1 / 24

IS CANNABIS A RISK FACTOR FOR SCHIZOPHRENIA?

IS CANNABIS A RISK FACTOR FOR SCHIZOPHRENIA?. Jouko Miettunen Department of Public Health and Primary Care Institute of Public Health University of Cambridge. February 3, 2003. CONTENTS OF THE PRESENTATION. cannabis and cannabis use schizophrenia association and causality

toya
Download Presentation

IS CANNABIS A RISK FACTOR FOR SCHIZOPHRENIA?

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. IS CANNABIS A RISK FACTOR FOR SCHIZOPHRENIA? Jouko Miettunen Department of Public Health and Primary Care Institute of Public Health University of Cambridge February 3, 2003

  2. CONTENTS OF THE PRESENTATION • cannabis and cannabis use • schizophrenia • association and causality • summaries and limitations of the studies • conclusions

  3. SOURCE OF CANNABIS • hemp plant, Cannabis sativa • contain cannabinoids • major active component • 9-tetrahydrocannabinol • preparations of cannabis • illicit drugs • marijuana (leaves, stalks, flowers, seeds) • hashish (resin) • also legal drugs • conflicting attitudes among researchers

  4. CANNABIS USE • measured by questionnaires and urine/hair test • known effects • 10% become dependent and gateway to other drugs • depression and anxiety • somatic disorders (e.g. cancer) • impair cognitive and driving skills • brain effects (releases dopamine) • use as a therapeutic drug • multiple sclerosis, epilepsy, cancer, AIDS, etc. • BMA (1997): “Therapeutic Uses of Cannabis”

  5. PREVALENCE OF CANNABIS USE Annual prevalence estimates of cannabis use in the late 1990s (“official statistics” i.e. various questionnaires, surveys and estimates) 3.5% TOTAL 4.9% EUROPE 9.4% United Kingdom 4.1% Netherlands 6.6% NORTH AMERICA 8.3% United States 4.7% SOUTH AMERICA 1.6% ASIA 0.5% China 3.2% India 8.1% AFRICA 18.8% OCEANIA 0 5 10 15 20 % of population age 15 and above United Nations Office on Drugs and Crime

  6. CANNABIS USE BY AGE current monthly use (survey in New York, N=1,160) Chen et al. 1995 • use among UK students (Webb et al. 1996) • any use 60% and regular use 20% • use is increasing in most countries • especially among people under age 16 • in some parts of the world more common than alcohol use

  7. SCHIZOPHRENIA • chronic, severe, and disabling mental disease • diagnosed using structured interviews (ICD-10: F20) • life-time prevalence approximately 1% • not increasing in general, though e.g. in south London • prevalence of some psychotic symptoms in general population (Eaton et al. 1991): • paranoid symptoms 10% • hallucinations 5-8% • bizarre delusions 2%

  8. AGE AT ONSET OF SCHIZOPHRENIA 30 Female Male 20 10 0 12-14 15-19 20-24 25-29 30-34 35-39 40-44 45-49 50-54 55-59 patients (%) years age group Häfner et al. 1993

  9. PREVALENCE OF CANNABIS USE AMONG PSYCHOTIC PATIENTS • difficult to compare due to the selection of cases (inpatients/outpatients) and controls • most case-control studies report that cannabis use is about 2 times more common among psychotic patients than among general population based controls • among schizophrenia patients • prevalence estimates vary between samples from 5 to 50 % • 4 times more often any drugs (UK study, McCreadie 2002)

  10. CANNABIS USERS AMONG SCHIZOPHRENIA PATIENTS • younger age at onset and more males • more unemployment and alcoholism • worse course of schizophrenia • more positive symptoms • poorer compliance with treatment • more frequent hospitalisation (unclear?) • less negative symptoms in short-term (unclear?) • more patients with catatonic subtype of schizophrenia (Hambrecht and Häfner 2000)

  11. EFFECTS OF CANNABIS USE ON VULNERABLE CASES • cannabis use is a risk for psychotic diagnosis in subjects who have already have symptoms (van Os et al. 2002) • patients with cannabis associated psychosis have increased familial risk for schizophrenia (McGuire et al. 1995) • some recent high-risk studies (Phillips et al. 2002, Miller et al. 2001)

  12. CANNABIS USERS IN GENERAL POPULATION • have more psychotic symptoms than non-users at age 18-20 (Fergusson et al. 2003) • adjusted OR 1.8 (95% CI: 1.2-2.6) • have more often schizotypal personality traits (Williams et al. 1996, Dumas et al. 2002)

  13. POTENTIAL CONFOUNDERS • age and sex • urban birth, social class and marital status • alcohol use, smoking and use of other drugs • stressful life-events • migrant/minority status (e.g. Afro-Caribbeans in UK) • premorbid symptoms (e.g. social adjustment difficulties) • personality traits and IQ • familial risk of schizophrenia and/or cannabis use

  14. CAUSALITY BETWEEN CANNABIS USE AND SCHIZOPHRENIA • generally accepted that cannabis intoxication can cause brief psychotic episodes • can cannabis use cause schizophrenia? • or can the direction of causality be reversed?

