Cannabis and psychosis

There is growing evidence reliably linking cannabis with mental health problems. However, it remains unclear whether cannabis actually causes mental illness, or whether many people with mental illness are pre-disposed towards cannabis use.

Some claim cannabis causes schizophrenia. Research suggests that for people who are already at risk of developing schizophrenia, cannabis can cause the onset of psychotic symptoms. For this reason, people with a vulnerability to schizophrenia (such as a family history of mental illness) should avoid using cannabis completely.

Cannabis use, particularly heavy and frequent use, has been linked to a condition called 'cannabis psychosis'. Episodes of cannabis psychosis are characterised by delusions, confusion, memory loss and hallucinations and could last several days.

An Australian study, published 2006 in the British Journal of Psychiatry, showed that the more cannabis a person with mental illness uses, the worse their symptoms become. It also found that when they suffer a relapse in psychotic symptoms, they were more likely to self medicate with cannabis to cope.

Recent research suggests the earlier regular cannabis use occurs  and the heavier it is smoked, the more likely it is to harm development, achievement, and behaviour, while increasing risk of mental health problems.