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Media Campaign Fact Sheets
Marijuana and Mental Health
Youth marijuana use is risky and can lead to serious consequences, including mental health problems. Researchers have long known that marijuana use has been associated with psychopathology. In the past decade, research on the psychiatric implications of the drug has increased dramatically. In the past three years, in particular, evidence has been accumulating that regular marijuana use can not only aggravate already existing mental illness, but that it may precede, or act as a catalyst, in mental health problems, including depression, suicidal thoughts and schizophrenia. This new research also identifies two crucial risk factors:
The age when marijuana is first smoked has a major impact on the later development of mental health problems. The earlier the use, the greater the implications.
There is an increased risk of depression, suicidal thoughts and schizophrenia as a result of marijuana use, even among people with no prior history of a disorder. However, those with a predisposition for mental illness are particularly vulnerable. In the case of psychotic disorders, this is estimated to be about one in four people.
Depression and Suicidal Thoughts
Several recent studies have linked youth marijuana use with increases in depression and suicidal thinking.
Teens age 12 to 17 who smoke marijuana weekly are three times more likely than non-users to have thoughts about committing suicide.1
Some research shows that marijuana use can precede symptoms of depression. Girls (ages 14–15) who used marijuana daily were five times more likely to face depression at age 21. Weekly use among all teens studied doubled the risk for depression.2
A study of adults found that marijuana use quadrupled the risk of later major depression.3
A study of 1,265 children over a 21-year period found that marijuana use, particularly heavy or regular use, was associated with later increases in depression, suicidal thoughts and suicide attempts.4
Past-year marijuana use has been linked to social withdrawal, anxiety, depression, attention problems and thoughts of suicide in adolescents.5
Research with twins found that the twin who was dependent on marijuana was almost three times more likely to think about suicide and attempt suicide than his/her non-marijuana dependent co-twin.6
Schizophrenia
Marijuana use has been linked to early-onset schizophrenia, and several recent studies show that marijuana use during adolescence increases the risk of psychotic disorders in adulthood.7
Heavy marijuana users are almost seven times more likely than non-users to be diagnosed with schizophrenia later in life.8
Among men suffering from schizophrenia, those who had used marijuana were much more likely to experience their first psychotic episode at an early age.9
A recent study found that that the earlier the use of marijuana (age 15 vs. age 18), the greater the risk of schizophrenia.10
A study published in 2005 found that regular use of marijuana may double the risk of developing psychotic disorders and that marijuana causes chemical changes to the brain. The study maintains that smoking marijuana causes symptoms even when other factors are taken into consideration.11
Genetic Predisposition
Recent evidence suggests that some people's genetic make-up may predispose them to be particularly vulnerable to the effects of marijuana on mental health.
An analysis of 2,437 young people found that marijuana use moderately increases the risk of psychopathology. The risk for those with a predisposition for psychopathology was much higher.12
A study published in spring 2005 found that as many as one in four people may have a genetic profile that makes marijuana five times more likely to trigger psychotic disorders.13
Parents Can Make a Difference
Parents can make a difference by talking to their teens about the risks of marijuana and by monitoring their behavior. They can also take early action if they see signs of drug use or emotional problems.14
Parents are the most powerful influence on their kids when it comes to drugs. A report from the National Household Survey on Drug Abuse showed that the rate of past-month marijuana use was lower among kids who believed their parents would disapprove.
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References
1 Greenblatt, J. Adolescent self-reported behaviors and their association with marijuana use. SAMHSA, 1998.
2 Patton, GC et al. Cannabis use and mental health in young people: cohort study. British Medical Journal, 325:1195–1198, 2002.
3 Bovasso, GB. Cannabis abuse as a risk factor for depressive symptoms. The American Journal of Psychiatry, 158:2033–2037, 2001.
4 Fergusson, DM et al. Cannabis use and psychosocial adjustment in adolescence and young adulthood. Addiction, 97:1123–1135, 2002.
5 Brook, JS et al. The effect of early marijuana use on later anxiety and depressive symptoms. NYS Psychologist, 35–40, 2001.
6 Lynskey, M et al. Major depressive disorder, suicidal ideation, and suicide attempt in twins discordant for cannabis dependence and early-onset cannabis use. Archives of General Psychiatry, 61:1026–1032, 2004.
7 Andreasson, S et al. Cannabis and schizophrenia: A longitudinal study of Swedish conscripts. Lancet, 26:1483–1486, 1987. Fergusson, DM et al. Cannabis dependence and psychotic symptoms in young people. Psychological Medicine, 33:15–21, 2003. van Os, J et al. Cannabis use and psychosis: a longitudinal population-based study. American Journal of Epidemiology, 156:319–327, 2002.
8 Zammit, S et al. Self-reported cannabis use as a risk factor for schizophrenia in Swedish conscripts of 1969: historical cohort study. British Medical Journal, 325:1199–1201, 2002.
9 Veen, N et al. Cannabis use and age at onset of schizophrenia. The American Journal of Psychiatry, 161:501-506, 2004.
10 Arseneault L, et al. Cannabis use in adolescence and risk for adult psychosis: longitudinal prospective study. British Medical Journal, 325:1212–1213, 2002.
11 Fergusson, DM et al. Tests of causal linkages between cannabis use and psychotic symptoms. Addiction, 100, 3:354–366, 2005.
12 van Os, J et al. Prospective cohort study of cannabis use, predisposition for psychosis, and psychotic symptoms in young people. British Medical Journal, 330:11–, 2005.
13 Caspi A, et al. Moderation of the effect of adolescent-onset cannabis use on adult psychosis by a functional polymorphism in the catechol-o-methyltransferase gene: Longitudinal evidence of a gene X environment interaction. Biological Psychiatry (Article in press).
14 The National Household Survey on Drug Abuse (NHSDA) Report: Parental disapproval of youths' substance abuse. Department of Health and Human Services, Substance Abuse and Mental Health Services Administration, 2002.
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Last Updated: May 3, 2005
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