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Published: 10 November 2010

Adverse health effects of cannabis use

Several recent reviews have looked into the adverse health effects associated with cannabis use (EMCDDA, 2008a; Hall and Degenhardt, 2009). These include acute effects such as anxiety, panic reaction and psychotic symptoms, which are often reported by first time users. Such effects account for a substantial number of drug-related hospital emergencies demands in the few countries that monitor them. Cannabis use also appears to increase the risk of being involved in a traffic accident by two to three times (EMCDDA, 2008b).

Cannabis use can also have chronic effects which may be directly linked with the patterns of use (frequency and quantities). These include cannabis dependence but also chronic bronchitis and other respiratory diseases. Cannabis use during pregnancy could reduce birth weight, but does not seem to cause birth defects. The association of cannabis use with depression and suicide is still uncertain.

The impact of cannabis on cognitive performance, and its reversibility, remains unclear. Regular cannabis use in adolescence might adversely affect mental health in young adults, with evidence of an increased risk of psychotic symptoms and disorders that increase with frequency of use (Hall and Degenhardt, 2009; Moore et al., 2007).

While the individual risk related to cannabis use seems lower than for heroin or cocaine, health problems do exist and, due to high prevalence of use, the impact of cannabis on public health may be significant. Particular attention should be given to cannabis use by adolescents and people with mental health problems. Frequent cannabis use, use over longer periods, when driving or during other potentially dangerous activities, are other matters of concern.

EMCDDA (2008a), A cannabis reader: global issues and local experiences, EMCDDA Monograph, Publications Office of the European Union, Luxembourg.

EMCDDA (2008b), Drug use, impaired driving and traffic accidents, EMCDDA Insights, Publications Office of the European Union, Luxembourg.

Hall, W. and Degenhardt, L. (2009), ‘Adverse health effects of non-medical cannabis use’, Lancet 374, pp. 1383–91.

Moore, T.H., Zammit, S., Lingford-Hughes, A., Barnes, T.R., Jones, P.B. et al. (2007), ‘Cannabis use and risk of psychotic or affective mental health outcomes: a systematic review’, Lancet 370, pp. 319–28.

About the EMCDDA

The European Monitoring Centre for Drugs and Drug Addiction (EMCDDA) is the reference point on drugs and drug addiction information in Europe. Inaugurated in Lisbon in 1995, it is one of the EU's decentralised agencies. Read more >>

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Page last updated: Monday, 18 October 2010