Most severely overweight patients taking anti-obesity drugs will realize only modest weight loss, especially if they fail to augment the medications with regular exercise and a healthy diet, say Canadian researchers.

They reviewed numerous studies on the drugs' effectiveness.

Despite being touted in the marketplace as miracle pills that can melt away pounds, the medications are no panacea to society's growing obesity epidemic, doctors say, and should only be taken by certain people.

"I think the most important thing that people need to understand is these are definitely not magic pills," said Dr. Raj Padwal, an assistant professor of internal medicine at the University of Alberta and principal author of the review.

Padwal and his colleagues looked at the results of 30 clinical trials of three drugs recommended for obese patients for long-term use — orlistat, sibutramine and rimonabant — and found that they helped people shed on average less than 11 pounds.

"We found that the amount of weight loss on average with these medications ranges between three and five kilograms," Padwal, who specializes in treating hypertension and obesity, said from Edmonton.

Orlistat (Xenical) reduced patients' weight by 6.4 pounds, sibutramine (Meridia) by about nine pounds and rimonabant (Acomplia) by just over 10 pounds in the studies, which each lasted at least a year. Participants had a mean weight of 220 pounds, with a body mass index (BMI) of 35. A BMI of over 30 is considered obese.

In their analysis published in Friday's issue of the British Medical Journal, the researchers showed that those given one of the drugs were significantly more likely to achieve the minimum weight loss target of five to 10 per cent than those given a dummy pill.

Drugs have side-effects

Although the drugs overall can be beneficial in reducing risk factors for cardiovascular disease and diabetes, they have differing side-effects that in some cases can be detrimental, Padwal pointed out.

For some people, sibutramine can significantly boost blood pressure; rimonabant — which is commonly prescribed in the U.K. and some European countries but not approved in Canada or the United States — can elevate the risk of mood disorders such as depression.

Padwal said getting patients to stick with any of the three weight-loss drugs long-term is a challenge.

"There's a large disconnect between what patients want in terms of weight loss and what practitioners desire," he said. "So patients will often want to lose … about 30 to 40 per cent of their initial weight. They want to get down to the weight they were in high school, two to three decades earlier."

"And they're disappointed when they're told that's going to be difficult to achieve."

Cost is also a major factor: orlistat and sibutramine (the only medications approved in Canada) will set patients back $80 to $130 per month, he said.   

Patients may also stop taking the drugs because of adverse effects such as gastrointestinal upset, anxiety or headaches.

But one of the biggest reasons patients fail to stick to their weight-loss regime, said Padwal, is the health-care system's failure to provide proper followup for Canadians battling obesity.

"We don't make it easy for individuals to see their practitioner if they want to have a visit regarding lifestyle changes or dietary counselling. And I think if people have to wait one to two hours to get in to see their doctor, it's unrealistic to think patients are going to come to us and wait that long for a medical assessment and counselling."