Mayo Clinic Health Library

Alli weight-loss pill: Does it work?

Updated: 02-11-2012
Photo of Donald Hensrud, M.D.
Donald Hensrud, M.D.

Alli (pronounced AL-eye) is meant for overweight adults who are struggling to shed excess pounds. With its easy access and weight-loss promises, is Alli your answer to losing weight permanently?

Here, Donald D. Hensrud, M.D., a preventive medicine and nutrition specialist at Mayo Clinic, Rochester, Minn., answers common questions about Alli.

What is Alli?

Alli is the reduced-strength version (60 milligrams vs. 120 milligrams) of orlistat (Xenical), a prescription drug to treat obesity. It's approved for over-the-counter sale to overweight adults 18 years and older. Alli is meant to be used in conjunction with a low-calorie, low-fat diet and regular exercise.

What are the concerns with Alli?

In 2009, the Food and Drug Administration (FDA) began a safety review of orlistat because of rare reports of serious liver injury in people using it. The FDA found no cause-and-effect relationship between orlistat and the risk of liver injury. However, Alli and Xenical labels now advise people to be alert to signs and symptoms that could indicate liver injury, such as itching, loss of appetite, yellow eyes or skin, light-colored stool, or brown urine.

How does Alli work?

Alli promotes weight loss by decreasing absorption of fat by the intestines, which reduces the number of calories you absorb.

Lipase, an enzyme found in the digestive tract, helps break down dietary fat into smaller components, so it can be used or stored for energy. Alli works by disabling lipase, which prevents the enzyme from breaking down the fat while it's in your digestive tract. The undigested fat continues through the intestines and is eliminated through bowel movements.

Alli is taken with fat-containing meals, up to three times a day. Because of how Alli works, it's recommended that you eat no more than 15 grams of fat with each meal. Eating greater amounts of fat can cause unwanted effects, such as urgent bowel movements, diarrhea and gas with oily spotting.

How much weight could I lose using Alli?

Alli can help you lose weight, but the weight loss will likely be modest — perhaps just a few pounds more than you would lose with diet and exercise alone.

The average weight loss for prescription-strength Xenical is about 5 to 7 pounds (about 2 to 3 kilograms) greater than diet and exercise alone after one year. (2, 4) The lower dose Alli could conceivably result in a loss of 3 to 5 pounds (about 1 to 2 kilograms) a year in addition to the weight loss you could expect from diet and exercise alone.

What are the side effects?

You may experience bowel changes when taking Alli. These side effects can include:

  • Gas with an oily anal discharge
  • Loose stools or diarrhea
  • More-frequent bowel movements
  • Hard-to-control bowel movements

These bowel changes result from the undigested fat going through your digestive system. You can limit the side effects by eating a low-fat diet.

When shouldn't you take Alli?

Don't take Alli if you:

  • Are at a healthy weight
  • Are taking cyclosporine (Neoral, Sandimmune, others)
  • Have had an organ transplant
  • Have problems already absorbing food

Talk with your doctor about whether using Alli would be appropriate if you take blood-thinning medication or have diabetes or thyroid disease.

Orlistat decreases the absorption of certain fat-soluble vitamins — for example, vitamins A, D and E. If you're taking Alli, you need to take a daily vitamin supplement (at a time different from when you take Alli) to prevent potential nutrient deficiencies.

How long do I need to take Alli?

According to the manufacturer, most weight loss occurs within the first six months. Many people who take medications to lose weight regain the weight they lost when they stop taking the medication. Therefore, to keep the weight off, many people continue taking medications indefinitely along with eating a low-calorie diet and exercising regularly.

How does Alli fit into a healthy weight-loss plan?

As you consider Alli as a weight-loss aid, make sure that you make every effort to exercise, change your eating habits and adjust any other lifestyle factors that have contributed to your excess weight. Alli isn't the easy answer to weight loss and is meant only to supplement — not replace — a healthy diet and regular exercise.

Work with your doctor to evaluate the potential benefits and risks of Alli or any other weight-loss drugs. As a team, you and your doctor can create the most effective weight-loss plan for you.

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