Long-term marijuana use can lead to addiction; that is, people have difficulty controlling their drug use and cannot stop even though it interferes with many aspects of their lives. It is estimated that 9 percent of people who use marijuana will become dependent on it.10 The number goes up to about 1 in 6 in those who start using young (in their teens) and to 25-50 percent among daily users.11, 12 Moreover, a study of over 300 fraternal and identical twin pairs found that the twin who had used marijuana before the age of 17 had elevated rates of other drug use and drug problems later on, compared with their twin who did not use before age 17.13
According to the 2010 NSDUH, marijuana accounted for 4.5 million of the estimated 7.1 million Americans dependent on or abusing illicit drugs.1 In 2009, approximately 18 percent of people aged 12 and older entering drug abuse treatment programs reported marijuana as their primary drug of abuse.14
Marijuana addiction is also linked to a withdrawal syndrome similar to that of nicotine withdrawal, which can make it hard to quit. People trying to quit report irritability, sleeping difficulties, craving, and anxiety. They also show increased aggression on psychological tests, peaking approximately 1 week after they last used the drug.
10Anthony, J.; Warner, L.A.; and Kessler, R.C. Comparative epidemiology of dependence on tobacco, alcohol, controlled substances, and inhalants: Basic findings from the National Comorbidity Survey. Exp Clin Psychopharmacol 2:244-268, 1994.
11Hall, W.; and Degendardt, L. Adverse health effects of non-medical cannabis use. Lancet 374: 1383-1391, 2009.
12Hall, W. The adverse health effects of cannabis use: What are they, and what are their implications for policy? Int J of Drug Policy 20:458-466, 2009.
13Lynskey, M.T.; Heath, A.C.; Bucholz, K.K.; Slutske, W.S.; Madden, P.A.; Nelson, E.C.; Statham, D.J.; and Martin, N.G. Escalation of drug use in early-onset cannabis users vs. co-twin controls. JAMA 289(4): 427-433, 2003.
14Substance Abuse and Mental Health Services Administration. Office of Applied Studies. Treatment Episode Data Set (TEDS) Highlights-2009: National Admissions to Substance Abuse Treatment Services. Office of Applied Studies, DASIS Series: S-45, HHS Pub. No. (SMA) 09-4360, Rockville, MD: SAMHSA, 2008.