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Head-to-head evidence comparison — which supplement is right for you?
Orlistat vs Tirzepatide: Tirzepatide has the stronger overall evidence (7.8 vs 6/10); they're alternatives for manage weight — the best pick depends on your goals. Take the 60-second quiz for a pick tailored to your goals.
Tirzepatide wins 2 of 3 categories. Both are solid choices — the best pick depends on your specific goals.
Verdict
Mostly mechanism / observational
Top outcomes
Verdict
Too few graded studies
Top outcomes
Shared outcomes (2)
Outcomes where both Orlistat and Tirzepatide have evidence — compare verdict strength side-by-side.
Prescription Xenical: 120 mg three times daily (360 mg/day), taken with or up to 1 hour after each main fat-containing meal. Over-the-counter Alli: 60 mg three times daily (180 mg/day). Skip the dose if a meal is missed or contains no fat. Used alongside a reduced-calorie diet in which fat supplies roughly 30% of energy — a higher-fat meal makes the gastrointestinal side effects markedly worse, not the weight loss better.
With meals
Xenical 120 mg capsule three times daily with meals (prescription)
Once-weekly subcutaneous injection, started at 2.5 mg and escalated by 2.5 mg every 4 weeks to a maintenance dose of 5, 10, or 15 mg (per the prescribing physician and approved indication)
Any time of day
Once-weekly subcutaneous injection (Mounjaro / Zepbound)
and 2 more not shown
4–12 weeks to onset; maximal by 6–12 months
Year 2 of continuous use
Years
3–12 months
Weeks to months
Months (dose-escalated over ~20 weeks)
Weeks to months
Mostly during titration
XENical in the prevention of diabetes in obese subjects (XENDOS) study: a randomized study of orlistat as an adjunct to lifestyle changes for the prevention of type 2 diabetes in obese patients.
Diabetes Care (2004) · Rct · n=3305
4-year double-blind trial randomising 3,305 obese patients (BMI ≥30) to lifestyle changes plus orlistat 120 mg or placebo three times daily
Randomised placebo-controlled trial of orlistat for weight loss and prevention of weight regain in obese patients. European Multicentre Orlistat Study Group.
Lancet (1998) · Rct · n=688
743 obese patients (BMI 28–47) entered a 4-week placebo lead-in at 15 European centres; 688 were randomised double-blind to orlistat 120 mg three times a day or placebo for 1 year on a 600 kcal/day-deficit diet, then reassigned for a second 52-week weight-maintenance period
Weight control and risk factor reduction in obese subjects treated for 2 years with orlistat: a randomized controlled trial.
JAMA (1999) · Rct · n=892
2-year randomised, double-blind, placebo-controlled trial at 18 US research centres; 1,187 obese adults (BMI 30–43) entered and 892 were randomised, with 223 placebo- and 657 orlistat-treated subjects in the intent-to-treat analysis
Tirzepatide versus Semaglutide Once Weekly in Patients with Type 2 Diabetes.
N Engl J Med (2021) · Rct · n=1879
Open-label 40-week phase-3 head-to-head RCT (SURPASS-2) in 1879 patients with type 2 diabetes, tirzepatide 5/10/15 mg vs semaglutide 1 mg
Tirzepatide Once Weekly for the Treatment of Obesity.
N Engl J Med (2022) · Rct · n=2539
72-week phase-3 double-blind RCT (SURMOUNT-1) in 2539 adults with obesity (without diabetes), tirzepatide 5/10/15 mg vs placebo
Tirzepatide as Compared with Semaglutide for the Treatment of Obesity.
N Engl J Med (2025) · Rct · n=751
Phase-3b open-label head-to-head RCT (SURMOUNT-5) in 751 adults with obesity but without diabetes, max-tolerated tirzepatide vs max-tolerated semaglutide
Tirzepatide has a higher evidence score (7.8/10 vs 6/10) and wins in 2 of 3 categories.
For manage weight, Tirzepatide has a higher relevance score (90 vs 72).
No documented interaction was found in the data searched. This does not establish that this exact combination is safe.
The right pick depends on your goals. Answer a few quick questions for a personalised recommendation — or dig into the full evidence on each.