The results appear to confirm a link between psychosis and skunk cannabis, which now accounts for 80 per cent of street seizures of the drug.
Scientists at the Institute of Psychiatry in King's College London made the discovery after running tests on 22 healthy men, aged in their late 20s.
They injected them with THC - a major component of skunk cannabis which has been blamed for increasing psychosis among heavy users.
By giving a dummy injection to some, and a dose of THC to others, the scientists were able to establish a link between THC and psychosis, in which hallucinations and delusions leave sufferers unable to tell between the real and imagined.
The team, led by Dr Paul Morrison, concluded: "These findings confirm that THC can induce a transient acute psychological reaction in psychiatrically well individuals."
The researchers found that the "extent of psychotic reaction" was not related to "the degree of anxiety or congnitive impairtment" in the men.
Mary Brett, vice president of Europe Against Drugs, said: "This shows that anyone who is healthy can become psychotic by smoking cannabis. They don't already have to have a mental illness. Healthy people can become psychotic."
The potency of skunk cannabis has increased from six per cent THC - or Delta-9-tetrahydrocannabinol - content in 1995 to 14 per cent in 2005, and has been linked to increased instances of psychosis, particularly among young men.
Today's skunk cannabis also contains virtually no traces of another chemical, called CBD (cannabidiol), which appears to counteract the damaging effects of THC.
The research is the first time that the dangers of skunk cannabis have been tested in the UK. Previous experiments have been run by experts in the US, Holland and Brazil.
Dr Morrison said the findings offered "additional evidence that can elicit temporary psychotic-like effects in some people", but stopped short of suggesting they proved a direct link between psychosis and THC.
He said: "Much more research is needed to clarify if skunk is actually more harmful than traditional cannabis." More work needed to be carried out on the beneficial effects of CBD in balancing the damaging results of THC.
Earlier this year then-Home Secretary Jacqui Smith restored cannabis from class C to class B status after concerns about adverse health effects, against the advice of her drugs advisers.
Last year The Daily Telegraph revealed how a BBC reporter Nicky Taylor was injected with THC at the institute. One source who witnessed the effects on Miss Taylor said the effect was "dramatic, it was unpleasant".
A survey of 200 users, published in July 2008, found that those who smoked skunk cannabis were 18 times more likely to develop psychosis than those who smoke milder forms of the drug.
A Home Office spokesman said: "We have always been clear that cannabis is a harmful drug which should not be taken. Its use can lead to physical and psychological harms, and the mental health effects of cannabis use are real and significant.
"We are taking comprehensive action to tackle cannabis use, from increased enforcement to reduce the supply, along with effective education and early intervention for those most at risk."
By Christopher Hope
July 27, 2009
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New Study: Cannabis 'can cause psychosis in healthy people'