N. Dekker, J.H. Meijer, M.W. Koeter, W. van den Brink, N.J.M. van Beveren, G.R.O.U.P Investigators (Genetic Risk and Outcome of Psychosis authors: R.S. Kahn, D.H. Linszen, J. van Os, D. Wiersma, R. Bruggeman, W. Cahn, L. de Haan, L. Krabbendam, I. Myin-Germeys)
Submitted for publication.
Since early age at onset of psychotic illness is associated with poor outcome (Lauronen et al 2007) and with more frequent hospitalizations over the course of illness (Rabinowitz et al 2006), better insight in factors that are associated with an early age of onset of psychotic disorders is important. One of the factors associated with an earlier age at first psychotic episode is cannabis use (Buhler et al 2002, Veen et al 2004, Barnes et al 2006, Mauri et al 2006, Addington and Addington 2007, González-Pinto et al 2008, Barrigon et al 2009, Ongur et al 2009, Sugranyes et al 2009, Foti et al 2010, Pelayo-Terán et al 2010, De Hert et al 2010, Large et al 2011). In a recent meta-analysis, the mean age at onset of psychosis was 2.70 years lower in cannabis users compared to non-users (Large et al 2011). However, some studies did not find differences in age at onset of psychosis between cannabis users and non-users (Bersani et al 2002, Goldberger et al 2010, De Rosse et al 2010).