Alli (Orlistat) - Oral

What Is Alli?

Alli (orlistat) is an orally administered over-the-counter (OTC) weight loss aid that is sometimes given through a prescription under a different brand name, Xenical. Alli is used along with a reduced-calorie and low-fat diet in medically overweight adults.

Orlistat (the primary ingredient) is used with an individualized low-calorie, low-fat diet and exercise program to help people lose weight. In comparison, prescription Xenical is used in overweight people who may also have hypertension (high blood pressure), diabetes, high cholesterol, or heart disease.

The medical definition of overweight is having a body mass index (BMI) of 25 to 29.9. BMI is calculated using your height and weight. BMI calculators and charts are available online.

Alli contains orlistat as its active ingredient. Orlistat belongs to a drug class known as lipase inhibitors. It works for weight loss by blocking your digestive system from absorbing fat from your diet. It helps your body get rid of the fat by eliminating it in your stool.

Alli is available OTC. It comes as a 60-milligram capsule that you take orally (by mouth). A higher strength of this drug, Xenical 120 milligram, is available by prescription.

Drug Facts

Generic Name: Orlistat

Brand Name(s): Alli, Xenical

Drug Availability: Alli (OTC), Xenical (prescription)

Administration Route: Oral

Therapeutic Classification: Lipase inhibitor

Available Generically: No

Controlled Substance: N/A

Active Ingredient: Orlistat

Dosage Form(s): Capsule


Body Mass Index (BMI) is a dated, biased measure that doesn’t account for several factors, such as body composition, ethnicity, race, gender, and age. Despite being a flawed measure, BMI is widely used today in the medical community because it is an inexpensive and quick method for analyzing potential health status and outcomes.

What Is Alli Used For?

The Food and Drug Administration (FDA) has approved Alli to aid in weight loss in adults 18 and older who are medically overweight. The drug was first approved in 1999. It is meant to be used along with a reduced-calorie, low-fat diet and regular exercise.

Alli is a short-term weight-loss drug. In clinical trials ranging from six weeks to six months long, this medication was shown to be effective for weight loss in adults, compared to diet alone.

How to Take Alli

Alli comes as a capsule that you take by mouth. You'll take one capsule of Alli with each meal containing fat, up to three times per day.

Keep in mind that Alli works by blocking fat from getting absorbed. If you skip a meal, or if your meal does not contain fat, you can skip that dose.

Be sure to check nutritional labels to learn how much fat is in the foods you are eating. Your meals should contain balanced amounts of protein, carbohydrates, and fat. A good rule of thumb is to aim for a diet that is less than 30% fat. If you take Alli with a very high-fat meal (more than 30% fat content), you are more likely to experience unpleasant side effects.

Alli affects the way your body absorbs fat, and it can also interfere with how your body absorbs certain vitamins. These vitamins are known as fat-soluble vitamins and include vitamins A, D, E, and K.


Store Alli at room temperature in a dry place, away from light and moisture. Do not store in a bathroom. Keep Alli and all medications away from children and pets.

How Long Does Alli Take To Work?

Alli starts blocking your body’s absorption of fat right after you take your first dose. If you take Alli capsules consistently, along with a reduced-calorie, low-fat diet, and regular exercise, you could see results within two weeks. It takes longer for some people, up to six months.

What Are the Side Effects of Alli?

This is not a complete list of side effects, and others may occur. A healthcare provider can advise you on side effects. If you experience other effects, contact your pharmacist or a medical professional. You may report side effects to the FDA at or 800-FDA-1088.

Common Side Effects

Common side effects of Alli include:

  • Gas with oily spotting
  • Loose stools
  • Oily stools
  • More frequent bowel movements that may be hard to control

Note that these side effects may become worse if you take Alli with a high-fat meal.

To minimize the risk of side effects, you should take Alli with a meal containing 30% or less of its calories from fat. If your meal does not contain any fat, you should skip that dose of Alli.

Severe Side Effects

Rarely, Alli may cause severe side effects.

These side effects and their related symptoms may include:

  • Liver problems: Symptoms may include severe abdominal pain or swelling, yellowish skin or eyes, and dark urine.
  • Kidney stones: Symptoms of kidney stones may include back or side abdominal pain, difficulty urinating, and red or pink urine.
  • Allergic reaction or anaphylaxis: Symptoms of anaphylaxis may include rash, hives, swelling around the lips, tongue, and face, and trouble breathing. Seek emergency medical assistance right away if you have these symptoms.

