A chemical found in cannabis could be used to treat schizophrenia with fewer side-effects than existing antipsychotic drugs, research suggests.

Though cannabis can provoke psychotic symptoms, these effects appear to be caused chiefly by one of its components; and another compound that damps down its effects has potential as a medicine, scientists said.

The findings, to be announced at a conference that opens in London today, offer a possible explanation for anecdotal reports of increasing cases of psychosis and schizophrenia triggered by the drug.

As concentrations of tetra-hydracannabinol (THC), the main psychoactive element that can provoke psychosis, have risen, levels of the beneficial chemical, cannabidiol (CBD) have fallen. This could mean that users are being exposed to higher doses of the damaging chemical, while receiving less CBD, which tends to balance THC’s effects.

“There is a possibility that there are good guys and bad guys in cannabis,” said Markus Leweke, of the University of Cologne.

“THC is the bad guy, but there is a small body of literature that suggests CBD may prevent the induction of psychotic symptoms. Our study supports that view.”

There are no official statistics on how cannabis use is affecting levels of mental illness, but there is growing evidence that the drug can induce psychosis and schizophrenia.

Scientists also report anecdotal evidence that more young people are developing schizophrenia as a result of using the drug. Robin Murray of the Institute of Psychiatry, said: “There is no robust evidence on cannabis-induced psychosis, but there are a lot of anecdotal reports it is increasing. Psychiatrists specialising in adolescence who used to have no interest in psychosis are now holding clinics with lots of patients with psychosis related to drug use.”

Comparisons of US drugs seizures in the 1960s and the 1990s show that THC levels have increased significantly as growers breed plants with more powerful psychoactive effects, and it is known that CBD content goes down as THC increases.

In the research, which will be presented at the Institute of Psychiatry’s international conference on cannabis and mental health, Dr Leweke investigated the effects of CBD on 42 patients with acute schizophrenia. Some were given CBD, while others received a standard anti-psychotic drug called amisulpride. Both groups had fewer psychotic symptoms, but the CBD group also experienced fewer side-effects. Common side-effects of amisulpride include weight gain, sexual dys-function and liver problems.

In two studies to be presented to the conference, scientists have found new evidence linking THC to psychosis. Philip McGuire and Zerrin Atakan, of the Institute of Psychiatry, used functional magnetic resonance imaging to scan the brains of patients who took THC, and found that it reduced activity in a region involved in inhibiting inappropriate behav-iour. As activity in this region dropped, the subjects became progressively more paranoid.

A second study, by Deepak Cyril D’Souza, of Yale University, found that THC administered intravenously worsened the symptoms of patients with schizophrenia.

High points

— The average cannabis plant contains about 60 components and 400 chemicals

— Cannabidiol (CBD) is the only nonpsychoactive component; delta-9-THC is the most psychoactive component of cannabis

— The “high” is caused mainly by delta-9-THC binding to cannabinoid receptors in the brain

— About two million people in Britain smoke cannabis, and about 15 million admit to having tried it

— Half of all 16 to 29-year-olds have tried it at least once

— About 11 per cent of adults (13,000) and 67 per cent of 11 to 17-year-olds (9,600) admitted for drug treatment had symptoms associated with cannabis

Sources: Royal College of Psychiatrists; University of New South Wales

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