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If cannabis caused schizophrenia--how many cannabis users may need to be prevented in order to prevent one case of schizophrenia? England and Wales calculations.

Abstract

BACKGROUND

We consider how many cannabis users may need to be prevented in order to prevent one case of schizophrenia or psychosis [defined as number needed to prevent (NNP)].

METHOD

Calculation for England and Wales using best available estimates of: incidence of schizophrenia; rates of heavy and light cannabis use; and risk that cannabis causes schizophrenia.

RESULTS

In men the annual mean NNP for heavy cannabis and schizophrenia ranged from 2800 [90% confidence interval (CI) 2018-4530] in those aged 20-24 years to 4700 (90% CI 3114-8416) in those aged 35-39. In women, mean NNP for heavy cannabis use and schizophrenia ranged from 5470 (90% CI 3640-9839) in those aged 25-29 to 10 870 (90% CI 6786-22 732) in 35-39-year-olds. Equivalent mean NNP for heavy cannabis use and psychosis were lower, from 1360 (90% CI 1007-2124) in men aged 20-24 and 2480 (90% CI 1408-3518) in women aged 16-19. The mean and median number of light cannabis users that would need to be prevented in order to prevent one case of schizophrenia or psychosis per year are four to five times greater than among heavy users.

CONCLUSIONS

The number of young people who need to be exposed to an intervention to generate NNP and prevent one case of schizophrenia will be even larger. The public health importance of preventing cannabis to reduce schizophrenia or psychosis remains uncertain. More attention should be given to testing the hypothesis that cannabis is related causally to psychotic outcomes, and to considering what strategies will be the most effective in reducing heavy cannabis use among young people.

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  • Authors+Show Affiliations

    ,

    Social Medicine, University of Bristol, Canynge Hall, Bristol BS8 2PR, UK. matthew.hickman@bristol.ac.uk

    , , , , ,

    Source

    Addiction (Abingdon, England) 104:11 2009 Nov pg 1856-61

    MeSH

    Adolescent
    Adult
    Epidemiologic Methods
    Female
    Humans
    Male
    Marijuana Abuse
    Psychoses, Substance-Induced
    Research Design
    Schizophrenia
    Sex Factors
    United Kingdom
    Young Adult

    Pub Type(s)

    Journal Article

    Language

    eng

    PubMed ID

    19832786

    Citation

    Hickman, Matt, et al. "If Cannabis Caused Schizophrenia--how Many Cannabis Users May Need to Be Prevented in Order to Prevent One Case of Schizophrenia? England and Wales Calculations." Addiction (Abingdon, England), vol. 104, no. 11, 2009, pp. 1856-61.
    Hickman M, Vickerman P, Macleod J, et al. If cannabis caused schizophrenia--how many cannabis users may need to be prevented in order to prevent one case of schizophrenia? England and Wales calculations. Addiction. 2009;104(11):1856-61.
    Hickman, M., Vickerman, P., Macleod, J., Lewis, G., Zammit, S., Kirkbride, J., & Jones, P. (2009). If cannabis caused schizophrenia--how many cannabis users may need to be prevented in order to prevent one case of schizophrenia? England and Wales calculations. Addiction (Abingdon, England), 104(11), pp. 1856-61. doi:10.1111/j.1360-0443.2009.02736.x.
    Hickman M, et al. If Cannabis Caused Schizophrenia--how Many Cannabis Users May Need to Be Prevented in Order to Prevent One Case of Schizophrenia? England and Wales Calculations. Addiction. 2009;104(11):1856-61. PubMed PMID: 19832786.
    * Article titles in AMA citation format should be in sentence-case
    TY - JOUR T1 - If cannabis caused schizophrenia--how many cannabis users may need to be prevented in order to prevent one case of schizophrenia? England and Wales calculations. AU - Hickman,Matt, AU - Vickerman,Peter, AU - Macleod,John, AU - Lewis,Glyn, AU - Zammit,Stan, AU - Kirkbride,James, AU - Jones,Peter, PY - 2009/10/17/entrez PY - 2009/10/17/pubmed PY - 2010/3/18/medline SP - 1856 EP - 61 JF - Addiction (Abingdon, England) JO - Addiction VL - 104 IS - 11 N2 - BACKGROUND: We consider how many cannabis users may need to be prevented in order to prevent one case of schizophrenia or psychosis [defined as number needed to prevent (NNP)]. METHOD: Calculation for England and Wales using best available estimates of: incidence of schizophrenia; rates of heavy and light cannabis use; and risk that cannabis causes schizophrenia. RESULTS: In men the annual mean NNP for heavy cannabis and schizophrenia ranged from 2800 [90% confidence interval (CI) 2018-4530] in those aged 20-24 years to 4700 (90% CI 3114-8416) in those aged 35-39. In women, mean NNP for heavy cannabis use and schizophrenia ranged from 5470 (90% CI 3640-9839) in those aged 25-29 to 10 870 (90% CI 6786-22 732) in 35-39-year-olds. Equivalent mean NNP for heavy cannabis use and psychosis were lower, from 1360 (90% CI 1007-2124) in men aged 20-24 and 2480 (90% CI 1408-3518) in women aged 16-19. The mean and median number of light cannabis users that would need to be prevented in order to prevent one case of schizophrenia or psychosis per year are four to five times greater than among heavy users. CONCLUSIONS: The number of young people who need to be exposed to an intervention to generate NNP and prevent one case of schizophrenia will be even larger. The public health importance of preventing cannabis to reduce schizophrenia or psychosis remains uncertain. More attention should be given to testing the hypothesis that cannabis is related causally to psychotic outcomes, and to considering what strategies will be the most effective in reducing heavy cannabis use among young people. SN - 1360-0443 UR - https://www.unboundmedicine.com/medline/citation/19832786/full_citation/If_cannabis_caused_schizophrenia_how_many_cannabis_users_may_need_to_be_prevented_in_order_to_prevent_one_case_of_schizophrenia_England_and_Wales_calculations_ L2 - https://doi.org/10.1111/j.1360-0443.2009.02736.x DB - PRIME DP - Unbound Medicine ER -