Teenagers who use cannabis and have a family history of mental illness are 25 percent more likely to suffer from schizophrenia, delusions and paranoia than their peers who don't use the drug. Adolescents with no mental illness in their background are also six percent more likely to develop these symptoms than non-users.
This is according to a study that monitored 2,500 youths in Germany. Jim van Os of the Maastricht University in the Netherlands led the study. The results were published in the online British Medical Journal, and helped show that the link between cannabis and psychosis was not just that psychotics were more likely to smoke the chemical-laden plant than other people.
The study also showed that the more you smoke, the higher the chances are of developing mental problems. According to van Os "if you are vulnerable, then the more cannabis you use, the greater your risk of psychosis."
The main psychoactive ingredient in dagga is THC (delta-9-tetrahydrocannabinol), and this chemical is thought to be the root of the negative mental side effects of the drug. It causes the release of dopamine, which initially causes pleasure but can later lead to paranoia.
The levels of THC in cannabis vary from source to source. According to van Os, older hippies are used to two or three percent THC in their pot, whereas today concentrations can reach 20 percent.