Data were used from 50,718 respondents in 17 countries, both developed and developing, that participate in the WHO World Mental Health Surveys. This is a global mental health-epidemiological study conducted in the general population of the countries, including the Netherlands.
The same instrument was used in all the countries to determine the age of onset of cannabis use, the prevalence of mental health disorders and the age at which these arose. In the Netherlands, the project was headed by the Trimbos Institute and the University of Groningen.
For all the countries together, the association between early cannabis use and the later onset of depression was limited but significant. The chance of later developing depressive symptoms was 1.5 times higher among those who had used cannabis before the age of 17, compared to those who used cannabis only after this age or not at all.
No difference was found between female respondents (1.6 times more likely) and males (1.4 times more likely). Differences were found however between countries: South Africa (3.9 more likely) and Nigeria (3.2 times more likely) showed the strongest correlation. These two countries also had the lowest rate of prevalence of early cannabis use; it is possible that deviation from this norm plays a part in the onset of depression. The association found for all countries together did not change after correction for a series of other mental health problems and for continuing cannabis use after the age of 17.
In a number of countries, behavioural problems in childhood or early adolescence were also measured. The association for these countries together was found not to be significant, once the behavioural problems were taken into account. It would appear therefore, that the tendency to break rules during youth could be responsible for the association that was found between early cannabis use and the later development of depressive symptoms.
Graaf R de, Radovanovic M, Laar M van, Fairman B, Degenhardt L, Aguilar-Gaxiola S, Bruffaerts R , De Girolamo G, Fayyad J, Gureje O, Haro JM, Huang Y, Kostychenko S, Lépine JP, Matschinger H, Medina Mora ME, Neumark Y, Ormel J, Posada-Villa J, Stein DJ, Tachimori H, Wells JE, Anthony JC. Early cannabis use and estimated risk of later onset of depression spells. Epidemiological evidence from the population-based WHO World Mental Health Survey Initiative. American Journal of Epidemiology 2010; 172: 149-159
Contact: Ron de Graaf
