Marihuana in man: three years later.

The past 3 years of renewed research on the effects of marihuana in man has added little not previously known about the clinical syndromes produced by the drug. The major advance has been a quantification of dose in relation to clinical phenomena, and a beginning of an understanding of the drug's metabolism. The crucial clinical experiments in regard to the social questions about marihuana, such as the possible deleterious effects from chronic use, cannot be answered by laboratory experiments. These must be settled by close observations made on those who experiment on themselves. It should be possible, within a relatively short time, to determine whether marihuana has any medical utility, but the future would appear to be no more promising than the past in this regard. The mechanisms by which marihuana alters mental functions are not likely to be answered in man, nor even answered soon by animal studies. As marihuana may be unique among drugs in that more experimentation has been accomplished in man than in animals, it may be necessary to look to additional animal studies to provide leads for pertinent future studies in man.