Cannabis use significantly increases the risk of incidence and persistence of subclinical psychotic symptoms.
Summary
Prospective cohort study (n=1.923, adolescents and young adults, age 14-24 at baseline); cannabis use in adolescence increased the risk of later occurring psychotic symptoms (OR=1,9, 95% CI 1,1–3,1; p=0,021); persistent use doubled the risk of persistent subclinical psychotic symptoms (OR=2,2, 95% CI 1,2–4,2; p=0,016); incidence rate of psychotic symptoms 31% in adolescent users vs. 20% in non-users.
P
PopulationGeneral population, adolescents and young adults (14–24 years), n=1923, without psychotic symptoms and cannabis use at baseline
I
InterventionIncident or continued cannabis use (naturalistically assessed over 10 years, 3 measurement time points)
C
ControlNo cannabis use
O
OutcomeIncident cannabis use increases risk of later psychotic symptoms (adj. OR 1,9; 95%-CI 1,1–3,1; p=0,021); continued use increases risk of persistent psychotic symptoms (adj. OR 2,2; 95%-CI 1,2–4,2; p=0,016)
Confidence in the evidence
Very lowLowModerateHigh
Low
The second of four GRADE levels, the effect estimate is of limited reliability.
Quality profile
Sample size★★★★★
Blinding—
Effect sizeClear benefit
Citations / year★★★★★
Authors
Kuepper R, van Os J, Lieb R, Wittchen HU, Höfler M, Henquet C.
<h4>Objective</h4>To determine whether use of cannabis in adolescence increases the risk for psychotic outcomes by affecting the incidence and persistence of subclinical expression of psychosis in the general population (that is, expression of psychosis below the level required for a clinical diagnosis).<h4>Design</h4>Analysis of data from a prospective population based cohort study in Germany (early developmental stages of psychopathology study).<h4>Setting</h4>Population based cohort study in Germany.<h4>Participants</h4>1923 individuals from the general population, aged 14-24 at baseline.<h4>Main outcome measure</h4>Incidence and persistence of subthreshold psychotic symptoms after use of cannabis in adolescence. Cannabis use and psychotic symptoms were assessed at three time points (baseline, T2 (3.5 years), T3 (8.4 years)) over a 10 year follow-up period with the Munich version of the composite international diagnostic interview (M-CIDI).<h4>Results</h4>In individuals who had no reported lifetime psychotic symptoms and no reported lifetime cannabis use at baseline, incident cannabis use over the period from baseline to T2 increased the risk of later incident psychotic symptoms over the period from T2 to T3 (adjusted odds ratio 1.9, 95% confidence interval 1.1 to 3.1; P=0.021). Furthermore, continued use of cannabis increased the risk of persistent psychotic symptoms over the period from T2 to T3 (2.2, 1.2 to 4.2; P=0.016). The incidence rate of psychotic symptoms over the period from baseline to T2 was 31% (152) in exposed individuals versus 20% (284) in non-exposed individuals; over the period from T2 to T3 these rates were 14% (108) and 8% (49), respectively.<h4>Conclusion</h4>Cannabis use is a risk factor for the development of incident psychotic symptoms. Continued cannabis use might increase the risk for psychotic disorder by impacting on the persistence of symptoms.