How Alli Works to Help You Lose Weight

boxes of alli on a counter

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In This Article

Alli is an over-the-counter (OTC) diet pill approved by the U.S. Food and Drug Administration (FDA). It is the brand name for a medication called orlistat, which is perhaps better known by its prescription version's name Xenical. Alli is FDA-approved for use in overweight adults along with a reduced-calorie, low-fat diet and exercise. The diet pill is not an easy fix for weight loss, but it may help some people lose more weight and improve their health than lifestyle changes alone.

How Alli Works

Alli (orlistat) is a lipase inhibitor. It works by preventing your body from absorbing some of the fat that is in your food. You take the medication before each meal and it works in your intestines to remove about 25 percent of the fat consumed.

Excess fat is eliminated from your body in your stool. But that doesn’t mean you can indulge in fatty foods when you take Alli. The medication should only be used while you’re eating a balanced, low-calorie, and low-fat diet. That means that you’ll eat less than 30 percent of your total daily calories from fat and limit fat to 15 grams per meal.

Alli contains 60 mg of orlistat, while Xenical contains 120 mg of the drug and requires a prescription from your healthcare provider.


How much weight you can lose when you take Alli depends on a number of factors, including recommended lifestyle changes.

If you don't adhere to the recommended diet, you probably won’t lose weight. And if you don’t also exercise on a regular basis, any weight you do lose probably won’t stay off for good.

When researchers studied weight loss with orlistat, the results were mixed. For example, in one study cited by GlaxoSmithKline (the company that makes Alli), the medication helped 26 patients lose 5.6 percent of their total body weight in three months.

However, in another published study, researchers followed more than 100,000 orlistat users for three years. They found that although patients lost about 2 pounds per month in the first few months, they did not maintain significant weight loss over the long term.

Side Effects

According to the National Institutes of Health, the most common side effects of Alli involve changes to your bowel movements. They range from gas and loose or oily stool, to stomach cramps, oily spotting on your underwear, and difficulty controlling your bowel movements. 

Many Alli users who complain about side effects experience them in response to eating a high-fat meal, but even with a careful diet, some users can have problems.

Side effects generally subside after the first few weeks of taking the pill. If Alli side effects continue beyond that point, talk to your doctor.

Risks and Warnings

In addition to side effects, Alli may be harmful to your liver. In 2010, the FDA updated its requirements for the labeling of orlistat products to include safety information about a few cases of severe liver injury linked to the weight-loss pill. If you have a pre-existing liver condition or experience jaundice, severe itching, or dark urine, see your doctor.

As with all medications, take caution to purchase Alli from a reputable vendor and check the package closely before taking a pill. In 2014, product tampering was reported and resulted in a voluntary recall of the diet pills. Alli came back on the market with an updated package that makes it easier to see if the bottle has been opened.

Is It Right for You?

If you are thinking about taking Alli for weight loss, talk to your doctor. While a prescription is not required, you should not take orlistat if you have any of the following diagnoses:

  • Pregnancy
  • Cholestasis
  • Malabsorption syndrome
  • Anorexia nervosa
  • Bulimia
  • Diabetes
  • Kidney stones
  • Pancreatitis
  • Gallbladder disease
  • Thyroid disease

Your doctor is the best person to determine if the product is safe for you and how losing weight might improve your health.

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