A British health charity called on Saturday for an investigation into evidence that smoking cannabis may cause psychosis in people at risk of mental illness.

Rethink, which campaigns on behalf of schizophrenia sufferers, said the mental health risks of using cannabis were not widely understood.

“There is strong evidence from a wide range of sources that long term and short-term use of cannabis can ‘trigger’ a psychotic episode of schizophrenia in people who are at high risk of developing schizophrenia—for instance, people who have close family members who have schizophrenia,” it said in a statement.

The organization pointed out that it was a year since the government reclassified cannabis from a Class B to a Class C drug, adding that a government awareness campaign that followed ignored the mental health dangers of using the drug.

“There is a general consensus that long-term, and in some cases short-term, use of cannabis by someone who has schizophrenia worsens the psychotic symptoms of the illness - paranoia, hallucinations and delusions,” it said.

The charity added that it believed many young people viewed cannabis as a risk-free drug.

“A long-term, well-funded, innovative campaign aimed at publicizing the real mental health risks associated with cannabis needs to be in place as soon as possible to counter the ‘risk-free’ message,” the statement said.

“Rethink is asking MPs and Peers to support further research into the links between cannabis and severe mental illness that focuses on its widespread use among young people, the increasing strength of cannabis on sale on the streets and its short and long-term effects on mental health.”