Orlistat OTC (Alli)
The only FDA-approved over-the-counter weight loss drug. A half-strength version of prescription Xenical (60 mg vs. 120 mg). Works by blocking approximately 25% of dietary fat from being absorbed in the intestine.
Quick read · 3 min
- •Evidence: Strong — backed by large, well-conducted trials
- •In clinical trials of prescription-strength orlistat (120 mg, Xenical), participants lost approximately 2.
- •The main side effects are GI-related: oily or greasy stools, faecal urgency, and potential faecal incontinence — particularly if a high-fat meal is eaten.
- •Unlike prescription drugs, supplements are not tested for effectiveness by the FDA before sale
Based on clinical trials · No rankings · Every claim linked to source
Last reviewed: March 2026
How it works
Blocks pancreatic lipase enzymes in the small intestine, preventing about 25–30% of dietary fat from being broken down and absorbed. The undigested fat passes through the digestive system and is excreted. The GI side effects are directly tied to fat intake — eating a high-fat meal worsens them significantly.
What the evidence shows
In clinical trials of prescription-strength orlistat (120 mg, Xenical), participants lost approximately 2.9 kg more than placebo over one year in a meta-analysis of 17 randomised controlled trials. The 4-year XENDOS trial showed 2.8 kg additional weight loss versus placebo plus lifestyle changes, and a 37% reduction in progression to type 2 diabetes. The OTC dose (60 mg) has less evidence than the prescription strength but uses the same mechanism at half the dose.
Safety
The main side effects are GI-related: oily or greasy stools, faecal urgency, and potential faecal incontinence — particularly if a high-fat meal is eaten. These are not dangerous but can be embarrassing and inconvenient. Orlistat also reduces absorption of fat-soluble vitamins (A, D, E, K) — a multivitamin taken at bedtime (away from doses) is recommended. Rare cases of severe liver injury have been reported, though the link is uncertain.
Community insights
These are personal experiences shared in public online communities — not medical advice.
“The side effects are the mechanism — they 'punish' high-fat eating. Many people accidentally adopt a low-fat diet because they want to avoid the GI consequences.”
“Keep dark clothing and liners on hand for the first few weeks. Most people say the side effects improve once they learn the right fat intake level.”
Common questions
After reading this page, most people compare this with other supplements, look at prescription options, or check what they can do today without a prescription.