Long-Term Side Effects

Long-term use of orlistat may be associated with vitamin D deficiency, osteoporosis, gallbladder problems, and an increased risk of colon cancer. But, more research is needed to confirm if these safety concerns are valid.

Alli is not meant for long-term use. Consult your healthcare provider if you are not seeing results within a few months of starting Alli.

Report Side Effects

Alli may cause other side effects. Call your healthcare provider if you have any unusual problems while taking this medication. If you experience a serious side effect, you or your provider may send a report to the Food and Drug Administration's (FDA) MedWatch Adverse Event Reporting Program or by phone (800-332-1088).

Dosage: How Much Alli Should I Take?

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The dose of this medicine will be different for different patients. Follow your doctor's orders or the directions on the label. The following information includes only the average doses of this medicine. If your dose is different, do not change it unless your doctor tells you to do so.

The amount of medicine that you take depends on the strength of the medicine. Also, the number of doses you take each day, the time allowed between doses, and the length of time you take the medicine depend on the medical problem for which you are using the medicine.

  • For oral dosage form (capsules):
    • For treatment of obesity:
      • Adults and teenagers—120 milligrams (mg) three times a day with meals containing fat.
      • Children younger than 12 years of age—Use and dose must be determined by your doctor.

Missed Dose

Alli should be taken with a meal containing fat. If you forget to take your dose and it has been less than an hour since your meal, you can still take your dose.

If you skip a meal or eat a nonfat meal, you should also skip your dose of Alli.

Overdose: What Happens If I Take Too Much Alli?

After you take Alli, its active ingredient, orlistat, stays in your digestive tract. This drug does not absorb into your blood to any significant extent. So, an overdose of Alli is not expected to be dangerous.

Still, if you think you or someone else took too much Alli, you should consult a healthcare professional. In some cases, they may recommend that you go to a hospital for treatment or observation.

What Happens If I Overdose on Alli?

If you think you or someone else may have overdosed on Alli, call a healthcare provider or the Poison Control Center (800-222-1222). If someone collapses or isn't breathing after taking Alli, call 911 immediately.


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It is very important that your doctor check your or your child's progress at regular visits, to make sure that this medicine is working properly. Blood and urine tests may be needed to check for unwanted effects.

Using this medicine while you are pregnant can harm your unborn baby. Use an effective form of birth control to keep from getting pregnant. If you think you have become pregnant while using this medicine, tell your doctor right away.

For patients with diabetes: Weight loss may result in an improvement in your condition, and your doctor may need to change your dose of oral diabetes medicine or insulin.

This medicine may cause a serious type of allergic reaction called anaphylaxis. Anaphylaxis can be life-threatening and requires immediate medical attention. Call your doctor right away if you or your child have a rash; itching; hoarseness; trouble breathing; trouble swallowing; or any swelling of your hands, face, or mouth while you are using this medicine.

Stop using this medicine and check with your doctor right away if you or your child have pain or tenderness in the upper stomach; pale stools; dark urine; loss of appetite; nausea; unusual itching; unusual tiredness or weakness; or yellow eyes or skin. These could be symptoms of a serious liver problem.

This medicine may increase your risk of having kidney stones. Check with your doctor right away if you or your child have blood in the urine, nausea and vomiting, pain in the groin or genitals, or sharp back pain just below the ribs.

Weight loss with this medicine may increase your risk of having gallstones. Check with your doctor right away if you or your child have severe stomach pain with nausea and vomiting.

Do not take other medicines unless they have been discussed with your doctor. This includes prescription or nonprescription (over-the-counter [OTC]) medicines and herbal or vitamin supplements.

What Are Reasons I Shouldn’t Take Alli?

You should not take Alli if:

  • You are not overweight.
  • You have been diagnosed with malabsorption (problems absorbing nutrients from food).
  • You are taking cyclosporine.
  • You are pregnant or breastfeeding.

What Other Medications May Interact With Alli?

Alli can interact with certain medications.

Before taking Alli, make sure to give a list of all prescription and OTC medications, including vitamins and supplements, to your healthcare provider for review.

Some medications that may interact with orlistat (the active ingredient in Alli capsules) include:

Before taking Alli, check with your healthcare provider if you are taking the above medications. In some cases, they may need to adjust the dosage of your other medication. Or they may advise you to separate doses of Alli from the other drug by at least four hours.

