We examined the effects of oral caffeine on cigarette smoking and subjective response in a group of six smokers who smoked cigarettes ad libitum in a naturalistic laboratory environment. A within-subject, repeated-measures design was used, and each subject received placebo, caffeine base (50 to 800 mg), or d-amphetamine sulfate (25 mg) on several occasions before 90-min daily smoking sessions. There was no evidence of an increase in the number of cigarettes smoked or the amount of smoke inhaled per session after caffeine. Caffeine increased salivary caffeine concentrations, arm tremor, and self-reported measures of mood and subjective response. The major subjective effects of caffeine were increases in tension-anxiety and dysphoric-somatic effects. In contrast, d-amphetamine induced increases in the number of cigarettes smoked and in the amount of smoke inhaled per session. The major subjective effects of 25 mg of d-amphetamine were increases in measures of well-being, euphoria, and mental efficiency. Results demonstrate that caffeine and d-amphetamine have different effects on cigarette-smoking behavior as well as on subjective response and suggest that the positive correlation between cigarette smoking and coffee drinking is not the result of a simple pharmacologic effect of caffeine.

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.

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.

The reinforcing and subjective effects of phenylpropanolamine (PPA, 25 and 75 mg, PO) were compared with those of d-amphetamine (AMP, 5 mg) in a group of normal, healthy adults (eight males, nine females) with no history of drug abuse. A discrete-trial choice procedure was used in which subjects first sampled placebo and a dose of one of the drugs. Subjects were then allowed to choose between self-administration of drug or placebo on three separate occasions. The relative frequency with which active drug was chosen over placebo was used as the primary index of the drug's reinforcing efficacy. Subjective effects were measured with the Profile of Mood States, a short version of the Addiction Research Center Inventory and a series of visual analog scales. Ratings of drug liking, drug labelling, general activity level and strength of drug preference were also obtained. As expected, AMP was chosen significantly more often than expected by chance (69% of occasions). AMP also increased ratings of drug liking, preference strength, and activity level, and produced a profile of subjective effects consistent with its well-established stimulant and euphorigenic properties. The low dose of PPA was without effect on most measures. PPA 75 mg was chosen significantly less often than expected by chance (39% of occasions). This dose of PPA was most frequently labelled as a stimulant, and produced significant increases on ratings of Anxiety and "stimulated," and decreases on ratings of "sedated" and "hungry." Unlike AMP, PPA did not affect ratings of drug liking or mood scales reflecting euphoria. In sum, these results indicate that PPA does not possess AMP-like dependence potential.