Acute and residual effects of marijuana: profiles of plasma THC levels, physiological, subjective, and performance measures

Three experienced marijuana smokers participated in four 2-day experimental sessions in which they smoked either 0, 1, or 2 marijuana cigarettes containing 2.57% delta 9-tetrahydrocannabinol (THC) at two different times on the first day. A battery of physiological, subjective, and performance measures was repeated throughout day 1 to assess acute effects and on day 2 to measure any residual effects of marijuana. Blood samples were also repeatedly collected to examine the relationship between plasma levels and pharmacological effects of THC. Acutely, marijuana increased heart rate and subjective ratings of drug effects and slightly impaired performance on a circular lights task in all subjects. Performance was also impaired (decreased accuracy and increased response time) on serial addition/subtraction and digit recall tasks on day 1 in two subjects. On day 2, tachycardia and subjective effects of marijuana were not observed. Performance remained impaired on the arithmetic and recall tasks on day 2, although the decrements were not as large as those observed on day 1. In general, plasma THC levels covaried with the other measures. These preliminary results suggest that marijuana can adversely affect complex human performance up to 24 hours after smoking.     

Effects of tetrahydrocannabinol content on marijuana smoking behavior, subjective reports, and performance

This study investigated the smoking topography of marijuana and its effect on heart rate, subjective reports, and cognitive/psychomotor task performance. Male subjects (N = 12) with histories of moderate marijuana use smoked ad lib one cigarette containing 0, 1.3, or 2.7% delta 9-THC on separate days. Smoking topography measures revealed smaller puff and inhalation volumes and shorter puff duration for the high marijuana dose compared to the low dose. No other smoking behavior differed between the active doses. Heart rate was increased dose dependently over placebo levels. Active marijuana also increased subjective reports of drug effect over placebo, but not dose dependently. Significant memory impairment was observed on a forward and reverse digit span task, and performance was impaired on the digit symbol substitution task by the high, but not low, dose of marijuana. Performance on a divided attention task was not affected by marijuana. Thus, although subjects adjusted their smoking of cigarettes varying in THC content, dose-related effects of marijuana were obtained on several measures. The observed differences and individual variation in smoking topography measures suggest that precise control of smoking behavior would improve the accuracy of marijuana dose delivery.     

Repeated administration of the D1/5 antagonist ecopipam fails to attenuate the subjective effects of cocaine

RATIONALE: Dopaminergic compounds have been targeted as potential treatments for cocaine abuse because of the known role of dopamine systems in drug reinforcement. Recent preclinical and human data have focused on the D1/5 antagonist, SCH 39166 (ecopipam), as a potential therapeutic agent. OBJECTIVES: The objective of the present study was to determine whether treatment with chronic ecopipam can blunt or block the subjective effects of cocaine in the absence of significant behavioral impairment or toxic physiological effects. METHODS: Four doses of ecopipam (0, 10, 25, and 100 mg p.o.) were administered daily for 1 week each in double-blind, random order to inpatient cocaine-dependent volunteers (n = 10). Cocaine challenge doses (0, 25, and 50 mg/70 kg i.v.) were administered on the 7th day in ascending order, 1 h apart. RESULTS: Ecopipam alone produced reliable dose-dependent deficits in performance on the digit symbol substitution task (DSST) and the circular lights task, but not a balance task. Impairment on the DSST waned with repeated dosing suggesting the development of tolerance. Ecopipam resulted in few direct subjective effects. Cocaine alone produced dose-dependent changes in prototypic subjective and physiological measures, however, ecopipam largely failed to alter either cocaine's direct effects or the desire for cocaine. CONCLUSIONS: Although the performance effects verify that these doses of ecopipam were behaviorally active, the absence of an attenuation of cocaine's effects of craving for cocaine in this chronic dosing paradigm suggests this compound is unlikely to be an effective pharmacotherapy for cocaine abuse.     

