Scientists are developing a pill that helps people quit smoking and slim down at the same time.
Obesity is a major killer
The drug, rimonabant, works by blocking the circuits in the brain that control the urge to eat and smoke.
Obesity and smoking have become two of the world's biggest killers, and are being targeted for action in the UK.
The makers, French firm Sanofi-Synthelabo, hope to market the drug next year.
In one trial the drug helped people to shed an average of 9kg (20lbs) in a year.
And in a second, it was found to double the chances of smokers successfully quitting - at least in the short term.
Dr Robert Anthenelli, of the University of Cincinnati, who directed the smoking study, said: "We think this might be the ideal compound for people who are overweight and smoke."
The drug works by blocking the endocannabinoid system in the brain which regulates hunger, and probably other urges, including craving for alcohol.
The drug marijuana makes people ravenous by stimulating this circuitry.
And it is thought that over-eating and smoking can also over stimulate this system, leading people to eat and smoke still more.
Rimonabant seems able to block the body's ability to receive these signals, allowing the system to return to normal.
The obesity arm of the research focused on 1,036 overweight volunteers, who were put on a restricted calorie diet, and given either rimonabant or dummy pills.
After a year, those who got the higher of two doses of rimonabant had trimmed 7.6 centimetres (three inches) from their waistlines. Nearly half of them took off 10% of their body weight.
Those on placebos lost just 2.25 kilograms (five pounds).
Rimonabant also seemed to cut levels of potentially harmful cholesterol, while boosting levels of "good" cholesterol.
People taking the drug reported that they simply felt less hungry.
Dr Jean-Pierre Despres, of Laval University in Quebec City, who led the obesity study, said: "The bottom line is we found a spectacular drop in waistlines and changes in many other risk factors that are beyond what you would ordinarily expect."
The smoking arm of the study showed 28% of smokers who took the drug shunned cigarettes for at least a month, compared to just 16% who were given dummy pills.
The people on rimonabant who quit gained little or no weight - and a third actually slimmed down.
Dr Ian Campbell, chairman of the UK National Obesity Forum, told BBC News Online that the drug "looked promising".
"It appears to have helped patients maintain significant weight loss over a 12 month period, but I look forward to even longer term results.
"However, I would stress that weight management remains a lifestyle issue. Medication must only ever be seen as an adjunct to support people who have made efforts to change their lifestyle first."
Dr Campbell said people who gave up smoking had a tendency to put on weight, and this put many people off even trying.
"A drug which could tackle both problems would represent a fantastic opportunity," he said.
Dr Gareth Pryce, who has conducted research into cannabinoids at the Institute of Neurology, London, expressed concern that the drug might not be safe for some patients to take.
He said: "My group has carried out animal research that showed interference with the cannabis receptor in the brain may have a damaging effect on the progression of multiple sclerosis.
"There are also concerns about the possible impact on people who have a stroke, or head injury while taking the drug.
"My other concern is it could exacerbate neurological diseases that had previously been clinically silent."
Details of the trials were presented at a meeting of the American College of Cardiology in New Orleans.