Cannabinoid type 1 receptor antagonists for smoking cessation.

BACKGROUND

Selective type 1 cannabinoid (CB1) receptor antagonists may assist with smoking cessation by restoring the balance of the endocannabinoid system, which can be disrupted by prolonged use of nicotine. They also seeks to address many smokers' reluctance to persist with a quit attempt because of concerns about weight gain.

OBJECTIVE

To determine whether selective CB1 receptor antagonists (currently rimonabant and taranabant) increase the numbers of people stopping smoking To assess their effects on weight change in successful quitters and in those who try to quit but fail.

METHODS

We searched the Cochrane Tobacco Addiction Review Group specialized register for trials, using the terms ('rimonabant' or 'taranabant') and 'smoking' in the title or abstract, or as keywords. We also searched MEDLINE, EMBASE, CINAHL and PsycINFO, using major MESH terms. We acquired electronic or paper copies of posters of preliminary trial results presented at the American Thoracic Society Meeting in 2005, and at the Society for Research on Nicotine and Tobacco European Meeting 2006. We also attempted to contact the authors of ongoing studies of rimonabant, and Sanofi Aventis (manufacturers of rimonabant). The most recent search was in January 2011.

METHODS

Types of studies Randomized controlled trialsTypes of participants Adult smokersTypes of interventions Selective CB1 receptor antagonists, such as rimonabant and taranabant. Types of outcome measures The primary outcome is smoking status at a minimum of six months after the start of treatment. We preferred sustained cessation rates to point prevalence, and biochemically verified cessation to self-reported quitting. We regarded smokers who drop out or are lost to follow up as continuing smokers. We have noted any adverse effects of treatment.A secondary outcome is weight change associated with the cessation attempt.

METHODS

Two authors checked the abstracts for relevance, and attempted to acquire full trial reports. One author extracted the data, and a second author checked them.

RESULTS

We found three trials which met our inclusion criteria, covering 1567 smokers (cessation: STRATUS-EU and STRATUS-US), and 1661 quitters (relapse prevention: STRATUS-WW). At one year, the pooled risk ratio (RR) for quitting with rimonabant 20 mg was 1.50 (95% confidence interval (CI) 1.10 to 2.05). No significant benefit was demonstrated for rimonabant at 5 mg dosage. Adverse events included nausea and upper respiratory tract infections. In the relapse prevention trial, smokers who had quit on the 20 mg regimen were more likely to remain abstinent on either active regimen than on placebo; the RR for the 20 mg maintenance group was 1.29 (95% CI 1.06 to 1.57), and for the 5 mg maintenance group 1.30 (95% CI 1.06 to 1.59). There appeared to be no significant benefit of maintenance treatment for the 5 mg quitters. One trial of taranabant was not included in our meta-analyses, as it followed participants only until end of treatment; at eight weeks it found no benefit for treatment over placebo, with an OR of 1.2 (90% CI 0.6 to 2.5). For rimonabant, weight gain was reported to be significantly lower among the 20 mg quitters than in the 5 mg or placebo quitters. During treatment, overweight or obese smokers tended to lose weight, while normal weight smokers did not. For taranabant, weight gain was significantly lower for 2-8 mg versus placebo at the end of eight weeks of treatment. In 2008, post-marketing surveillance led the European Medicines Agency (EMEA) to require Sanofi Aventis to withdraw rimonabant, because of links to mental disorders. The development of taranabant was also suspended by Merck & Co because of unacceptable adverse events.

CONCLUSIONS

From the trial reports available, rimonabant 20 mg may increase the chances of quitting approximately 1½-fold. The evidence for rimonabant in maintaining abstinence is inconclusive. Rimonabant 20 mg may moderate weight gain in the long term. Taranabant 2-8 mg may moderate weight gain, at least in the short term. In 2008, development of both rimonabant and taranabant was discontinued by the manufacturers.