Preference for high- versus low-potency marijuana

Characteristics that influence purchase choice for cannabis products: a systematic review

Introduction

When non-medical cannabis use became legal, government regulators implemented policies to encourage safer consumption through access to a regulated market. While this market is growing, sales still occur through unregulated channels. This systematic review identifies factors influencing cannabis purchasing to help policymakers understand why consumers still purchase illicit market cannabis (registered with PROSPERO CRD42020176079).

Methods

A comprehensive search strategy included databases in health, business, and social science fields (inception to June 2020). Studies were eligible for inclusion if they were conducted with persons who purchase cannabis and examine at least one attribute that would influence purchase choice and were published in the English language. Studies could be of any methodological design. Two independent reviewers completed two levels of screening, and all extraction was verified by a second reviewer. A qualitative synthesis of the findings was completed. The quality of the included studies was assessed using the Mixed Methods Appraisal Tool.

Results

Of the 4839 citations screened, 96 were eligible for full-text review and 35 were included in the final synthesis. Aspects of price were the most common factors (27 studies). Twenty studies measured price elasticity; most studies found that demand was price inelastic. Many other attributes were identified (e.g., product quality, route of administration, product recommendations, packaging), but none were explored in depth. Eleven studies addressed aspects of product quality including demand elasticity based on quality, potency, and aroma. Studies also explored consumer-perceived “quality” but provided no definition; differences in quality appeared to impact consumer choice. Smoking cannabis appeared to be the preferred route of administration but was only examined in three studies. There was insufficient data to understand in the impact of other attributes on choice. There appeared to be preference heterogeneity for different attributes based on the consumer’s experience, reason for use, and gender.

Conclusion

While price influences choices, demand is relatively inelastic. This suggests that consumers may be seeking lowest-cost, unregulated cannabis to avoid reducing consumption. Beyond price, there is a significant gap in our understanding of consumer choices. Perceived quality does appear to impact choice; however, more research is needed due to the lack of a recognized definition for cannabis quality.

Supplementary Information

The online version contains supplementary material available at 10.1186/s42238-022-00117-0.

Associations between self-reported cannabis use frequency, potency, and cannabis/health metrics

BACKGROUND

Research shows that cannabis use frequency is associated with cannabis dependence and health metrics. However, much less is known about how self-reported cannabis potency (THC and CBD) may be associated with the same metrics, and whether any associations exist after accounting for frequency of cannabis use. Moreover, even less is known about how these relations may differ across cannabis product forms. This exploratory study examined 1) associations between cannabis frequency, potency, and cannabis/health metrics, and 2) whether associations between potency and cannabis/health metrics remained after controlling for frequency of use.

METHODS

Using a sample of adult recreational cannabis users in Colorado (N = 300), we tested the relationship between self-reported cannabis use metrics of frequency and potency of flower, edible, and concentrate products with separate measures of problematic cannabis use (i.e., dependence, withdrawal, craving), depression, anxiety, and general perceived health.

RESULTS

Greater frequency of flower and concentrate (but not edible) use were associated with greater problematic cannabis use, and greater concentrate use frequency was also associated with more mental health problems. Partial correlations controlling for average frequency of use across all product forms and CBD potency per product showed that one significant association between THC potency and cannabis/health metrics remained (i.e., higher THC concentrate potency with better health), and one emerged (i.e., higher THC concentrate potency with lower cannabis withdrawal).

CONCLUSIONS

Frequency of use is reliably associated with problematic cannabis use for flower and concentrates, but it did not account for all observed associations in this study. Differences in patterns of associations between frequency and potency and cannabis/health metrics across cannabis forms suggest a need for better understanding user reports of THC and CBD potency, individual differences among users, and improved measurement.

A within-person comparison of the subjective effects of higher vs. lower-potency cannabis

BACKGROUND

Cannabis concentrates have much higher concentrations of THC than marijuana (flower) and are quickly gaining popularity in the United States. One hypothesis is that use of higher-THC cannabis (concentrates) might result in greater intoxication and more severe acute negative effects than lower-THC cannabis (marijuana), but few studies have compared the subjective effects of concentrates and marijuana.

