Professor Mary Cannon is a Professor of Psychiatric Epidemiology and Youth Mental Health in the Royal College of Surgeons in Ireland (RCSI).
From her research, which includes involvement in the Dunedin longitudinal study, Professor Cannon warns that cannabis is strongly associated with psychotic symptoms and psychotic disorders such as schizophrenia. In fact, cannabis use is now the most powerful single environmental risk factor for psychotic disorder.
Recent studies from Europe have examined the risks associated with high-potency cannabis (defined as greater than 10 per cent THC) and have found that daily users of high potency cannabis have a nine-fold increased risk of developing schizophrenia or another clinical psychotic disorder. But this “psychotogenic” effect is not confined to adolescent-onset cannabis use and appears more linked to frequency of use. In addition, it is not confined to people with a history of psychotic disorder in their family (although they are at high risk and should avoid cannabis). It has been estimated that between one third to half of all the cases of psychotic illness in places like London or Amsterdam could be due to cannabis.
The failure of governments worldwide to control alcohol harms shows that once an addictive substance is legalised and freely available public health takes a second place to profit.
She talks to Say Nope To Dope spokesperson Aaron Ironside about the effects of legalisation of marijuana in the US, and why he’s encouraging New Zealanders to vote NO in the upcoming referendum.