Orlistat
Also known as: Xenical, Alli, tetrahydrolipstatin, lipase inhibitor
Effective Dosage
120 mg three times daily (prescription); 60 mg three times daily (OTC)
What the Science Says
Orlistat is a prescription (and lower-dose OTC) medication that works by blocking pancreatic and intestinal lipases — the enzymes your gut uses to digest dietary fat. By inhibiting these enzymes, it prevents roughly 30% of the fat you eat from being absorbed, causing it to pass out in your stool instead. Clinical guidance from major obesity societies supports its use at 120 mg three times daily for weight loss, weight maintenance, and reducing risk of type 2 diabetes in people with overweight or obesity (BMI ≥27 with complications, or BMI ≥30). Studies also suggest it may reduce gestational diabetes risk in overweight women with PCOS when used before conception.
What It Doesn't Do
Won't work without dietary changes — it only blocks fat, not carbs or calories from other sources. Not a substitute for lifestyle changes like diet and exercise. Doesn't match the weight loss seen with newer GLP-1 drugs like semaglutide or tirzepatide. Won't prevent alcohol use disorder after bariatric surgery — that benefit belongs to incretin-based therapies. Not a cure for obesity on its own.
Evidence-Based Benefits
Orlistat is a weight-loss medication that works by inhibiting the absorption of dietary fats in the intestines. Clinical trials have shown that it can lead to significant weight loss when combined with a reduced-calorie diet and exercise.
Strong EvidenceEffective at: 60-120 mg daily
Source: auto-research
Absorption & Bioavailability
Poor systemic absorption — intentional by design. Orlistat acts locally in the gut. Peak plasma concentrations remain below 5 ng/mL. Minimal systemic exposure confirmed across both conventional and modified-release formulations.
Red Flags to Watch For
- Causes oily, loose stools, fecal urgency, and oily spotting — especially if you eat high-fat meals; these GI side effects are common and can be socially disruptive
- Only a conditional recommendation from major obesity societies — newer medications like semaglutide and tirzepatide carry stronger evidence ratings
- Blocks absorption of fat-soluble vitamins (A, D, E, K) — supplementation is typically required
- Not appropriate during pregnancy; the PCOS study used it only in the preconception period
- OTC (Alli) dose is half the prescription dose — effectiveness is lower at 60 mg
Products Containing Orlistat
See how Orlistat is used in these analyzed products:
Research Sources
- PubMed
This information is for educational purposes only and is not medical advice. Always consult a healthcare professional before starting any supplement regimen. Last updated: 2026-04-06