Caution: Marijuana may not be lesser evil / USA Today, 5 February 2007
http://www.usatoday.com/news/health/2007-02-05-marijuana_x.htm
Rita Rubin
"... But studies have shown that when regular pot smokers quit, they do experience withdrawal symptoms, a characteristic used to predict addictiveness. Most users of more addictive drugs, such as cocaine or heroin, started with marijuana, scientists say, and the earlier they started, the greater their risk of becoming addicted. ... "Is marijuana a gateway drug? That question has been debated since the time I was in college in the 1960s and is still being debated today," ... "That's because it's impossible to separate marijuana from the environment in which it is smoked, short of randomly assigning people to either smoke pot or abstain — a trial that would be grossly unethical to conduct."