Marijuana use has increased and is widespread, particularly among teenagers and young adults. Research during the past year underscores the necessity of taking into account multiple aspects of the individual and the drug taking situation in evaluating marijuana's effects. These include such varied aspects as the characteristics of the material itself, the dose and route of administration, the individual's metabolic rate, prior experience with the drugs, the user's set (personal expectations), and the setting in which the drug is used. Experienced users report such subjective effects as an awareness of subtlety of meaning in sight and sound and an increasing vividness of such experiences. Users also report enhanced sensations of touch, taste, and smell. An apparent slowing down of the time sense is universally reported. Recent findings continue to confirm earlier observations that acute marijuana intoxication causes a deterioration in intellectual and psychomotor performance, which is heavily dose-related and dependent on task complexity. The report also discusses acute physical toxicity, chronic physical effects, genetics and birth defects, psychiatric illness, therapeutic uses, and future research directions.