Acute and residual effects of alcohol and marijuana,alone and in combination,on mood and performance

The duration of behavioral impairment after marijuana smoking remains a matter of some debate. Alcohol and marijuana are frequently used together, but there has been little study of the effects of this drug combination on mood and behavior the day after use. The present study was designed to address these issues. Fourteen male and female subjects were each studied under four conditions: alcohol alone, marijuana alone, alcohol and marijuana in combination, and no active treatment. Mood and performance assessments were made during acute intoxication and twice the following day (morning and mid-afternoon). Acutely, each drug alone produced moderate levels of subjective intoxication and some degree of behavioral impairment. The drug combination produced the greatest level of impairment on most tasks and strong overall subjective ratings. There were few significant interactions between the two drugs, indicating that their effects tended to be additive. Only weak evidence was obtained for subjective or behavioral effects the day after active drug treatments, although consistent time-of-day effects (morning versus afternoon) were observed on several subjective and behavioral measures. In sum, this study provided little evidence that moderate doses of alcohol and marijuana, consumed either alone or in combination, produce behavioral or subjective impairment the following day.     

Separate and combined effects of marijuana and alcohol on mood,equilibrium and simulated driving

Abstract Rationale . Marijuana and alcohol, when used separately and in combination, contribute to automobile accidents and failed sobriety tests of standing balance. However, the extent to which the drugs have additive effects on both of these measures is unknown. Objectives . This study was designed to compare directly the separate and combined effects of marijuana and alcohol on simulated emergency braking and dynamic posturography. Methods. Twelve healthy subjects who regularly used both marijuana and alcohol completed nine test sessions in a counterbalanced within-subject design. Subjects drank a beverage (0, 0.25, or 0.5 g/kg alcohol) then smoked a cigarette (0, 1.75, or 3.33% THC). Testing began 2 min after smoking and was conducted within the ascending limb of the blood alcohol curve. Results. The 0.5 g/kg alcohol dose significantly increased brake latency without affecting body sway. In contrast, the 3.3% THC dose increased body sway but did not affect brake latency. There were no additive drug effects on mood or behavior. Conclusions . Although field sobriety tests are often used to determine driving impairment, these results suggest that impaired balance following marijuana use may not coincide with slowed reaction time. Conversely, braking impairment from low doses of alcohol may not be revealed by tests of balance. Electronic Publication     

Effects of alcohol on psychomotor performance and perceived impairment in heavy binge social drinkers

Alcohol intoxication often results in negative consequences; however, specific behavioral and subjective effects vary as a function of individual differences. The present study utilized an alcohol challenge paradigm to examine whether heavy binge social drinkers (HD; n=77), compared to light social drinkers (LD; n=55), exhibit: (1) greater tolerance in psychomotor task performance under the influence of alcohol, and (2) differential perceptions of the impairing effects of alcohol. The study included three test sessions in which participants consumed either a low (0.4 g/kg) or a high (0.8 g/kg) dose of ethanol or a placebo beverage administered in random order and counterbalanced within group. Participants completed the Digit-Symbol Substitution Task (DSST) and the Grooved Pegboard at pre-drink baseline and at multiple time points after beverage consumption. They also completed a scale of perceived impairment at several intervals after beverage consumption. Ethanol impaired performance at the high dose, but not at the low dose (ps<.001). The groups exhibited similar alcohol-induced impairment. However, HD reported lower self-perceived impairment compared to LD, particularly during the early portion of the blood alcohol curve when actual impairment was most pronounced (p<.001). Thus, this study extends prior research in that habitual binge social drinking does not appear to be associated with tolerance to alcohol's impairing effects on select psychomotor skills. Further, results may have implications for alcohol-related harm as binge social drinkers regularly consume intoxicating doses of alcohol but may not be aware of the physical and cognitive impairments produced by alcohol.     

Effects of marijuana smoking on subjective ratings and tobacco smoking

Multiple measures of tobacco cigarette smoking and subjective and physiological effect were collected during 90 minute test sessions in volunteer cigarette smokers who also had histories of recreational marijuana use. Before sessions, subjects smoked one marijuana cigarette (placebo or 1.29%, 2.84%, 4.00%) using a standardized puffing procedure. Each dose and placebo was given four times to each subject in a randomized block sequence. Marijuana smoking produced dose-related increases in heart rate, ratings of dose strength and drug liking. However, marijuana produced no significant alterations in tobacco cigarette smoking. Puff duration within each marijuana cigarette varied in a fashion similar to that observed in previous studies of tobacco cigarette smoking: puff duration progressively decreased as the cigarette was smoked. This effect is probably due to progressive decreases in resistance to draw as the cigarette is smoked. Expired air carbon monoxide (CO) levels following marijuana smoking were inversely related to marijuana dose, suggesting the occurrence of some compensatory changes in marijuana smoking in response to dose manipulations. It is concluded that, although marijuana produces dose-related effects on physiological and subjective effects and on marijuana smoking behavior, marijuana differs from a variety of other psychoactive drugs previously studied in this paradigm in that no reliable changes in tobacco smoking were produced.     

