Diet drugs, such as Meridia, Xenical and rimonabant, can help shrink waistlines, but keeping that weight off may be the toughest part. Obesity can easily return once individuals quit exercising and eating right, or stop using a weight-loss medication.

Weight-loss pills "shouldn't be used alone," said Dr. Susan Yanovski, director of the Obesity and Eating Disorders Program at the US National Institute of Diabetes and Digestive and Kidney Diseases. She's also the author of a commentary on the Meridia (sibutramine) study, published in the Nov. 17 issue of the New England Journal of Medicine.

"The real take-home message from this article is that when you combined lifestyle modification with the weight-loss drug, you lost twice as much weight," she said. "You lost more than 26 pounds with combined treatment vs. 11 pounds with sibutramine alone."

Lifestyle Changes

Meridia is just one of two weight-loss drugs currently approved for use by the US Food and Drug Administration, the second being Xenical (orlistat). A second article in the same issue of the journal found promising results for a third medication, rimonabant, which is currently undergoing FDA review.

Most obesity experts say lifestyle changes, especially improved diet and exercise, are the real keys to shedding excess pounds. But Dr. Thomas Wadden, director of the Weight and Eating Disorders Program at the University of Pennsylvania Medical School, said many overweight Americans still find it tough to lose weight.

"There's nothing worse than to be watching your calories and exercising, but the scale just doesn't budge," said Wadden, who was also lead researcher on the Meridia-plus-lifestyle study. "You just feel like, 'My efforts are for naught.' That's when people tend to give up."

And that's when diet pills may come in handy, according to Yanovski. "All the weight-loss drugs have shown generally what I'd consider a modest weight loss compared with placebo, usually in the range of five to 15 pounds additional weight loss," she said.

Few studies have focused on whether this modest weight loss might be improved upon if diet-pill users also switched to low-calorie diets and exercised more.

'Don't Look for a Quick Fix'

In its one-year trial, Wadden's team randomly assigned 224 obese adults to either 15 milligrams of Meridia per day or the same dose given in conjunction with counseling on how to drop weight through environmental changes, improved diet and exercise.

Among other things, the counseling "teaches you how to stay away from all-you-can-eat buffets and fast-food restaurants, gets you to keep food records and to shop from a [healthy foods] list," Wadden explained.

These changes, along with a healthy diet and physical activity, "[help] you modify the external environment," Wadden said, while drugs such as Meridia "help modify the internal environment" as they work on brain chemicals to lower appetite and help patients feel fuller sooner.

The combination seems to work: According to the researchers, people taking Meridia who also changed their lifestyles lost double the amount of weight compared to those who took the drug but made no lifestyle changes.

The bottom line? When it comes to obesity, "Don't look for a quick fix from the drug store," Yanovski said. "Combining therapy seems to be much more effective than drug treatment alone."

Experimental Drug Rimonabant

A second study in the journal looked at the potential of an experimental drug, rimonabant, in helping obese individuals shed weight over the course of one year.

"Rimonabant is a little bit different in that it acts not only on the brain but also on other tissues in the body, such as fat cells and those in the gastrointestinal tract," Yanovski said.

The international study was led by Jean-Pierre Despres of Laval University in Ste.-Foy, Quebec, Canada, and involved more than 1,000 overweight or obese patients with untreated high cholesterol. Participants were given either daily rimonabant (at doses of 5 milligrams or 20 milligrams) or a placebo, and were also placed on a low-calorie diet.

The researchers reported that rimonabant did help users lose an average of just under seven kilograms (15 pounds) over one year. And the drug may have an added health benefit, since it also seemed to lower levels of dangerous blood fats known as triglycerides while boosting blood levels of HDL "good" cholesterol.

"We know that it improves [cardiovascular] risk factors, but we don't know yet if that translates into a reduction in heart disease or death," Yanovski said.

The Toughest Part

While drugs such as Meridia, Xenical and rimonabant can help shrink waistlines, keeping that weight off may be the toughest part, Wadden said. Study after study has shown that obesity can easily return once individuals quit exercising and eating right, or stop using a weight-loss medication.

"We now realize that people may have to take weight-loss medications on a long-term basis," Wadden said, "just like they have to take other medications, such as those that control cholesterol or high blood pressure."

In the case of Meridia, that means long-term physician monitoring, too, since the drug can trigger a rise in pulse rate and blood pressure in about 10 percent of users, the researchers said.

The Meridia study was supported by a grant from the National Institute of Diabetes and Digestive and Kidney Diseases, while the rimonabant study was funded by the drug's maker, Sanofi-Aventis.

A third study, appearing in the December Annals of Behavioral Medicine, found that people who get in the habit of weighing themselves each day are more successful at keeping obesity at bay.

The study involved more than 3,000 obese or overweight individuals enrolled in weight-loss programs for two years. Researchers at the University of Minnesota found that those who checked their weight daily lost more than those who didn't.

"If people see that their [weight] has gone up, they may realize it's time to do something. It's probably easier to make that small correction," lead researcher Jennifer Linde said in a prepared statement.

All that monitoring and hard work could pay off, though, since even minor weight loss can trigger major health benefits.

According to Wadden, "the Diabetes Prevention Program showed that if people lost just 7 percent of their initial body weight -- about 15 pounds through 150 minutes of exercise per week -- they reduced their risk of developing type 2 diabetes by 58 percent. A little bit of weight loss goes a long way."

More information: Find out more about obesity at the US National Institute of Diabetes and Digestive and Kidney Diseases.