Medical Author: Melissa Conrad Stoppler, MD
Medical Editor: William C. Shiel, Jr., MD, FACP, FACR
The U.S. Food and Drug Administration approved orlistat capsules, branded as alli, as an over-the-counter (OTC) treatment for overweight adults in February, 2007. The drug had previously been approved in 1999 as a prescription weight loss aid, whose brand name is Xenical). The OTC preparation will have a lower dosage than prescription Xenical and is produced and sold by GlaxoSmithKline under the name of Alli.
Unlike appetite suppressants, orlistat (Xenical) works as a weight loss aid by acting upon the function of the gastrointestinal tract. The drug binds to an enzyme known as gastrointestinal lipase and inhibits the action of this enzyme, which plays a role in breaking down fats for absorption in the GI tract. As a result, up to 30% of ingested fat is not absorbed by the body.
Orlistat is recommended only for people 18 years of age and over in combination with a diet and exercise regimen. People who have difficulties with the absorption of food or who are not overweight should not take orlistat. Overweight is defined by the U.S. National Institutes of Health as having a body mass index (BMI) of 27 or greater.
Orlistat can be taken up to three times a day, with each fat-containing meal. The drug may be taken during the meal or up to one hour after the meal. If the meal is missed or is very low in fat content, the medications should not be taken. Because of its interference with absorption of fat from the GI tract, the absorption of the fat-soluble vitamins (A, D, E, and K) may also be affected in people taking orlistat. It is recommended that those taking orlistat also take a daily multivitamin supplement containing these vitamins.
The most common side effects of orlistat (Xenical) are changes in bowel habits. These include gas, the urgent need to have a bowel movement, oily bowel movements, oily discharge or spotting with bowel movements, an increased frequency of bowel movements, and the inability to control bowel movements. Women may also notice irregularities in the menstrual cycle while taking orlistat. Side effects are most common in the first few weeks after beginning to take orlistat. In some people the side effects persist for as long as they are taking the drug.
People with diabetes, thyroid conditions, who have received an organ transplant, or who are taking prescription medications that affect blood clotting should check with their physician before using OTC orlistat (Alli), since drug interactions with certain medications are possible.