METHODS

Current (past-year) cannabis users were recruited online to complete a survey about their cannabis use. Cannabis users who reported using both marijuana and concentrates (n = 574) answered questions about the subjective effects of marijuana and, subsequently, the subjective effects of concentrates. Subjective effects were obtained for the following domains: affect, cognitive function, psychotic-like experiences, physiological effects, and reduced consciousness.

RESULTS

Participants reported using marijuana between 5-6 times per week and concentrates slightly more than once per month. Within-person comparisons of the subjective effects of marijuana and concentrates showed that marijuana was rated as producing greater overall positive effects (Marijuana: M = 5.6, Concentrates: M = 4.5; Cohen's d = 0.75, paired t(561) = 14.67, p < .001), including greater positive affect and enhanced cognitive function. Negative effects of both marijuana and concentrates were minimal. Marijuana was selected over concentrates as the 'preferred type' of cannabis by 77.5 % of participants.

CONCLUSIONS

The main difference in the subjective effects of marijuana and concentrates is in terms of their positive effects, with marijuana producing greater positive effects than concentrates. Negative effects of marijuana and concentrates were small, suggesting that extreme negative effects are unlikely for regular cannabis users.

Cannabis Concentrate Use in Adolescents

BACKGROUND

Cannabis concentrates, which are cannabis plant extracts that contain high concentrations of Δ-9-tetrahydrocannbinol (THC), have become increasingly popular among adults in the United States. However, no studies have reported on the prevalence or correlates of cannabis concentrate use in adolescents, who, as a group, are thought to be particularly vulnerable to the harms of THC.

METHODS

Participants are a racially and ethnically diverse group of 47 142 8th-, 10th-, and 12th-grade students recruited from 245 schools across Arizona in 2018. Participants reported on their lifetime and past-month marijuana and cannabis concentrate use, other substance use, and risk and protective factors for substance use problems spanning multiple life domains (ie, individual, peer, family, school, and community).

RESULTS

Thirty-three percent of all 8th-, 10th-, and 12th-graders reported lifetime cannabis use, and 24% reported lifetime concentrate use. Seventy-two percent of all lifetime cannabis users had used concentrates. Relative to adolescent cannabis users who had not used concentrates, adolescent concentrate users were more likely to use other substances and to experience more risk factors, and fewer protective factors, for substance use problems across numerous life domains.

CONCLUSIONS

Most adolescent cannabis users have used concentrates. Based on their risk and protective factor profile, adolescent concentrate users are at higher risk for substance use problems than adolescent cannabis users who do not use concentrates. Findings raise concerns about high-risk adolescents' exposure to high-THC cannabis.

Associations between butane hash oil use and cannabis-related problems

BACKGROUND

High-potency cannabis concentrates are increasingly popular in the United States, and there is concern that use of high-potency cannabis might increase risk for cannabis-related problems. However, little is known about the potential negative consequences of concentrate use. This study reports on associations between past-year use of a high-potency cannabis concentrate, known as butane hash oil (BHO), and cannabis-related problems.

METHODS

A sample of 821 college students were recruited to complete a survey about their health and behavior. Participants who had used cannabis in the past year (33%, n=273) completed questions about their cannabis use, including their use of BHO and cannabis-related problems in eight domains: physical dependence, impaired control, academic-occupational problems, social-interpersonal problems, self-care problems, self-perception, risk behavior, and blackouts.

RESULTS

Approximately 44% (n=121) of past-year cannabis users had used BHO in the past year. More frequent BHO use was associated with higher levels of physical dependence (RR=1.8, p<0.001), impaired control (RR=1.3, p<0.001), cannabis-related academic/occupational problems (RR=1.5, p=0.004), poor self-care (RR=1.3, p=0.002), and cannabis-related risk behavior (RR=1.2, p=0.001). After accounting for sociodemographic factors, age of onset of cannabis use, sensation seeking, overall frequency of cannabis use, and frequency of other substance use, BHO use was still associated with higher levels of physical dependence (RR=1.2, p=0.014).

CONCLUSIONS

BHO use is associated with greater physiological dependence on cannabis, even after accounting for potential confounders. Longitudinal research is needed to determine if cannabis users with higher levels of physiological dependence seek out BHO and/or if BHO use increases risk for physiological dependence.