Marijuana,alcohol and actual driving performance

The objective of the current study was to assess the separate and combined effects of marijuana and alcohol on actual driving performance. Eighteen subjects were treated with drugs and placebo according to a balanced, 6-way, crossover design. On separate evenings they were given weight calibrated Delta(9)-tetrahydrocannabinol (THC) doses of 0, 100 and 200 &mgr;g/kg with and without an alcohol dose sufficient for achieving blood alcohol concentrations (BAC) of 0.04 g/dl while performing a Road Tracking and Car Following Test in normal traffic. Main outcome measures were standard deviation of lateral position (SDLP), time driven out of lane (TOL), reaction time (RT) and standard deviation of headway (SDH). Both THC doses alone, and alcohol alone, significantly impaired the subjects performances in both driving tests. Performance deficits were minor after alcohol and moderate after both THC doses. Combining THC with alcohol dramatically impaired driving performance. Alcohol combined with THC 100 and 200 &mgr;g/kg produced a rise in SDLP the equivalent of that associated with BAC=0.09 and 0.14 g/dl, respectively. Mean TOL rose exponentially with SDLP. Relative to placebo mean RT lengthened by 1.6 s under the combined influence of alcohol and THC 200 &mgr;g/kg. Changes in SDH ranged between 0.9 and 3.8 m. Low doses of THC moderately impair driving performance when given alone but severely impair driving performance in combination with a low dose of alcohol. Copyright 2000 John Wiley & Sons, Ltd.     

Effects of alcohol pretreatment on human marijuana self-administration

Alcohol and marijuana are frequently used together, yet there has been little study of how the presence of one drug might affect consumption of the other. The present study examined the effects of alcohol pretreatments on marijuana self-administration in a group of 15 males and 5 females who were users of both drugs. During evening sessions in a recreational setting, pairs of subjects consumed drinks containing 0.0, 0.3 or 0.6 g/kg alcohol 30 min before a 60-min period of ad libitum marijuana smoking. Marijuana self-administration was assessed in several ways: by measuring the number of cigarettes smoked, the increase in expired air carbon monoxide resulting from marijuana smoke inhalation, and the increase in heart rate due to THC absorption. None of these variables was significantly affected by the alcohol pretreatments, although substantial individual differences were observed. These results indicate that low to moderate doses of alcohol do not systematically influence marijuana self-administration.     

Acute and Residual Effects of Marijuana in Humans

Marijuana continues to be the most commonly abused illicit drug in the United States. Because many people abuse marijuana during the evening and on weekends and then go to work or school the next day, more research is needed on the residual effects of marijuana. The current study sought to examine both acute and residual subjective, physiologic, and performance effects of smoking a single marijuana cigarette. Ten healthy male volunteers who reported recent use of marijuana resided on a residential research ward. On three separate days, subjects smoked one NIDA marijuana cigarette containing either 0%, 1.8%, or 3.6% Δ⁹-tetrahydrocannabinol (THC) according to a paced puffing procedure. Subjective, physiologic, and performance measures were collected prior to smoking, five times following smoking on that day, and three times on the following morning. Subjects reported robust subjective effects following both active doses of marijuana, which returned to baseline levels within 3.5 h. Heart rate increased and the pupillary light reflex decreased following active dose administration with return to baseline on that day. A new finding was that marijuana smoking acutely produced decrements in smooth pursuit eye tracking. Although robust acute effects of marijuana were found on subjective and physiological measures, and on smooth pursuit eye tracking performance, no effects were evident the day following administration, indicating that the residual effects of smoking a single marijuana cigarette are minimal.     

