The pharmaceutical rimonabant latches on to the cannabinoid 1 (CB1) receptors in the brain and blocks their activity. Cannabinoid receptors are normally stimulated by natural chemicals in the body but also, as the name might suggest, by compounds in cannabis and in tobacco smoke.

Now, a Cochrane Systematic Review has revealed that a dose of rimonabant as low as 20 milligrams, but not less than that, can selectively block the CB1 receptors in smokers, and so preclude the apparently pleasant feelings they would normally get from smoking a cigarette. However, unlike other efforts at inducing smoking cessation, rimonabant does not lead to food cravings that often lead to quitters gaining weight in the weeks and months after they stop smoking.

Smoking tobacco sends nicotine into the blood stream, and this chemical disrupts the endocannabinoid system, part of the hormonal control mechanism in the brain that controls energy balance and food intake. Over time the body alters the nature of its energy mechanism to compensate for this effect. Stopping smoking removes the nicotine and once again disturbs the mechanism, adding to the withdrawal symptoms and leaving a person prone to put on weight.

Kate Cahill of the Department of Primary Care at the University of Oxford and Michael Ussher of St George's Hospital Medical School, University of London, undertook a search of all the published and unpublished scientific literature pertaining to rimonabant to uncover evidence of efficacy in stopping smoking without weight gain.

They found three medical trials that involved a total of 1567 smokers and 1661 people who had recently quit smoking. They analyzed the data and found that people given 20 mg of rimonabant were 50% more successful at quitting cigarettes than people on placebo. Those who had already quit, stayed off cigarettes if they took either 5mg or 20mg of rimonabant. However, smokers hoping to quit given just 5mg of rimonabant to begin with, appeared to gain no benefit.

The team also found from their analysis of the trials that weight gain was much lower in smokers who quit while receiving 20 mg of rimonabant compared to anyone on just 5 mg rimonabant or placebo. This beneficial effect was more evident in overweight or obese smokers than in those of normal weight.

"From the preliminary data that we found it appears that 20 mg rimonabant may significantly increase a person's likelihood of quitting and may also reduce the amount of weight that they gain," says Cahill.

The drug is yet to be approved as a smoking cessation treatment in the USA or Europe.

http://dx.doi.org/10.1002/14651858.CD005353.pub2

http://www.primarycare.ox.ac.uk/research/cochrane/
staff/cahill

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