Weight Loss Drugs: How Much Do Diet Pills Help?

The truth about weight loss medications and supplements.

By Kathleen Zelman, MPH, RD/LD
WebMD Weight Loss Clinic - Feature

Reviewed By Louise Chang, MD

"Clinically proven to help you lose weight without being hungry or working out for hours at the gym!"

You've seen the ads promising successful weight loss by taking diet drugs or weight loss supplements, but do they really deliver results? Could weight loss medications and over-the-counter supplements really help to reverse the obesity epidemic?

Experts who spoke to WebMD agreed that there's no such thing as a quick fix or magic bullet when it comes to losing weight. Weight loss medications (not to be confused with dietary supplements) can help you lose weight, but only if you also cut calories and get moving. And effective weight loss, they say, is slow and gradual -- anywhere from 1/2 to 2 pounds per week, even with the help of diet drugs.

"Weight loss medications can be modestly effective, and enhance weight loss by 8%-10%, but medication does not work for everyone," says Robert Kushner, MD, a professor of medicine at Northwest University.

Kushner estimates that about a third of his patients respond well to medication. But he points out that drug therapy is only one part of a lifestyle that also includes a healthy eating plan, regular exercise, and behavior modification.

Louis Aronne, MD, director of the comprehensive weight control program at New York Presbyterian Cornell Weill Medical Center, agrees.

"Medications can really make a difference for some people, but it must be part of a complete lifestyle that includes diet and exercise," he says.

One problem, says Aronne, it is that there are simply not enough medications to choose from.

"We have numerous medications for conditions like high blood pressure, but when it comes to treating obesity we only have a few, and we could use 5-10 different types of weight loss drugs," he says.

Weight Loss Drugs and How They Work

There are two basic types of weight loss drugs -- prescription drugs, which have been around for years, and now, with the release of Alli, over-the-counter medication. Other over-the-counter weight loss remedies are considered dietary supplements; they do not undergo the same type of FDA approval process as drugs.

"Approved weight loss drugs must prove they are safe and effective with strong scientific evidence in order to pass the stringent FDA approval process," says Aronne, former president of the North American Association for the Study of Obesity (NAASO).

In the prescription drug category, there are basically three choices, Xenical (orlistat), Meridia (sibutramine), and phentermine.

Xenical (orlistat) is a fat blocker that prevents fat from being completely absorbed in the gastrointestinal tract. Prescription strength is 120 milligrams; over-the-counter Alli is the same drug at half strength, or 60 milligrams.

Fat blockers reduce fat absorption and, as a result, some people are plagued with oily discharge, fatty stools, gas, and/or inability to control bowel movements. These side effects are the result of the fat not being absorbed by the body. Eating a low-fat diet reduces the risk of potential side effects. But if your diet is already low in fat, you may see less of an impact from the medication, as there is less fat to block.

Xenical or Alli is safe for almost anyone because the drug is not absorbed, says Kushner. "I frequently prescribed it to cardiovascular patients because it is so safe," he says.

Patients must be willing to stick to a low-fat diet. These drugs have a built-in feedback system. "If you eat a high-fat diet, you will experience the side effects, so to avoid the unpleasant effects, you need to reduce the fat in your diet," says Aronne.

Not only do these drugs block fat, they have the potential to block other nutrients.

"Take a once-daily multivitamin mineral for nutritional insurance to help compensate for any losses and don't take it at the same time as the medication," says Dawn Jackson-Blatner, a spokesperson for the American Dietetic Association.

Meridia (sibutramine) helps reduce hunger by working on the appetite control center in the brain that makes you feel full.

"Meridia can help add 5%-10% additive weight loss that you would not get with diet and exercise alone" says Aronne.

Kushner prescribes Merida to patients who struggle with cravings and have trouble knowing when to stop eating. Aronne says that younger patients who are at a low risk for heart disease are good candidates.

Side effects include dry mouth, constipation, and insomnia. Meridia should not be used by anyone with cardiovascular risk factors.