Potent cannabis can cause psychosis in healthy people, a new British study has proved conclusively.

The results appear to confirm a link between psychosis and skunk cannabis, which accounts for 80 per cent of street seizures of the drug.

Scientists at the Institute of Psychiatry at King's College, London, made the discovery after tests on 22 healthy men in their late 20s.

They injected them with the chemical THC - a main component of skunk cannabis, which has been blamed for increasing psychosis among heavy users.

Scientists gave a dummy injection to some of the men and a dose of THC to others. They found a link between the chemical and psychosis, in which hallucinations leave sufferers unable to know what is real and what is imagined.