Effects of food deprivation on responses to marijuana in humans

The effects of 24h of food deprivation on subjective, physiological and cognitive responses to marijuana were studied in 8 male marijuana smokers. A within-subjects design was used in which subjects smoked active (1.3% THC) and placebo (0.0% THC) marijuana in both a fed and a fasting state. Each of the four experimental conditions - Fed/Active, Fed/Placebo, Fast/Active, Fast/Placebo - was enacted twice according to a randomized block design. A controlled smoking regimen was employed which held inhaled volume of marijuana smoke constant across feeding conditions. Smoke inhalation was monitored by measuring expired-air carbon monoxide (CO) levels before and after smoking. Heart rate and subjective effects of marijuana were assessed before, during and after smoking. A measure of memory performance, free recall, was also assessed after smoking. CO absorption from both placebo and active marijuana did not differ across feeding conditions, indicating that smoke dose was similar across feeding conditions. Typical effects of marijuana, such as elevated heart rate, impaired memory and increased "high" ratings were obtained after smoking active marijuana, but fasting had no effect on the drug response. Lack of a food deprivation effect on marijuana subjective effects and memory performance was noted not only in all subjects, but also in a subset of subjects (n=6) whose physiological states provided verification of their fasting state in Fast sessions.     

Acute effects of smoking marijuana on hormones, subjective effects and performance in male human subjects

Four healthy male subjects smoked two marijuana cigarettes or one marijuana cigarette and one placebo cigarette, or two placebo cigarettes on separate days in a random order crossover design. Each marijuana cigarette contained 2.8% delta-9-tetrahydrocannabinol (THC). Plasma hormones and THC were measured before and after each smoking session. Plasma LH was significantly depressed and cortisol was significantly elevated after smoking marijuana. Nonsignificant depressions of prolactin, FSH, testosterone and free testosterone and elevation of GH also occurred. Concurrent measures of subjective effects via subscales of the Addiction Research Center Inventory, Single Dose Questionnaire and a Visual Analog Scale were generally elevated. Significant impairment on a psychomotor performance task paralleled elevations in subjective effects, hormone effects and peak THC determinations. Although all the hormone effects were within normal basal ranges, interactions between these systems, and their effects on behavior cannot be discounted.     

Reinforcing and subjective effects of oral Δ9-THC and smoked marijuana in humans

The reinforcing and subjective effects of oral delta-9-tetrahydrocannabinol (THC) and smoked marijuana were studied in two groups of regular marijuana users. One group (N=10) was tested with smoked marijuana and the other (N=11) with oral THC. Reinforcing effects were measured with a discrete-trial choice procedure which allowed subjects to choose between the self-administration of active drug or placebo on two independent occasions. Subjective effects and heart rate were measured before and after drug administration. Smoked active marijuana was chosen over placebo on both choice occasions by all subjects. Similarly, oral THC was chosen over placebo on both occasions by all but one subject. Both active drug treatments produced qualitatively and quantitatively similar subjective effects, and both significantly increased heart rate, although the time course of effects differed substantially between the two treatments. The results demonstrate that both smoked marijuana and oral THC can serve as positive reinforcers in human subjects under laboratory conditions. The experimental paradigm used here should prove useful for identifying factors that influence the self-administration of marijuana and other cannabinoids by humans.     

Comparison of the subjective effects of Δ<Superscript>9</Superscript>-tetrahydrocannabinol and marijuana in humans

RATIONALE: There has been controversy about whether the subjective, behavioral or therapeutic effects of whole plant marijuana differ from the effects of its primary active ingredient, Delta(9)-tetrahydrocannabinol (THC). However, few studies have directly compared the effects of marijuana and THC using matched doses administered either by the smoked or the oral form.OBJECTIVE: Two studies were conducted to compare the subjective effects of pure THC to whole-plant marijuana containing an equivalent amount of THC in normal healthy volunteers. In one study the drugs were administered orally and in the other they were administered by smoking.METHODS: In each study, marijuana users (oral study: n=12, smoking study: n=13) participated in a double-blind, crossover design with five experimental conditions: a low and a high dose of THC-only, a low and a high dose of whole-plant marijuana, and placebo. In the oral study, the drugs were administered in brownies, in the smoking study the drugs were smoked. Dependent measures included the Addiction Research Center Inventory, the Profile of Mood States, visual analog items, vital signs, and plasma levels of THC and 11-nor-9-carboxy-THC.RESULTS: In both studies, the active drug conditions resulted in dose-dependent increases in plasma THC levels, and the levels of THC were similar in THC-only and marijuana conditions (except that at the higher oral dose THC-only produced slightly higher levels than marijuana). In both the oral study and the smoking study, THC-only and whole plant marijuana produced similar subjective effects, with only minor differences.CONCLUSION: These results support the idea that the psychoactive effects of marijuana in healthy volunteers are due primarily to THC.     

