You might have heard about — or seen big store displays of — the weight-loss pill "Alli" (pronounced: al-eye). Could it be the diet miracle you're waiting for?

Probably not.

Alli (generic name orlistat) is only for overweight adults. The U.S. Food and Drug Administration (FDA) and Alli's manufacturer both say that anyone younger than 18 should not use Alli. That's because experts aren't sure if it could interfere with the way a teen's body grows and develops, or if it might cause other health problems.

A prescription version of the same drug (called Xenical) is approved for use in people who are 12 or older — a doctor's prescription is required, so the drug can be used by teens only when under medical supervision.

Alli works by preventing a person's body from absorbing some of the fat that's in food. That may sound like a good thing — after all, when fat calories are not absorbed, there's no chance they can be stored in the body as extra pounds.

But not getting enough fat could interfere with normal growth and development in both girls and guys. Fat also helps the body absorb and process many of the vitamins we need for good health.

Some potentially unpleasant (and embarrassing) side effects go with taking Alli (the company calls these "treatment effects"). All that undigested fat has to go somewhere, and the only way for it to leave the body is as an oily discharge through the anus.

This means the following things could happen to someone taking the drug:

• gas (farting) with oily discharge that can leak out and stain clothing
• more frequent — or even uncontrollable — bowel movements
• looser, oilier bowel movements

Alli can also cause problems for people who have certain health conditions, such as diabetes, thyroid disease, gallbladder problems, or kidney stones.

Although Alli is approved as safe and effective for adults, it's no quick fix. For one thing, just like dieting, it takes time to lose weight with Alli. People who take the drug don't see instant results.

Taking Alli requires as much discipline and willpower as sticking to a diet: People using it have to keep careful track of the amount of fat they eat at each meal to be sure they don't get too much. Taking Alli with meals that contain more than 15 grams of fat can worsen the side effects mentioned above (15 grams is about the amount of fat in 2 tablespoons of peanut butter or one chocolate bar). So Alli is not a free pass to eat more fatty foods without gaining weight.

The bottom line is, when you're young, it's best to talk to a doctor about weight loss. Only a doctor can know your personal history — such as whether any recent weight gain is just a temporary part of the growing up process.

Reviewed by: Steven Dowshen, MD
Date reviewed: September 2010