Teenagers and young adults who, in the words of the BBC, "use cannabis," are increasing their risk of psychosis, according to a new study. Of course, the link between psychosis and marijuana use is well-documented (remember that kid from high school? Who smoked all that weed? And then a few years later he left you a voicemail letting you know that he was in touch with the German Chancellor about the second coming?)—this study, however, seems to indicate that cannabis usage comes first, and not as a self-medication strategy for symptoms of psychosis:
The participants in the study, aged between 14 and 24, were assessed for cannabis use and psychotic symptoms at three points over a ten-year period.
It found that cannabis use "significantly" increased the risk of psychotic symptoms, even when other factors such as socio-economic status, use of different drugs and other psychiatric conditions were taken into account.
Of course, from what I can tell from the article, the fact that cannabis use comes first doesn't necessarily mean that it causes psychosis—those prone to psychosis may also be prone to drug use for a variety of reasons.