Differential response to alcohol in light and moderate female social drinkers

Individuals who are moderate drinkers are at increased risk to abuse alcohol. Moreover, women are more vulnerable than men to the adverse consequences of alcohol consumption and recent data indicate that the drinking pattern in women is becoming more similar to that of men. However, few studies have determined whether female moderate drinkers (MD) show a differential response to the subjective and performance effects of alcohol, compared to female light drinkers (LD). Fifteen female MD who consumed an average of 34.7 drinks/month were compared to 15 female LD who consumed an average of 6.7 drinks/month. None of the participants had a first-degree family history of alcoholism or substance abuse. The acute effects of alcohol (0, 0.25, 0.50, 0.75 mg/kg) were evaluated using a double-blind, placebo-controlled outpatient design. Drug effects were assessed using a full range of performance measures, subjective-effects questionnaires and observer ratings. Alcohol impaired performance in a dose-related manner on all performance tasks for both groups of females. However, MD were less impaired than LD on balance and Digit Symbol Substitution Test (DSST). This reduced response was also evident from the observer ratings, with MD being viewed as less impaired by alcohol than LD. While ratings of Drug Liking increased in both groups of women on the ascending limb of the breath alcohol curve, alcohol was disliked by LD on the descending limb and LD reported increased ratings of Bad Drug Effects following the high dose of alcohol. The reduced performance impairment, coupled with the positive subjective effects and relative absence of adverse subjective effects, suggestive of behavioral tolerance, could result in a progression towards increased alcohol consumption among moderate female social drinkers.     

Acute behavioral and cardiac effects of cocaine and alcohol combinations in humans

Subjects received acute doses of orally administered alcohol (0–1.0 g/kg) and intranasal cocaine (4–96 mg/70 kg) alone and in combination in two experiments. Results generally were consistent across both experiments. Cocaine administered alone improved Digit Symbol Substitution Test (DSST) performance, increased subject ratings of stimulant-like effects, heart rate and blood pressure, and decreased skin temperature. Alcohol administered alone disrupted DSST performance, increased ratings of drunkenness, heart rate and skin temperature, and decreased blood pressure. Combining cocaine and alcohol attenuated the disruptions in DSST performance observed with alcohol alone, and either did not change or attenuated the improvements in performance observed with cocaine alone. Combining the drugs also attenuated effects observed with the drugs alone on skin temperature and, to a lesser extent, blood pressure. By contrast, drug combinations increased heart rate above levels observed when cocaine or alcohol were administered alone. Effects of the drug combinations on subject ratings were variable.     

The effects of repeated doses of temazepam taken in conjunction with alcohol on aspects of psychomotor performance the morning following night time medication.

A study to compare the morning-after effects of three dose levels of temazepam (Euhypnos capsules) given with alcohol, was carried out in 18 healthy volunteers. Matched placebos were given for two days before and four days after the four nights on active drug and a standard dose of alcohol was given on all ten nights of the study. Objective measurements made on the mornings after days 2, 4, 6 and 10 were critical flicker fusion threshold (CFF), choice reaction time (CRT) and digit symbol substitution tasks (DSST). The administration of 10 or 20 mg temazepam with alcohol produced no significant change inany of these measurements. 30 mg produced no change in DSST and although there was some impairment of CRT at this dose, it was not statistically significant. The combination of 30 mg temazepam and alcohol significantly depressed CFF following four nights on these drugs.     

Comparison of smoked marijuana and oral Δ<Superscript>9</Superscript>-tetrahydrocannabinol in humans

