Documents the harm to young people from marijuana use. The Denver-area teenagers studied were in delinquency/substance abtise treatment and most were dependent on marijuana, although most reported behavior problems predated, and were not initially caused by, drug use. Most of the dependent youth had let marijuana control their lives, interfering with school, home, and work situations and with driving. Three-quarters of the dependent young people spent much time in getting, using or recovering from the effects of marijuana. Two-thirds had given up important activities to use or acquire marijuana. Most of these dependent children experienced withdrawal symptoms when they tried to quit marijuana. Among other findings of this study:

Marijuana is a strong reinforcer of itself, propelling further use.
Among the dependent youth, even moderate marijuana use commonly led to dependence. For those who had used marijuana at least 6 times, 83% developed dependence.
Progression in marijuana use was significantly more rapid than for alcohol.
An anti-drug prevention organization recently compiled an extensive bibliography of studies showing marijuana’s harm. This is available from DNE/Strategic Intelligence upon request.
Aside from the harm caused by marijuana directly, its role as a “gateway drug” has been well established. Marijuana use is of particular concern because, for some, it is a forerunner of use of other drugs with their attendant problems. Documentation of the association of marijuana with abuse of more serious drugs was reported in the June 1997 Bulletin. One study showed that the earlier a person starts using marijuana, the more likely it is that they will at least experiment with other drugs. This is shown in the graph below and suggests that the longer marijuana use can be prevented, the better the chance for a drug-free life.
Risk of using other drugs varies directly with how young a person is when they start using marijuana

Source:Recent research conducted at the University of Colorado and published in Drug and Alcohol Dependence
How Marijuana Use Relates to Other Drug Use
(Based on Federal Drug Use Figures)