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Psychopathological effects of cannabis use: a critical analysis of the scientific data and methodologies

Research project DR/06 (Research action DR)

Persons :

Description :

Cannabis is probably the most frequently used illicit drug in the western world. In Europe it is estimated that 10 to 35 % of adolescents and about 20 % of the adult population ever used cannabis. In the U.S., Australia and New Zealand the prevalences are even higher. The risk that cannabis will be used for a certain period is important: the continuation rate in the EU lies between 24 and 38 % while in Australia it nearly amounts up to 50 %. 10 % of all ever users of cannabis met the DSM IV criteria for cannabis dependence and especially adolescents and young adults are a risk (Cannabis Report, Ministery of Public Health of Belgium, 2002*).

Several studies evaluated the effects of chronic cannabis use concerning somatic and mental health, less studies evaluated psychosocial aspects. People with a predisposition for or suffering of psychiatric disorders are especially vulnerable for the negative effects and to develop dependency of cannabis and for the negative impact on the prognosis of the psychiatric disorder. Nevertheless the results of the different studies are insufficient to offer the responsibles a firm bases to found their attitudes and to define the strategies and policy towards cannabis use. Largely this is due to methodological differences, deficits and incompleteness of different studies and as such the importance and the clarity of the obtained results is obscured.

It is indicated to study the consequences on mental health of medium (2 to 5 years) and long term (5 to 10 years and more than 10 years) cannabis use and also to recognize the different methodological deficits that impede the interpretation of the essential information. A critical analysis of the results and of the methodology reported in the literature since 1985 will allow to gather the information useful and necessary to indicate lines of research and appropriate methods to evaluate the effects of medium and long term cannabis use.
The data in the scientific literature since 1985 will be reviewed by a literature search using different keywords** (Medline, PsychLib...) and a review of the relevant studies will be established.

A first qualitative analysis will offer insight in the different problems and research lines concerning the effects and problems of cannabis use more specifically concerning its impact on mental health.

The studies will be analysed concerning psychiatric disorders (affective disorders, psychotic disorders, risk of abuse and dependency) and the impact of cannabis use on incidence, duration, prognosis. The results will be analysed and evaluated.

The different research methods in each area (evaluation of substance use and health risks, statistical methodology) will be examinated and evaluated.

The conclusion based on the evaluation and the critical analysis of the reviewed study results and of the research methods will allow to indicate the shortcomings and open questions concerning the effects of medium and long term cannabis use on en mental health and to suggest important lines of research and adequate research methods.

* Cannabis 2002 Report, Ministery of Public Health of Belgium. A joint international effort at the initative of of the Ministers of Public Health of Belgium, France, Germany, The Netherlands, Switzerland. Technical Report of the International Scientific Conference Brussels, Belgium, 25/02/2002.

** General keywords give acces to all articles THC/cannabis/marihuana; strings of words that give acces to articles that were not selected by the general keywords and give an idea about the importance of data (number of articles) in each area: cannabis/THC/marihuana en mental health, psychology/psychiatry/ neuropsychology, pharmacology/tolerance/withdrawal/dependency.

Documentation :

Psychiatrische effecten van cannabisgebruik: een kritische analyse van wetenschappelijke resultaten en onderzoeksmethoden : eindrapport    Brussel : Federaal wetenschapsbeleid, 2003 (SP1232)
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Effets psychiatriques de l'usage de cannabis : analyse critique de résultats scientifiques et de méthodes d'investigation : résumé    Bruxelles : Politique scientifique fédérale, 2003 (SP1256)
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Psychiatrische effecten van cannabisgebruik: Een kritische analyse van wetenschappelijke resultaten en onderzoeksmethoden : samenvatting    Brussel : Federaal Wetenschapsbeleid, 2003 (SP1257)
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Psychiatric effects of cannabis use: A critical analysis of scientific results and research methods : summary    Brussels : Science Policy Office, 2003 (SP1258)
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