de Graaf R, Radovanovic M, van Laar M, Fairman B, Degenhardt L, Aguilar-Gaxiola S, Bruffaerts R, de Girolamo G, Fayyad J, Gureje O, Haro JM, Huang Y, Kostychenko S, L?pine JP, Matschinger H, 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: Epidemiologic evidence from the population-based World Health Organization World Mental Health Survey Initiative. Am J Epidemiol. 2010 Jul 15; 172(2):149-59.