Cannabis is nowhere near as addictive as nicotine or alcohol but it is wrong to say it is not habit-forming.

Many users compare their daily cannabis habit with dependency on caffeine. The UK Department of Health summed it up neatly: "Cannabis is a weakly addictive drug but does induce dependence in a significant minority of regular users."

Around 9% of users become addicted (1), although some studies estimate that over 50% of users have "impaired control" over their use of cannabis. Of the 70 million Americas estimated to have tried the drug, around two million use it daily. (2)

tolerance
Tolerance builds up rapidly after a few doses and disappears rapidly after a couple of days of abstinence. Heavy users need as much as eight times higher doses to achieve the same psychoactive effects as regular users using smaller amounts. They still get stoned but not as powerfully.

One effect of cannabis you can't develop tolerance to is "the stimulatory effect on the appetite" or munchies.

withdrawal
If you are a regular cannabis smoker (every day) and you stop smoking, you will experience some of the following withdrawal symptoms: restlessness, irritability, mild agitation, insomnia, nausea, sleep disturbance, sweats, and intense dreams. These symptoms however are mild and short-lived, lasting 2 to 4 days. (3)

1. MARIJUANA and MEDICINE: Assessing The Science Base, pg 95
2. Lynn Zimmer, co-author 'Marijuana Myths, Marijuana Facts', New Scientist online interview, 1998 3. MARIJUANA and MEDICINE: Assessing The Science Base, pg 90-91