[Consumption of cannabis in adolescents]

Over the past 10 years, the consumption of cannabis among adolescents has dramatically increased. Today, adolescent cannabis use is a major public health problem. Two forms of cannabis are commonly smoked: herb (marijuana) and resin. These forms have a high concentration of tetrahydrocannabinol, the active molecule of cannabis. Recent research has helped understand how the cannabinoid system works. This system combines specific receptors and specific molecules: the endocannabinoids. The effects of cannabis use are now well documented. Some adolescents report subjective positive effects. They use it not only on a recreational basis, but also to deal with their emotions. Over the long term, cannabis increases the risk of depression and schizophrenia for those adolescents who are at risk. Use, misuse, and dependence are frequently associated with heavy psychopathologic problems such as vulnerability and depression. Many cannabis dependence psychotherapies have shown their efficacy and efficiency. Motivational interviews, cognitive behavioral therapy, multidimensional family therapy (MDFT), and residential treatment have proved highly effective. MDFT seems very effective, especially in cases of heavy use.

Acute effects of THC on time perception in frequent and infrequent cannabis users

RATIONALE

Cannabinoids have been shown to alter time perception, but existing literature has several limitations. Few studies have included both time estimation and production tasks, few control for subvocal counting, most had small sample sizes, some did not record subjects' cannabis use, many tested only one dose, and used either oral or inhaled administration of Δ⁹-tetrahydrocannabinol (THC), leading to variable pharmacokinetics, and some used whole-plant cannabis containing cannabinoids other than THC. Our study attempted to address these limitations.

OBJECTIVES

This study aims to characterize the acute effects of THC and frequent cannabis use on seconds-range time perception. THC was hypothesized to produce transient, dose-related time overestimation and underproduction. Frequent cannabis smokers were hypothesized to show blunted responses to these alterations.

METHODS

IV THC was administered at doses from 0.015 to 0.05 mg/kg to 44 subjects who participated in several double-blind, randomized, counterbalanced, crossover, placebo-controlled studies. Visual time estimation and production tasks in the seconds range were presented to subjects three times on each test day.

RESULTS

All doses induced time overestimation and underproduction. Chronic cannabis use had no effect on baseline time perception. While infrequent/nonsmokers showed temporal overestimation at medium and high doses and temporal underproduction at all doses, frequent cannabis users showed no differences. THC effects on time perception were not dose related.

CONCLUSIONS

A psychoactive dose of THC increases internal clock speed as indicated by time overestimation and underproduction. This effect is not dose related and is blunted in chronic cannabis smokers who did not otherwise have altered baseline time perception.

Smoked cannabis for chronic neuropathic pain: a randomized controlled trial

BACKGROUND

Chronic neuropathic pain affects 1%-2% of the adult population and is often refractory to standard pharmacologic treatment. Patients with chronic pain have reported using smoked cannabis to relieve pain, improve sleep and improve mood.

METHODS

Adults with post-traumatic or postsurgical neuropathic pain were randomly assigned to receive cannabis at four potencies (0%, 2.5%, 6% and 9.4% tetrahydrocannabinol) over four 14-day periods in a crossover trial. Participants inhaled a single 25-mg dose through a pipe three times daily for the first five days in each cycle, followed by a nine-day washout period. Daily average pain intensity was measured using an 11-point numeric rating scale. We recorded effects on mood, sleep and quality of life, as well as adverse events.

RESULTS

We recruited 23 participants (mean age 45.4 [standard deviation 12.3] years, 12 women [52%]), of whom 21 completed the trial. The average daily pain intensity, measured on the 11-point numeric rating scale, was lower on the prespecified primary contrast of 9.4% v. 0% tetrahydrocannabinol (5.4 v. 6.1, respectively; difference = 0.7, 95% confidence interval [CI] 0.02-1.4). Preparations with intermediate potency yielded intermediate but nonsignificant degrees of relief. Participants receiving 9.4% tetrahydrocannabinol reported improved ability to fall asleep (easier, p = 0.001; faster, p < 0.001; more drowsy, p = 0.003) and improved quality of sleep (less wakefulness, p = 0.01) relative to 0% tetrahydrocannabinol. We found no differences in mood or quality of life. The most common drug-related adverse events during the period when participants received 9.4% tetrahydrocannabinol were headache, dry eyes, burning sensation in areas of neuropathic pain, dizziness, numbness and cough.