In other cases, they may advise you not to take Alli because it may cause certain drugs to be less effective.

Alli should not be taken with any other weight loss drug or product.

People taking Alli should take a multivitamin to help prevent vitamin deficiencies. Be sure to take the multivitamin at bedtime or at least two hours apart from orlistat.

What Medications Are Similar?

Below is a list of FDA-approved weight loss drugs that may be considered alternatives to Alli:

  • Adipex-P (phentermine): stimulant drug available as an oral tablet or capsule
  • Contrave (naltrexone and bupropion): combination drug that comes as an oral tablet
  • Qsymia (phentermine and topiramate): combination drug that comes as an oral capsule
  • Saxenda (liraglutide): daily injection, classified as GLP-1 agonist
  • Wegovy (semaglutide): GLP-1 agonist that you inject once weekly.
  • Xenical (orlistat): oral capsule that contains a higher strength of orlistat than Alli

These medications work differently than Alli but are also used to aid in weight loss. While Alli is available OTC, the medications listed above are available by prescription only.

Keep in mind that all weight loss drugs should be used along with a healthy diet and regular exercise.

Talk to your healthcare provider to determine if one of these options is right for you.

Frequently Asked Questions

  • How much should I expect to lose while taking Alli?

    According to Alli's manufacturer, for every 5 pounds, you lose from dieting, Alli can help you lose an extra 2-3 pounds. In clinical trials of orlistat, people lost an average of 5-10 pounds within six months of taking Alli along with a reduced-calorie, low-fat diet.

  • Do the side effects from Alli eventually go away?

    Alli commonly causes digestive side effects that may be unpleasant, such as loose stools, gas with oily spotting, and fecal incontinence (not making it to the bathroom in time). These side effects most often occur in the first one to four weeks of treatment.

    With continued use of Alli, these side effects should become less problematic, especially as you learn to avoid high-fat meals. Taking Alli with a high-fat diet makes the digestive side effects worse.

  • What is the difference between Alli and Xenical?

    Alli and Xenical both contain the same active ingredient: orlistat.

    But, Alli is an OTC capsule and contains 60 milligrams of orlistat. Xenical is available by prescription and contains 120 milligrams of orlistat.

  • How long can I take Alli?

    You can stop taking Alli once you achieve your weight-loss goal. Most weight loss occurs within six months of starting this medicine. After stopping Alli, you should continue to follow a balanced diet and exercise regularly to help maintain a healthy weight.

How Can I Stay Healthy While Taking Alli?

Trying to lose weight can be an overwhelming task. Keep in mind that long-term weight management requires a shift in how you eat and live your life; it is not something that happens overnight.

While taking Alli, it is important to follow a reduced-calorie, low-fat diet. Aim for about 30% or less of your total calories to come from fat. Examples of foods containing fat include oils, fried foods, and red meat. This will help lessen unpleasant side effects that may occur while taking Alli. It will also help the medication work more effectively toward your weight loss goal.

Remember that you are not alone in your efforts to reach a healthy weight. Healthcare professionals can help. Consider involving a friend, partner, or a potential support group to help you stay accountable and to make the journey more fun.

Medical Disclaimer

Verywell Health's drug information is meant for educational purposes only and is not intended to replace medical advice, diagnosis, or treatment from a healthcare provider. Consult your healthcare provider before taking any new medication(s). IBM Watson Micromedex provides some of the drug content, as indicated on the page.

7 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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  2. Food and Drug Administration. Xenical label.

  3. Centers for Disease Control and Prevention. Defining Adults Overweight & Obesity.

  4. Heck AM, Yanovski JA, Calis KA. Orlistat, a new lipase inhibitor for the management of obesityPharmacotherapy. 2000;20(3):270-279. doi:10.1592/phco.

  5. National Library of Medicine. MedlinePlus. Orlistat.

  6. GSK. Frequently Asked Questions About Alli.

  7. Mayer SB, Graybill S, Raffa, SD, et al. Synopsis of the 2020 U.S. VA/DoD clinical practice guideline for the management of adult overweight and obesity. Military Medicine. 2021:186(9-10):884-896. doi:10.1093/milmed/usab114

By Patricia Weiser, PharmD
Patricia Weiser, PharmD, is a licensed pharmacist and freelance medical writer. She has more than 14 years of professional experience.