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GI Lipase Inhibitors for Weight Loss

Reviewed by: HU Medical Review Board | Last reviewed: June 2023

Obesity is a common health problem, and one factor can be eating too much fat. GI lipase inhibitors are a class of drugs that reduce the body’s absorption of fat that is consumed. This leads to a decrease in calorie intake from fat. For this reason, GI lipase inhibitors are used for obesity treatment. There are prescription and non-prescription forms of these drugs.1-4

How do GI lipase inhibitors work?

These drugs work by targeting pancreatic lipase, an enzyme that breaks down dietary fats in the intestine. By blocking the action of (inhibiting) this enzyme, GI lipase inhibitors prevent the breakdown of dietary fats. This reduces their absorption by the body.1-4

The unabsorbed fat is then passed out of the body through stool, or poop. This results in a decrease in caloric intake from fat, which can help with weight loss.1-4

Examples of GI lipase inhibitors

Orlistat is a GI lipase inhibitor that has been approved by the US Food and Drug Administration (FDA) for obesity treatment. Orlistat comes in capsule form that is taken by mouth. Take Orlistat exactly as directed, and talk with your doctor about any questions or concerns you may have.3-5

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Orlistat is available as both a prescription drug (Xenical®) and an over-the-counter product (Alli®):3,4


Xenical is a prescription drug used to treat obesity in adults. It can also be used as a weight maintenance drug to reduce the risk of weight regain after weight loss.3,5

Xenical is approved for use in adults who have a body mass index (BMI) of:3,5

  • 30 or greater
  • 27 or greater, with at least 1 weight-related condition such as high blood pressure, type 2 diabetes, or dyslipidemia

Xenical is meant to be used alongside a reduced calorie and reduced fat diet, regular exercise, and other behavior changes.4,5

For more information, read the full prescribing information of Xenical.


Alli is an over-the-counter product that is used for adults seeking weight loss. Alli is meant to be used along with a reduced-calorie and low-fat diet as well as an exercise plan.2,3,6

For more information, read the full prescribing information of Alli.

What are the possible side effects?

Side effects can vary depending on the specific drug you are taking. The most common side effects of GI lipase inhibitors are:1-4

  • Gas with oily spotting
  • Oily or fatty stools
  • Loose stools
  • Bathroom urgency and difficulty controlling bowel movements
  • Stomach pain
  • Headaches
  • Anxiety

These are not all the possible side effects of GI lipase inhibitors. Talk to your doctor about what to expect when taking GI lipase inhibitors. You also should call your doctor if you have any changes that concern you when taking a GI lipase inhibitor.

Other things to know

You should aim to eat a nutritious, balanced diet when taking GI lipase inhibitors. About 30 percent of your daily calories should come from healthy fats. Make sure to read food labels closely. Doctors also recommend taking a multivitamin that contains fat-soluble vitamins to make sure you are getting adequate nutrition.5,6

Do not take these drugs if you:5,6

  • Are pregnant, intending to become pregnant, or breastfeeding
  • Have been previously diagnosed with malabsorption problems
  • Are not overweight

Orlistat can interact with certain other drugs, including drugs that are used to prevent transplant rejection. Do not use it if you have had an organ transplant.5,6

Before beginning treatment for obesity, tell your doctor about all your health conditions and any other drugs, vitamins, or supplements you take. This includes over-the-counter drugs.

Talk with your doctor

GI lipase inhibitors should be used for weight loss only under the guidance of a healthcare professional. As medical advancements are made, there may be new developments in the field of GI lipase inhibitors for obesity treatment. Always ask your doctor for the most up-to-date and accurate information on available treatments.