CONCLUSION

A single inhalation of 25 mg of 9.4% tetrahydrocannabinol herbal cannabis three times daily for five days reduced the intensity of pain, improved sleep and was well tolerated. Further long-term safety and efficacy studies are indicated. (International Standard Randomised Controlled Trial Register no. ISRCTN68314063).

Increased cannabinoids concentrations found in specimens from fatal aviation accidents between 1997 and 2006

The National Institute on Drug Abuse (NIDA) and the Office of National Drug Control Policy (ONDCP) reported a 1.5-fold increase in the delta-9-tetrahydrocannabinol (THC) content of street cannabis seizures from 1997 to 2001 versus 2002 to 2006. This study was conducted to compare the changes, over those years, in blood and urine cannabinoid concentrations with the potency of THC reported in the cannabis plant. Cannabinoids were screened using radioimmunoassay (RIA) for blood and fluorescence polarization immunoassay (FPIA) for urine and confirmed using GC/MS. A total of 95 individuals were found to be using cannabis from a total number of 2769 (3.4%) individuals tested over the period 1997 through 2006. Other impairing drugs were found in 38% of the cannabinoids-positive individuals. The mean concentration of THC in blood for 1997-2001 was 2.7 ng/mL; for 2002-2006, it was 7.2 ng/mL, a 2.7-fold increase in the mean THC concentration of specimens from aviation fatalities, compared to a 1.5-fold increase in cannabis potency reported by the NIDA and ONDCP. The mean age for cannabis users was 40 years (range 18-72) for aviation fatalities. For all blood and urine specimens testing negative for cannabinoids from aviation fatalities, the mean age of the individuals was 50 years (range 14-92). More than half of the fatalities tested were 50 years or older, whereas, 80% of the positive cannabis users were under 50. As indicated by these findings, members of the transportation industry, government regulators, and the general public should be made aware of the increased potential for impairment from the use of high-potency cannabis currently available and being used.

Self-administration of cocaine, cannabis and heroin in the human laboratory: benefits and pitfalls

The objective of this review is to describe self-administration procedures for modeling addiction to cocaine, cannabis and heroin in the human laboratory, the benefits and pitfalls of the approach, and the methodological issues unique to each drug. In addition, the predictive validity of the model for testing treatment medications will be addressed. The results show that all three drugs of abuse are reliably and robustly self-administered by non-treatment-seeking research volunteers. In terms of pharmacotherapies, cocaine use is extraordinarily difficult to disrupt either in the laboratory or in the clinic. A range of medications has been shown to significantly decrease cocaine's subjective effects and craving without decreasing either cocaine self-administration or cocaine abuse by patients. These negative data combined with recent positive findings with modafinil suggest that self-administration procedures are an important intermediary step between pre-clinical and clinical studies. In terms of cannabis, a recent study suggests that medications that improve sleep and mood during cannabis withdrawal decrease the resumption of marijuana self-administration in abstinent volunteers. Clinical data on patients seeking treatment for their marijuana use are needed to validate these laboratory findings. Finally, in contrast to cannabis or cocaine dependence, there are three efficacious Food and Drug Administration-approved medications to treat opioid dependence, all of which decrease both heroin self-administration and subjective effects in the human laboratory. In summary, self-administration procedures provide meaningful behavioral data in a small number of individuals. These studies contribute to our understanding of the variables maintaining cocaine, marijuana and heroin intake, and are important in guiding the development of more effective drug treatment programs.

Differential responses to cannabis potency: A typology of users based on self-reported consumption behaviour

AIMS

To determine whether a classification of cannabis users into different types can help to clarify the relationship between cannabis potency and consumption behaviour, harmful physical effects and psychological dependency.

METHODS

A field sample of 388 respondents was recruited who had smoked cannabis at least once in the past month. They were contacted and interviewed in 28 cannabis coffee shops located in five Dutch cities. Data were collected with an assisted self-completion questionnaire. Cluster analysis was performed using the k-means method.

