After a joint do you believe you are Napoleon? Or Julius Caesar?

That's normal, as cannabis drugs are known to induce psychotic illnesses like schizophrenia. Now they have discovered how.

King's College London researchers found that cannabis's active ingredient tetrahydrocannabinol (THC) disinhibits brain areas that control aggressiveness and unsocial behavior while another cannabis chemical, cannabidiol (CBD), oppositely, keeps down psychotic symptoms. But THC levels have doubled in street cannabis in recent years, as it is a more potent addictive, from 6 % to 12 %.
In the UK there are estimated about 500,000 cannabis addicts.

After receiving THC, CBD or placebo capsules, healthy adult male subjects carried out brain scans and other tests.
THC induced decreased activity in the inferior frontal cortex, the brain zone that keeps down inappropriate thoughts and behavior, like swearing and paranoia. The symptoms were temporary but varied amongst individuals.

"Proving a long-term effect was extremely difficult, as it was not ethical or feasible to stimulate long-term psychosis in volunteers. However, if something has an active effect in inducing the symptoms of psychosis after one dose, then it would not be at all surprising if repeated use induced the chronic condition." said Professor Robin Murray, a consultant psychiatrist.
The new high potency cannabis represents a much higher health risk to health than the weaker previous types.

"It is similar to comparing the effect of drinking a glass of wine at the weekend with drinking a bottle of vodka every day." said Murray.

"We strongly urge the government to heed the growing evidence and take urgent action to warn young people that some of them are risking lifelong mental illness - that they are playing Russian roulette with their minds." said Marjorie Wallace, of the mental health charity Sane.

A Yale University research found that intravenous THC administration, even in small doses, induced psychosis symptoms in 50% of healthy subjects and those with a previous history of psychotic symptoms were the most predisposed.