It is estimated that 2.7 million Americans are dependent on marijuana.
A Pew Charitable Trust investigation found that marijuana addiction does exist and is growing. While hard numbers are hard to come by, data suggests about 9% of all users become addicted to marijuana (17% among those who start as adolescents). Some treatment centers report increases in those requesting help which may be due to higher concentrations of THC levels. Selective breeding has increased the potency today to 20-30%, up from 2-4% of several decades ago.
PositiveTip: The best policy is to never start, but if you are dependent, get qualified help immediately.