FINDINGS

Various ways were observed in which cannabis users in natural settings adjusted their intake to the potency of the drug. Cluster analysis identified three broad types of cannabis users. The strongest high type was the youngest, consumed the highest monthly dose, inhaled higher-potency cannabis more deeply, and scored highest on psychological cannabis dependency. The consistent high type preferred milder cannabis, consumed the lowest monthly dose, and compensated for stronger cannabis by inhaling less deeply and smoking less. The steady quantity type was the oldest, usually smoked alone, consumed an intermediate monthly dose, and did not tend to adjust the depth of inhalation to the potency of the cannabis. The results suggest that this typology might also reflect three successive stages in the careers of continuing cannabis users.

CONCLUSIONS

Laboratory studies to assess the effects of higher THC concentrations on external and internal exposure to cannabis should allow for the possibility that the types of users studied can affect the results.

Strain and schedule-dependent differences in the acquisition, maintenance and extinction of intravenous cannabinoid self-administration in rats

Cannabinoids have been reported to sustain self-administration in laboratory animals; however, genetic differences and environmental factors critical in the initiation and retention of such behaviour are yet to be defined. This study investigated the acquisition, maintenance and extinction of self-administration of the cannabinoid CB1 receptor agonist WIN 55,212-2 (6.25-25 microg/kg/inf) in Long Evans, Lister Hooded and Sprague-Dawley rats under a continuous schedule of reinforcement and two different response-like operanda, nose-poking and lever-pressing. Results showed that Long Evans and Lister Hooded, but not Sprague Dawley, rats acquired and retained stable cannabinoid self-administration behaviour under both modus operandi, as defined by significant differences between responding in the active versus the inactive hole/lever. In rats developing firm self-administration, substitution of saline for WIN 55,212-2 extinguished the responding, supporting the notion that cannabinoids may serve as a positive reinforcer in laboratory animals. Nevertheless, significant differences among strains and responding modalities were observed in the percentage of acquisition, amount of drug intake during maintenance and timing of extinction. In addition, no significant strain differences were found in motor response to WIN 55,212-2 (0.3 and 3.0 mg/kg), thus excluding that strain differences observed during cannabinoid self-administration could be related to different cannabinoid-induced locomotor effects.

High-potency marijuana impairs executive function and inhibitory motor control

Human performance studies have usually relied on low-potency marijuana (4% THC) for determining THC-induced impairment. The present study was designed to assess the effects of high-potency marijuana (13% THC) on human performance. In all, 20 recreational users of marijuana participated in a double-blind, placebo controlled, three way cross-over study. The treatments consisted of single doses of 0, 250, and 500 microg/kg THC. Performance tests were conducted at regular intervals between 15 min and 6 h postsmoking and included measures of motor control (Critical tracking task), executive function (Tower of London) motor impulsivity (Stop signal task), and risk taking (Iowa gambling task). THC significantly impaired performance in the Critical tracking task and decreased the number of correct decisions in the Tower of London task. In addition, THC significantly increased stop reaction time and the proportions of commission and omission errors in the Stop signal task. THC-induced impairments lasted up to 6 h postsmoking as indicated by the absence of a THC x Time after smoking interaction. Effect sizes for performance impairments produced by THC 250 microg/kg were relatively low but generally increased by a factor of two in case of THC 500 microg/kg. These data suggest that high potency marijuana consistently impairs executive function and motor control. Use of higher doses of THC in controlled studies may offer a reliable indication of THC induced impairment as compared to lower doses of THC that have traditionally been used in performance studies.

Effects of nabilone, a synthetic cannabinoid, on postoperative pain

PURPOSE

Cannabinoids have been shown to have analgesic properties in animal studies, but a potential role for these drugs in acute pain management has not been established. It was hypothesized that nabilone, an oral cannabinoid synthetic tetrahydrocannabinol analogue, decreases morphine consumption, pain scores, nausea and vomiting following major surgery.

METHODS

A double-blind, randomized, placebo-controlled, parallel-group pilot trial compared the effects of two different doses, 1 mg (n = 11) and 2 mg (n = 9) of nabilone, ketoprofen 50 mg (n = 11) or placebo (n = 10), given at eight-hour intervals for 24 hr. Outcomes included morphine consumption, pain scores and emesis after major surgery. Secondary outcomes included patient tolerability of the study medication.

