Using rimonabant at a dose of 20 mg per day can help people quit smoking, can help them to remain abstinent, and can help prevent the weight gain that so often accompanies attempts at stopping smoking. The lower dose of 5mg, however, was not shown to be effective.
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.
One potential way of preventing this is to take a drug that blocks the receptor that is involved in nicotine's action in the brain - the cannabinoid 1 receptor.
These CB1 receptor antagonists could therefore form part of a therapeutic programme aimed at helping individuals quit smoking, although this drug has not yet been approved as a smoking cessation treatment in the USA or in Europe.
To see whether there was evidence that these receptor antagonists work two Cochrane Researchers, Kate Cahill who works at the Department of Primary Care in the University of Oxford and Michael Ussher who works at St George's, University of London, searched the published and unpublished literature for relevant research projects.
They found three trials that involved a total of 1567 smokers and 1661 people who had recently quit smoking. Analysing the data showed that the effect of the drug depended on the dose used:
Quitting with 20mg rimonabant:
People given 20 mg rimonabant increased by 50% their odds of remaining abstinent compared with those on placebo. Smokers who had quit while using 20mg rimonabant increased by 50% their odds of staying abstinent if they continued taking either 5mg or 20mg rimonabant, compared with those who moved to placebo treatment after quitting.
Quitting with 5mg rimonabant:
People who wanted to quit appeared to gain no benefit from 5 mg rimonabant treatment. Furthermore the people who did manage to quit using this lower dose were equally likely to remain abstinent whether they continued with rimonabant treatment or moved to a placebo.
Weight gain appeared to be significantly lower in people who quit while using 20 mg rimonabant than those taking either 5 mg rimonabant or placebo.
The differences in weight between the groups appeared to be maintained through longest follow-up. 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 20mg rimonabant may significantly increase a person's likelihood of quitting and may also reduce the amount of weight that they gain," says Cahill.