relation to demographic characteristics, baseline mood states, personality and subjective and cardiovascular responses to acute administration of the drug.

RESULTS

Eighty-one participants chose amphetamine (Choosers) while 31 chose placebo (Non-choosers). Overall, amphetamine produced typical stimulant-like effects on subjective questionnaires, and it elevated heart rate and blood pressure vs placebo. Choosers reported greater positive mood, elation and stimulant-like effects following amphetamine compared to Non-choosers. The Choosers also exhibited a greater increase in systolic blood pressure, but not heart rate. The groups did not differ on demographic characteristics, mood states before drug administration or personality.

CONCLUSIONS

These findings support the idea that pleasurable subjective responses to amphetamine, including positive mood, elation, and stimulant-like effects influence behavioral choice of the drug.

Comorbidity, family history and personality traits in pathological gamblers compared with healthy controls

Background

While DSM-5 classified pathological gambling as an addictive disorder, there is debate as to whether ICD-11 should follow suit. The debate hinges on scientific evidence such as neurobiological findings, family history of psychiatric disorders, psychiatric comorbidity, and personality variables.

Methods

In the “Baden-Württemberg Study of Pathological Gambling”, we compared a group of 515 male pathological gamblers receiving treatment with 269 matched healthy controls. We studied differences in sociodemographic characteristics, gambling-related variables, psychiatric comorbidity (lifetime), family history of psychiatric conditions, as well as personality traits such as impulsivity (Barratt Impulsiveness Scale), sensation seeking (Zuckerman's Sensation Seeking Scale) and the NEO-FFI big five. Personality traits were validated in an age- and ethnicity-matched subsample of “pure” gamblers without any psychiatric comorbidity (including nicotine dependence). Data were analyzed using two-sample t-tests, Chi2 analyses, Fisher's exact test and Pearson correlation analysis, as appropriate. Bonferroni correction was applied to correct for multiple comparisons.

Results

Only 1% of the gamblers had been diagnosed with an impulse control disorder other than gambling (ICD-10). Notably, 88% of the gamblers in our sample had a comorbid diagnosis of substance dependence. The highest axis I comorbidity rate was for nicotine dependence (80%), followed by alcohol dependence (28%). Early age of first gambling experience was correlated with gambling severity. Compared to first-degree relatives of controls, first-degree relatives of pathological gamblers were more likely to suffer from alcohol dependence (27.0% vs. 7.4%), pathological gambling (8.3% vs. 0.7%) and suicide attempts (2.7% vs. 0.4%). Significant group differences were observed for the NEO-FFI factors neuroticism, agreeableness and conscientiousness. Gamblers were also more impulsive than controls, but did not differ from controls in terms of sensation seeking.

Conclusions

Our findings support classifying pathological gambling as a behavioural addiction in the ICD-11. This decision will have a significant impact on the approaches available for prevention (e.g. age limits) and treatment.

Subjective responses to amphetamine in young adults with previous mood elevation experiences

RATIONALE

One risk factor for alcohol and substance misuse is hypomanic experiences, or periods of mood elevation. Young people who report hypomanic states are more likely to develop bipolar disorder (BP), and BP and other mood disorders increase the risk of addiction. We recently reported that young adults with a history of mood elevation experience less subjective effects from a low dose of alcohol, which may be predictive of future alcohol use. The finding with alcohol raised the question of whether this dampened response to a drug also applies to other drugs, such as amphetamine.

OBJECTIVE

This study assessed responses of d-amphetamine in healthy young adults with varying experiences of mood elevation, as measured by the Mood Disorders Questionnaire (MDQ).

METHODS

Healthy 18-19-year-olds (N = 30) with a range of MDQ scores participated in three 4-h laboratory sessions in which they received placebo, 10 mg, or 20 mg d-amphetamine. They completed mood questionnaires and cardiovascular measures.

RESULTS

Individuals with higher MDQ scores reported less stimulation and euphoria after 10 mg, but not 20 mg, d-amphetamine, than individuals with lower scores. MDQ scores were not related to cardiovascular responses to the drug.

CONCLUSIONS

A history of mood elevation experiences or hypomania states is related to dampened response to a low dose of a psychostimulant drug, extending previous findings with dampened response to alcohol. This phenotype for mood disorders of dampened responses to drugs may contribute to risk for subsequent drug use or misuse.

Beyond Sensation Seeking: A Conceptual Framework for Individual Differences in Psychostimulant Drug Effects in Healthy Humans

Psychostimulant addiction is an important, relapsing condition for which there is no effective pharmacological treatment. Countering this problem requires an understanding of the specific risk factors that predispose individuals to initial misuse of these drugs. Healthy individuals display marked individual differences in emotional, behavioral and brain responses to low and moderate doses of stimulant drugs. These between-person differences have been most often studied using personality measures of sensation seeking. However, a growing body of work in healthy adults indicates potentially unique sources of variance in these responses that are related to four dissociable personality domains: extraversion, fearlessness, impulsivity and absorption. These four domains are empirically dissociable and can serve as endophenotypic markers of dopamine, norepinephrine and serotonin function in healthy individuals. The relationship between normal variation in these traits and the pharmacological effects of these drugs is here proposed as a framework for better understanding the specific sources of between-person variation in stimulant drug effects on mood, behavior and brain responses in healthy humans.