Rimonabant anti-cannabinoid addiction treatment clinical trials

The Langton Centre, a specialist outpatient clinic for drug and alcohol treatment attached to Sydney Hospital, initiated a study this year of a possible new drug treatment for cannabis addiction. Currently the only treatment is counselling.

The drug, Rimonabant, is a cannabis-receptor antagonist marketed in Australia as the weight loss drug Accomplia. It blocks the receptors in the brain where cannabis acts, so cannabis has a diminished or no effect when people are taking it. Twelve volunteers enrolled, all of whom are participants in rehabilitation programs run by the Ted Noffs Foundation and three government treatment clinics. Participants, whose average age was 26, were offered a daily 20-milligram tablet of Rimonabant for up to 3 months.

Dr Mark Montebello and Dr James Bell, who initiated and conducted the three-month study, knew it was fraught with difficulties. They recruited mainly people with a history of mental illness - heavy cannabis users, smoking on average 26 out of 28 days before they joined the rehabilitation programs. Although Rimonabant is available in Australia, the US Food and Drug Administration has so far refused to approve its use because of adverse side effects in clinical trials, including an increase in anxiety and depression.

Bell, an addiction medicine physician and director of the drug and alcohol program for the South Eastern Sydney Area Health Service, says there has not been a clinical trial reported anywhere of Rimonabant's potential as a treatment for cannabis addiction.

Two volunteers were hospitalised for psychiatric illness during the study, but Bell does not believe Rimonabant was the cause. Those remaining in the trial were tracked for six months, and the results, reported late last year at a conference in New Zealand, showed that most participants had a marked reduction in cannabis use (which was verified by urine tests).

Bell and Montebello are evaluating the results, which appear encouraging, and preparing them for publication. "I am not trying to talk up this drug as a treatment. Treating cannabis dependence is difficult, and while in our trial Rimonabant helped some individuals to interrupt heavy cannabis use, it also caused many side effects, and people took it mostly for short periods. I don't want mothers ringing me, hoping it's a cure for their sons. If we are to proceed to larger clinical trials, against a placebo, we would use it as a short-term initial intervention, to be followed with longer-term counselling."

Although it is used in Australia, Acomplia did not meet FDA approval for use as a weight-loss aide in the US.