  15. PROBLEMS WITH CHRONOLOGY What is the temporal order? CANNABIS USE first use regular use heavy use AGE premorbid symptoms psychotic symptoms diagnosis SCHIZOPHRENIA

  16. PROBLEMS WITH POOLING THE STUDIES Various exposure and outcome combinations in the studies: CANNABIS USE SCHIZOPHRENIA • any use • regular use • heavy use • times in a life-time • times in a year/month/… • current use • cannabis abuse/dependence • etc. • any psychotic symptoms • symptoms in a year/month • pathological level of symptoms • need for care due to symptoms • any psychotic diagnosis • schizophreniform disorder • schizophrenia • etc.

  17. SCHIZOPHRENIA AS AN OUTCOME Swedish conscript study (1) • cohort of 18-20 year old males (N=50,045) • questionnaires at conscription 1969/70 • hospital register follow-up until 1995 • ICD-8/9 schizophrenia diagnosis • Andréasson et al. 1987 • Andréasson et al. 1989 • Zammit et al. 2002

  18. Swedish conscript study (2) risk for schizophrenia: • ever used cannabis • adjusted OR 1.9 (95% CI: 1.1.-3.1) • used cannabis more than 50 times • adjusted OR 6.7 (95% CI: 2.1.-21.7) • significant linear trend for frequency of use • cannabis use was not associated with other psychoses than schizophrenia

  19. Swedish conscript study (3) limitations: • no information on possible confounding factors in the follow-up period • no information on familial risk for schizophrenia • validity of the exposure (underreporting?) • validity of the outcome (underreporting?) • not many cannabis users got schizophrenia • 1.4% if ever used • 3.8% if used >50 times • 0.6% in controls

  20. SYMPTOMS AS AN OUTCOME Netherlands 1996-99 • population based survey (N=4,045; 18-64 years) • any cannabis use predicted the presence of psychotic symptoms at 3-year follow-up • any symptoms: adjusted OR = 2.8 (95% CI: 1.2-6.5) • pathology level of symptoms: adj. OR = 24.2 (5.4-107.5) • statistically significant trend for dose-response • cannabis use was a risk for psychotic diagnosis in subjects who already have psychotic symptoms • limitations: no information on familial risk for schizophrenia, short follow-up and 43% drop-outs van Os et al. 2002

  21. New Zealand 1983-99 • general population birth cohort 1972-73 (N=759) • cannabis use ≥3 times prior to age 15 predicted • schizophrenia symptoms at 26 • adjusted OR = 6.6 (4.8-8.3) • and schizophreniform disorder at age 26 • adjusted OR = 3.1 (0.7-13.3) (non-significant) • use of other drugs was not associated with outcome • strength: psychiatric symptoms at age 11 • limitations: no information on familial risk for schizophrenia and did not use schizophrenia as an outcome Arseneault et al. 2002

  22. LIMITATIONS OF THE STUDIES • misclassification bias • lack of confirmation of the biological presence of cannabis in the organism • reliability of psychiatric diagnoses may be worse in subjects with comorbid cannabis use • not always adjusted for all potential confounders • short follow-up times • attitude of the researchers • difficult to interpret results and conclusions

  23. PROBLEMS WITH CHRONOLOGY Schizophrenia patients using cannabis can be defined into groups chronologically CANNABIS USE AGE self-medicating patients • vulnerable patients • or • increased dopamine level • increases positive symptoms of schizophrenia • similar risk factors for cannabis use and schizophrenia • or • cannabis is the trigger SYMPTOMS OF SCHIZOPHRENIA all the groups include also people who have schizophrenia independently on cannabis use, and vice versa!

  24. CONCLUSIONS • use of cannabis can cause psychotic symptoms and even schizophrenia especially in some vulnerable cases • BUT: • would schizophrenia have occurred in these individuals in any case (cannabis use only precipitates schizophrenia)? • does not count for many schizophrenia cases? • IN FUTURE: • large prospective studies with long follow-up time, schizophrenia diagnosis as an outcome and comprehensive information on confounding variables • case-control study starts in South London 2003

More Related