Research from the Netherlands finds, in a nationwide survey of 1929 young adults, that cigarette smoking and cannabis were equally strongly associated with the frequency of psychotic-like experiences (PLEs). Further, though cannabis use was associated with distress from PLEs when cigarette smoking was eliminated as a confound, the inclusion of cigarette smoking rendered the statistical effect of cannabis on distress insignificant.
van Gustal, W., MacCabe, J., Schubart, C., Vreeker, A., et al.; Cigarette smoking and cannabis use are equally strongly associated with psychotic-like experiences: a cross-sectional study in 1929 young adults. Psychological Medicine. November, 2013 43(11):2393-401. doi: 10.1017/S0033291713000202. Epub 2013 Feb 18.
Of further interest:
Cigarette Smoking ‘Could Make You Psychotic’ (Huffington Post)