FDA approves orlistat (Xenical), the first lipase-inhibitor weight drug

The FDA approved Xenical, brand name for orlistat, on April 23, 1999, making it the first lipase-inhibitor weight-loss drug on the US market ^[1]. The 120 mg prescription capsule was cleared for adults with a body mass index of 30 or greater, or 27 or greater with a weight-related health risk such as high blood pressure, and for adolescents ages 12 and older ^[1][2]. That adolescent approval set it apart from most other weight-loss drugs at the time.

Orlistat works differently from the GLP-1 drugs that dominate the weight-loss conversation today. Instead of acting on appetite signals in the brain, it blocks an enzyme called lipase in the digestive tract. Lipase normally breaks down dietary fat so the body can absorb it. When orlistat blocks that enzyme, about 25% of the fat in a meal passes through the body undigested instead of being absorbed ^[2]. That is why orlistat remains the only FDA-approved weight drug that works entirely in the gut rather than the brain, according to background collected by GoodRx ^[1].

In 2007, the FDA approved a lower-dose, over-the-counter version called Alli, sold at 60 mg per capsule, half the strength of prescription Xenical ^[1][2]. Studies cited by GoodRx suggest the 60 mg dose delivers about 85% of the effectiveness of the 120 mg dose ^[1]. Alli is approved for adults 18 and older with a BMI of 25 or more, a lower bar than Xenical's prescription-only threshold of 30, or 27 with risk factors ^[2]. Alli has not been studied for safety and effectiveness in adolescents, so it is approved for adults only ^[1].

Weight loss with orlistat tends to be modest. Mayo Clinic notes that in some studies, more than 40% of people taking Alli alongside a reduced-calorie diet and increased physical activity lost 5% or more of their body weight within a year, and people who dieted, exercised, and took Alli lost an average of 5.7 pounds more over a year than those who only dieted and exercised ^[2]. A 5% weight loss is generally considered clinically meaningful because it can start lowering the risk of heart disease and diabetes ^[2].

Why it matters for patients

Orlistat's mechanism means its side effects are almost entirely digestive: oily or loose stools, gas with oily discharge, more frequent and sometimes urgent bowel movements, and stomach upset, especially after high-fat meals ^[2]. Because it blocks fat absorption, it can also reduce absorption of fat-soluble vitamins A, D, E, and K, so people taking it are advised to time a multivitamin away from doses ^[2]. In 2010 the FDA reviewed rare reports of serious liver injury linked to orlistat but found no evidence confirming the drug caused the injuries, though product labels were updated as a precaution ^[2].

For patients weighing options today, orlistat sits apart from newer GLP-1 medications like semaglutide (Ozempic, Wegovy, Rybelsus) and tirzepatide (Mounjaro, Zepbound), which act on brain and gut hormone pathways and have shown larger average weight loss in trials. Orlistat's gut-only mechanism, oral pill form, and over-the-counter availability as Alli make it a distinct, lower-cost option, though the sources describe its expected weight loss as modest compared with diet and exercise alone ^[2].

What happens next

The sources do not describe any pending regulatory changes to orlistat's approval status. Xenical remains available by prescription, including as a lower-cost authorized generic, while Alli remains available over the counter ^[1].