Abstract Rationale. Although smoked marijuana contains at least 60 cannabinoids, Δ⁹-tetrahydrocannabinol (Δ⁹-THC) is presumed to be the cannabinoid primarily responsible for many marijuana-related effects, including increased food intake and subjective effects. Yet, there has been no systematic comparison of repeated doses of oral Δ⁹-THC with repeated doses of smoked marijuana in the same individuals. Objective. To compare the effects of oral Δ⁹-THC and smoked marijuana in humans under controlled laboratory conditions. Methods. Eleven healthy research volunteers, who reported smoking an average of six marijuana cigarettes per day, completed an 18-day residential study. Marijuana cigarettes (3.1% Δ⁹-THC, q.i.d.) were smoked or Δ⁹-THC (20 mg, q.i.d.) was taken orally using a staggered, double-blind, double-dummy procedure for three consecutive days. Four days of placebo administration separated each active drug condition. Psychomotor task performance, subjective effects, and food intake were measured throughout the day. Results. Relative to placebo baseline, oral Δ⁹-THC and smoked marijuana produced similar subjective-effect ratings (e.g., "high" and "mellow"), although some effects of smoked marijuana were more pronounced and less prone to the development of tolerance. Additionally, participants reported "negative" subjective effects (e.g., "irritable" and "miserable") during the days after smoking marijuana but not after oral Δ⁹-THC. Both drugs increased food intake for 3 days of drug administration, but had little effect on psychomotor performance. Conclusion. These results indicate that the behavioral profile of effects of smoked marijuana (3.1% Δ⁹-THC) is similar to the effects of oral Δ⁹-THC (20 mg), with some subtle differences. Electronic Publication     

Behavioral and subjective effects of marijuana following partial sleep deprivation

This study tested whether performance would be more impaired when marijuana use followed partial sleep deprivation (PSD) than when marijuana use followed a typical night of sleep. Seven recreational marijuana users (mean 15 of last 30 days) completed six test sessions in a double-blind randomized within-subject design. Each session began with an overnight stay in a sleep laboratory. Bed and wake times were calculated from mean data on individual sleep diaries. Time-in-bed was either regular (mean=8.2 h) or shortened (first 65% of regular time-in-bed deprived). At 3 and 5 h after waking, daytime sleepiness was measured with self-report questionnaires and a sleep latency test. Approximately 6.5 h after waking, subjects smoked a marijuana cigarette (0.003, 2, or 3.5% delta-9 tetrahydrocannabinol [THC]). Test batteries were completed 2, 62, and 122 min after smoking ended. Sleepiness was significantly greater following PSD than after regular sleep. Following regular sleep, heart rate increases with active THC doses were comparable, but heart rate with 2% THC was significantly less elevated following PSD. Ratings of ‘impaired’ and ‘stoned’ increased with both THC doses after regular sleep and were further increased with 3.5% THC after PSD. High-potency marijuana increased body sway similarly across sleep conditions. There were no significant effects of marijuana or PSD, alone or in combination, on brake latency. Thus, while PSD increased the dose-dependence of THC effects on heart rate and subjective impairment, it did not enhance the effects of marijuana on standing balance and brake latency.     

A study investigating the acute dose-response effects of 13 mg and 17 mg Delta 9- tetrahydrocannabinol on cognitive-motor skills, subjective and autonomic measures in regular users of marijuana

Heavy use of marijuana is claimed to damage critical skills related to short-term memory, visual scanning and attention. Motor skills and driving safety may be compromised by the acute effects of marijuana. The aim of this study was to investigate the acute effects of 13 mg and 17 mg Delta 9-tetrahydrocannabinol (THC) on skills important for coordinated movement and driving and on subjective and autonomic measures in regular users of marijuana. Fourteen regular users of marijuana were enrolled. Each subject was tested on two separate days. On each test day, subjects smoked two low-nicotine cigarettes, one with and the other without THC. Seventeen mg THC was included in the cigarette on one test day and 13 mg on the other day. The sequence of cigarette types was unknown to the subject. During smoking, heart rate and blood pressure were monitored, and the subjects performed a virtual reality maze task requiring attention and motor coordination, followed by 3 other cognitive tasks (Wisconsin Card Sorting Test (WCST), a "gambling" task and estimation of time and distance from an approaching car). After smoking a cigarette with 17 mg THC, regular marijuana users hit the walls more often on the virtual maze task than after smoking cigarettes without THC; this effect was not seen in patients after they smoked cigarettes with 13 mg THC. Performance in the WCST was affected with 17 mg THC and to a lesser extent with the use of 13 mg THC. Decision making in the gambling task was affected after smoking cigarettes with 17 mg THC, but not with 13 m THC. Smoking cigarettes with 13 and 17 mg THC increased subjective ratings of pleasure and satisfaction, drug "effect" and drug "high". These findings imply that smoking of 17 mg THC results in impairment of cognitive-motor skills that could be important for coordinated movement and driving, whereas the lower dose of 13 mg THC appears to cause less impairment of such skills in regular users of marijuana.