RESULTS

Forty-one patients (mean age 52 +/- 2 yr) undergoing gynecologic (46%), orthopedic (44%), or other (10%) surgery were recruited. Cumulative 24-hr morphine consumption was not different between the four groups, but pain scores at rest and on movement were significantly higher in the 2 mg nabilone group compared to the other groups. There were no significant differences between groups with respect to episodes of nausea and vomiting, quality of sleep, sedation, euphoria, pruritus, or the number and severity of adverse events. No serious adverse event was recorded.

CONCLUSIONS

Contrary to the main hypothesis, high dose nabilone in the presence of morphine patient controlled analgesia is associated with an increase in pain scores in patients undergoing major surgery.

Formulation considerations for the development of medications with abuse potential

The availability of increasingly sophisticated drug formulations and delivery devices has created new opportunities in drug development. These newer approaches can result in improved drug bioavailability, or they can alter key pharmacokinetic parameters in such a way as to decrease dosing interval, decrease variability, or blunt maximal concentrations that are associated with adverse events of particular concern. Special formulations or devices can also provide for easier or more convenient dosing in subpopulations of interest, such as children or the elderly. Although the key principles of abuse potential assessment and the underlying neurochemistry and pharmacology are relatively well understood, evaluation of the influences of drug formulation have received much less study. Because dose and formulation - and even the therapeutic indication - are refined over the course of development, it is usually difficult to conduct more than a cursory evaluation of the influence of formulation on the underlying abuse potential of the active pharmaceutical ingredient. Industrial sponsors would benefit from further research in areas of formulation science and pharmacokinetics that would improve the predictability of prescription drug abuse. In particular, validation of new pharmacokinetic parameters and standardization of methods to understand the consequences of product tampering could assist in gaining a better assessment of risk for controlled release formulations. Such methods could apply not only to innovator products, but also to those wishing to develop generic versions with similar pharmaceutical performance. This article proposes several factors that may be of use to industrial sponsors in making formulation choices for drugs with the potential for abuse.

The marijuana withdrawal syndrome: diagnosis and treatment

A subset of marijuana smokers develop a cannabis use disorder and seek treatment for their marijuana use on their own initiative. A less well-known consequence of daily, repeated marijuana use is a withdrawal syndrome, characterized by a time-dependent constellation of symptoms: irritability, anxiety, marijuana craving, decreased quality and quantity of sleep, and decreased food intake. Treatment studies show that rates of continuous abstinence are low (comparable to relapse rates for other abused drugs), and more treatment options are needed. The objective of this review is to update clinicians on the current state of marijuana research and to describe features of marijuana withdrawal to facilitate the diagnosis and treatment of cannabis use disorders.

Self-administration of cannabinoids by experimental animals and human marijuana smokers

Drug self-administration behavior has been one of the most direct and productive approaches for studying the reinforcing effects of psychoactive drugs, which are critical in determining their abuse potential. Cannabinoids, which are usually abused by humans in the form of marijuana, have become the most frequently abused illicit class of drugs in the United States. The early elucidation of the structure and stereochemistry of delta-9-tetrahydrocannabinol (THC) in 1964, which is now recognized as the principal psychoactive ingredient in marijuana, activated cannabinoid research worldwide. This review examines advances in research on cannabinoid self-administration behavior by humans and laboratory animals. There have been numerous laboratory demonstrations of the reinforcing effects of cannabinoids in human subjects, but reliable self-administration of cannabinoids by laboratory animals has only recently been demonstrated. It has now been shown that strong and persistent self-administration behavior can be maintained in experimentally and drug-naïve squirrel monkeys by doses of THC comparable to those in marijuana smoke inhaled by humans. Furthermore, reinforcing effects of some synthetic CB1 cannabinoid agonists have been recently reported using intravenous and intracerebroventricular self-administration procedures in rats and mice. These findings support previous conclusions that THC has a pronounced abuse liability comparable to other drugs of abuse under certain experimental conditions. Self-administration of THC by squirrel monkeys provides the most reliable animal model for human marijuana abuse available to date. This animal model now makes it possible to study the relative abuse liability of other natural and synthetic cannabinoids and to preclinically assess new therapeutic strategies for the treatment or prevention of marijuana abuse in humans.

