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Head-to-head evidence comparison — which supplement is right for you?
Orlistat vs Vitamin D3: Vitamin D3 has the stronger overall evidence (7.5 vs 6/10); they're alternatives for metabolic health — the best pick depends on your goals. Take the 60-second quiz for a pick tailored to your goals.
Vitamin D3 wins 3 of 3 categories. Both are solid choices — the best pick depends on your specific goals.
Verdict
Mostly mechanism / observational
Top outcomes
Verdict
Probably helps
7 of 14 studies with measurable effects showed benefit.
Top outcomes
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)
2000-4000 IU daily
Morning with breakfast
D3 (cholecalciferol) softgel or liquid
and 2 more not shown
and 1 more not shown
Lower vitamin D absorption, with measurable falls in fat-soluble vitamin concentrations reported during orlistat treatment.
Orlistat can reduce vitamin D absorption. Ask your prescriber or pharmacist to confirm your vitamin D or multivitamin plan. When taking a vitamin supplement with US Xenical, separate it by at least two hours before or after an orlistat dose. Follow any monitoring advice.
4–12 weeks to onset; maximal by 6–12 months
Year 2 of continuous use
Years
3–12 months
4-8 weeks
4-8 weeks
2-4 weeks
4-8 weeks
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
Vitamin D supplementation vs. placebo and incident type 2 diabetes in an ancillary study of the randomized Vitamin D and Omega-3 Trial
Nature communications (2025) · Rct · n=22220
Ancillary analysis of VITAL: 22,220 adults without T2D randomized to vitamin D3 2000 IU/day or placebo, with a meta-analysis of 3 additional trials.
Vitamin D Supplementation for Patients with Dysmenorrhoea: A Meta-Analysis with Trial Sequential Analysis of Randomised Controlled Trials
Nutrients (2024) · Meta analysis · n=687
TSA revealed that the current RCTs provide sufficient information.
Vitamin D and respiratory tract infections
BMJ (2017) · Meta analysis · n=11321
25 RCTs, 11 321 participants aged 0 to 95 years. Vitamin D reduced acute respiratory tract infection overall (adjusted OR 0.88, 95% CI 0.81 to 0.96).
Both points come from a meta-analysis of double-blind cholecalciferol trials in people aged 60 and over (PMID 15886381). Trials at 700 to 800 IU a day cut hip fracture risk by 26% (RR 0.74) and non-vertebral fractures by 23%, plotted at 800 IU. Trials at 400 IU a day showed no benefit (hip fracture RR 1.15), and the WHI trial of 400 IU with 1,000 mg calcium did not significantly reduce hip fracture (PMID 16481635). Most of these trials also gave calcium, and the Cochrane review found vitamin D alone unlikely to prevent fractures while vitamin D with calcium gave a small reduction (PMID 24729336). Doses above 800 IU were not compared, so no optimal dose or ceiling is set.
AI-estimated from published studies. Interpret as directional guidance.
Vitamin D3 has a higher evidence score (7.5/10 vs 6/10) and wins in 3 of 3 categories.
For metabolic health, Orlistat has a higher relevance score (58 vs 55).
Lower vitamin D absorption, with measurable falls in fat-soluble vitamin concentrations reported during orlistat treatment. Orlistat can reduce vitamin D absorption. Ask your prescriber or pharmacist to confirm your vitamin D or multivitamin plan. When taking a vitamin supplement with US Xenical, separate it by at least two hours before or after an orlistat dose. Follow any monitoring advice. Consult a healthcare provider for personalized advice.
The honest tier list — proven staples vs situational vs mostly marketing. The hub the other guides feed into.
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Berberine, inositol, magnesium vs the cinnamon/chromium hype — and the med-interaction warning.
The right pick depends on your goals. Answer a few quick questions for a personalised recommendation — or dig into the full evidence on each.