• cannabis;
  • adolescence;
  • psychotic disorders;
  • age of onset

Objective:  Cannabis use increases the risk for psychosis, but psychotogenic effects of cannabis may be restricted to exposure during early adolescence.

Method:  Four hundred and seventy-two participants (aged 12–23 years), randomly selected from the general population in Trinidad, completed questionnaires on past and current cannabis use and psychotic symptoms (using the Community Assessment of Psychic Experiences).

Results:  Cannabis use increased the risk of experiencing psychotic symptoms and this effect was conditional on early exposure, defined around the mean age of onset of cannabis use. Thus, exposure before but not after the age of 14 years predicted psychotic symptoms (respectively β: 0.71, 95% CI 0.22; 1.19, P = 0.004 and β: −0.11, 95% CI −0.57; 0.36, P = 0.66). The developmental effect of cannabis use was independent of use of other drugs or current use of cannabis.

Conclusion:  Early adolescence may be a critical period with regard to the psychotogenic effect of cannabis across geographical settings and ethnic groups.