Reinforcing effects of oral Delta9-THC in male marijuana smokers in a laboratory choice procedure

RATIONALE

Oral Delta-9-tetrahydrocannabinol (Delta(9)-THC; Marinol) is medically available for the treatment of nausea associated with cancer chemotherapy and for wasting syndromes related to HIV/AIDS. Little is known about its reinforcing effects.

OBJECTIVE

This study was conducted to characterize the reinforcing effects of oral Delta(9)-THC in experienced marijuana smokers under controlled laboratory conditions.

METHODS

Ten healthy male marijuana users completed this 17-day residential study. On days 2, 6, 10, and 14, at 0900 h, participants received a "sample" oral dose of Delta(9)-THC (0, 10, 20 mg) and an alternative reinforcer, a 2 US dollars voucher (redeemable for cash at study's end). Over the next 3 days, they had 11 opportunities to self-administer either the sampled dose of Delta(9)-THC or to receive a 2 US dollars voucher.

RESULTS

Participants chose active Delta(9)-THC (10 and 20 mg) more often than placebo (<two selections vs approximately four selections, respectively). However, they chose active Delta(9)-THC on less than 50% of choice opportunities. Both active Delta(9)-THC doses produced significant increases in "positive" subjective effects, impaired psychomotor performance, and increased heart rate, relative to the placebo conditions.

CONCLUSION

These data indicate that oral Delta(9)-THC may have modest abuse liability in experienced marijuana smokers.

Naltrexone reduces the relative reinforcing value of nicotine in a cigarette smoking choice paradigm

RATIONALE

Human behavioral pharmacology studies can examine how medications that target different neurotransmitter systems influence different aspects of smoking. Naltrexone and bupropion have been shown to alter ad lib smoking behavior; however, medication effects on nicotine reward in a cigarette choice paradigm have yet to be investigated.

OBJECTIVE

This study explored the effects of an acute dose of naltrexone, bupropion, or placebo on the relative reinforcing value of nicotine from cigarette smoking using new nicotine and de-nicotinized (Quest, 0.6 and 0.05 mg = "denicotinized") cigarettes.

METHODS

In a double-blind, within-subjects design, 26 dependent smokers participated in three experimental cigarette smoking sessions following pretreatment with either naltrexone (50 mg), bupropion (300 mg), or placebo. After medication administration and 2 h of monitored deprivation from cigarettes and food, participants rated their responses to the initial exposure to the cigarettes and then participated in four choice sessions over a 2-h period during which they could take four puffs from either cigarette.

RESULTS

The relative reinforcing value of nicotine, as measured by the number of nicotine puffs chosen out of 16, was significantly lower following naltrexone compared to placebo. There were no effects of an acute dose of bupropion on nicotine choices.

CONCLUSIONS

These results suggest that naltrexone may reduce the relative reinforcing effects of nicotine via cigarette smoking and support ongoing investigation of opioid antagonists as potential smoking cessation pharmacotherapies.

Effects of oral THC maintenance on smoked marijuana self-administration

Studies have shown that the Delta(9)-tetrahydrocannabinol (Delta(9)-THC) concentration in marijuana cigarettes is an important factor for the maintenance of marijuana self-administration. Yet, the impact of oral Delta(9)-THC treatment on marijuana self-administration is unknown. Because other agonist therapies have been demonstrated to be effective for the treatment of substance use disorders, the objective of this study was to evaluate the influence of oral Delta(9)-THC maintenance on choice to self-administer smoked marijuana. During this 18-day residential study, 12 healthy research volunteers received one of three doses of oral Delta(9)-THC capsules (0, 10, 20 mg q.i.d.) for 3 consecutive days, followed by 3 consecutive days of matching placebo. The order of active Delta(9)-THC administration was counterbalanced. Each morning, except on days 6, 12, and 18, participants smoked the 'sample' marijuana cigarette (1.8% Delta(9)-THC w/w) and received a $2 voucher (redeemable for cash at study's end). Following the sample, volunteers participated in a four-trial choice procedure during which they had the opportunity to self-administer either the dose of marijuana they sampled that morning or to receive the $2 voucher. Relative to placebo Delta(9)-THC maintenance, participants' choice to self-administer marijuana was not significantly altered by either of the two active Delta(9)-THC maintenance conditions. Some 'positive' subjective drug-effect ratings following the sample marijuana cigarette were reduced: by day 3 of active oral Delta(9)-THC maintenance, participants' rating of 'Good Drug Effect' and 'High' were significantly decreased. Smoked marijuana-related total daily caloric intake was not significantly altered under any maintenance conditions. Finally, the effects of smoked marijuana on psychomotor task performance were only minimally affected by oral Delta(9)-THC maintenance. These data indicate that participants' choice to self-administer marijuana was unaltered by the oral Delta(9)-THC dosing regimen used in the present investigation.

