DEPRESSION AND SUICIDE
Beautrais, AL et al. Cannabis use and serious suicide attempts. Addiction, 94:1155-1164, 1999.
This study examined the relationship between cannabis abuse/dependence and risk of medically serious suicide attempts among 302 individuals attempting suicide and 1,028 random controls and found that marijuana use may be connected to the risk of a serious suicide attempt.
Brook, DW et al. Drug use and the risk of major depressive disorder, alcohol dependence, and substance use disorders. Archives of General Psychiatry, 59:1039-1044, 2002.
This longitudinal research of comorbid disorders found that early marijuana use during childhood and adolescence increased the risk of major depression by 17 percent. This study called attention to the importance of the psychiatric implications of early drug use.
Fergusson, DM et al. Cannabis use and psychosocial adjustment in adolescence and young adulthood. Addiction, 97:1123-1135, 2002.
This study of 1,265 New Zealand 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.
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.
This study looked at 600 same-sex twins, one of whom was dependent upon marijuana and one of whom was not. It 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. Additionally, cannabis dependence was associated with higher risk of major depressive disorder in fraternal but not in identical twins.
Patton, GC et al. Cannabis use and mental health in young people: cohort study. British Medical Journal, 325:1195-1198, 2002.
In this study, daily use of marijuana among girls increased the risk of depression five times. Weekly or more frequent marijuana use in teenagers doubled the risk of depression and anxiety.
Ramstrom, J. Adverse Health Consequences of Cannabis Use: A survey of scientific studies published up to and including the autumn of 2003. National Institute of Public Health, Sweden, 2004.
This is an extensive literature review of studies conducted worldwide on the detrimental effects of marijuana. It is an update of a review initially published in 1996 and covers studies through the fall of 2003. It finds a link between marijuana and depression and suicidal tendencies. The author points out that there is a growing body of evidence to support the claim that cannabis can provoke schizophrenia.
SCHIZOPHRENIA
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.
This report, a re-analysis of the Andreasson research (above), found that heavy marijuana users were
6.7 times more likely than non-users to be diagnosed with schizophrenia later in life. This was true for those who used marijuana only, as opposed to other drugs. The authors concluded that the findings are consistent with a causal relationship between cannabis use and schizophrenia and that self-medication with cannabis was an unlikely explanation for the association observed.
Arseneault L, et al. Cannabis use in adolescence and risk for adult psychosis: longitudinal prospective study. British Medical Journal, 325:1212-1213, 2002.
This longitudinal study agreed with the Andreasson results (above) and added new evidence: there is an increased risk of developing schizophrenia as a result of marijuana use, even among people with no prior history of a disorder, and that the earlier the use of marijuana (age 15 vs. age 18), the greater the risk of schizophrenia.
Arsenault L, et al. Causal association between cannabis and psychosis: examination of the evidence. British Journal of Psychiatry, 184:110-117, 2004.
This review of five studies from the United States, Europe and Australia found that all available population-based studies have concluded that cannabis use is associated with later schizophrenia outcomes and that cannabis use is a component cause of a variety of factors that lead to onset of schizophrenia.
Dean, B et al. Studies on [3H]CP-55940 binding in the human central nervous system: regional specific changes in density of cannabinoid-1 receptors associated with schizophrenia and cannabis use. Neuroscience, 103:9-15, 2001.
This study presented the first direct evidence that people with a predisposition for schizophrenia or other mental disorders are particularly vulnerable to the negative effects of marijuana on mental health. It showed that marijuana affects parts of the brain that are very closely related to those that may be responsible for schizophrenia.
Drewe, M et al. Cannabis and risk of psychosis. Swiss Medical Weekly, 134:659-663, 2004.
This literature review concludes that marijuana use is connected with schizophrenia and depression and drew the following conclusions: Cannabis consumption affects dopamine concentrations in the brain and can induce or modulate the development of psychotic symptoms, including schizophrenia, and that young age of cannabis use is an additional risk factor for psychosis. Cannabis consumption can also lead to other psychiatric disorders, including depression and cognitive disturbances.
Stefanis, NC et al. Early adolescent cannabis exposure and positive and negative dimensions of psychosis. Addiction, 99:1333-1341, 2004.
This study of 3,500 19-year-olds in Greece found that marijuana use, especially at a young age, contributes to psychotic symptoms. It reports that there are very high risks in individuals using in early adolescence, particularly below age 16.
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.
This analysis of 2,437 young people found that marijuana use moderately increases the risk of psychotic symptoms. The risk for those with a predisposition for psychosis was much higher.
van Os, J et al. Cannabis use and psychosis: a longitudinal population-based study. American Journal of Epidemiology, 156:319-327, 2002.
The research confirms previous suggestions that cannabis use increases the risk of psychotic disorders in people without a predisposition, and a poor prognosis for those with an established vulnerability.
Veen, N et al. Cannabis use and age at onset of schizophrenia. The American Journal of Psychiatry, 161:501-506, 2004.
This study found that men with a history of marijuana use experienced their first psychotic episode at a significantly younger age than those with no such history.
Verdoux, H et al. Effects of cannabis and psychosis vulnerability in daily life: an experience sampling test study. Psychological Medicine, 33:23-32, 2003.
This study of undergraduate students in France refutes the idea that people with psychotic symptoms self-medicate with marijuana. It found that people who are vulnerable to psychosis are more susceptible to the detrimental effects of marijuana than those without a predisposition. The authors conclude, The public health impact of the widespread use of cannabis may be considerable.
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