http://www.ukcia.org/research/gettman.htm

Addiction Potential


Unfortunately, fact and fancy have become irrationally mixed regarding marihuana's physiological and psychological properties. Marihuana clearly is not in the same chemical category as heroin insofar as its physiologic and psychological effects are concerned. In a word, cannabis does not lead to physical dependence. No torturous withdrawal syndrome follows the sudden cessation of chronic, heavy use of marihuana. Although evidence indicates that heavy, long-term cannabis users may develop psychological dependence, even then the level of psychological dependence is no different from the syndrome of anxiety and restlessness seen when an American stops smoking tobacco cigarettes.
-Commissioned by President Richard M. Nixon, March, 1972