Acute nicotine reinforcement, but not chronic tolerance, predicts withdrawal and relapse after quitting smoking

Little research has examined the association of tobacco dependence with nicotine tolerance or reinforcement in a clinical sample. Smokers preparing to quit smoking participated in laboratory sessions to assess nicotine tolerance on subjective, cardiovascular, and performance measures and to assess nicotine reinforcement using a choice procedure. Participants were then provided with individual counseling (but no medication), made a quit attempt, and were followed for 1 year to determine clinical outcome, as determined by postquit withdrawal and days to relapse. Nicotine tolerance was unrelated to either withdrawal or relapse. However, acute nicotine reinforcement was significantly related to both greater withdrawal and faster relapse. Results challenge the common assumption that nicotine tolerance is closely related to dependence but suggest that nicotine reinforcement may have theoretical and clinical significance for dependence.

Marijuana use among adolescents

More than half of US adolescents will experiment with marijuana. Of those who try marijuana more than once, approximately one third will subsequently use marijuana regularly, although most will have stopped by their late 20s. Although genetic predisposition plays the most important role in determining who will develop dependence, environmental factors influence who will initiate marijuana use. One of the challenges for prevention and treatment programs is that the immediate adverse effects of marijuana use are not extreme, and many adolescents have difficulty in making decisions based on future risks. Therefore, the consequences of leaving school early, having unprotected sex, and driving while intoxicated are often insufficient to deter adolescents from using marijuana. Thus, it is not surprising that current prevention and treatment programs have had limited success in decreasing the rates of initiation and regular use of marijuana among adolescents. However, the accumulation of data about marijuana use in adolescents has the potential to enable the development of more effective prevention and treatment programs.

Nicotine preference in smokers as a function of smoking abstinence

Overnight smoking abstinence increases desire to smoke and intensity of smoking behavior in smokers, but it is not completely clear that this reflects an increase in reinforcement from the psychoactive effects of nicotine per se. We examined choice of nicotine vs. placebo via nasal spray (Study 1) and nicotine vs. nonnicotine cigarette puffs (Study 2) in separate groups of smokers during each of two sessions, following overnight abstinence vs. no abstinence. In each study, subjects followed a forced choice procedure in which they were instructed to self-administer six sprays/puffs from between the two nasal sprays/cigarettes every 15 min for 2 h following initial exposure to each. In Study 1, choice of nicotine spray (1.5 micrograms/kg per spray) increased significantly following abstinence vs. no abstinence (47 +/- 6% vs. 34 +/- 5%, respectively, p < 0.05). This shift in choice was more pronounced in the subset of smokers (choosers, n = 9 out of 24) who selected nicotine on more than 50% of choices on the abstinent day. Choosers exhibited greater responses to initial nicotine exposure on positive (e.g., pleasant, vigor) but not aversive (e.g., jittery, uneasy) subjective measures, suggesting that greater positive reinforcement from nicotine per se predicted subsequent choice. In Study 2, abstinence similarly increased choice of nicotine vs. nonnicotine cigarette puffs (82 +/- 6% vs. 64 +/- 8%, p < 0.05), although nearly all subjects (12 of 13) preferred the nicotine cigarette following abstinence. These results indicate that choice of nicotine per se, isolated from tobacco smoke, increases significantly after overnight tobacco abstinence.