DOSEGUY

Orlistat

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Also seen as: Xenical, Alli

The Dose Guy’s verdict
Sep 1, 2026
3 sources

Orlistat works, barely, and the way it works is the problem. Block a third of the fat you eat from absorbing and the unabsorbed fat has to go somewhere, which is through you, fast, oily, and unpredictable. The weight loss is real but modest, a couple of kilos over placebo across years of data, and it vanishes the moment you stop. In a world where semaglutide and tirzepatide exist, the main use case is the person who wants something over the counter and is willing to let their colon enforce a low-fat diet.

Would I take it?Caution, it works a little and your gut will remind you.

What it is

A lipase inhibitor that works inside the gut, not the bloodstream. Orlistat binds to the enzymes that break down dietary fat in your intestine so that about a third of the fat you eat passes through undigested, so that fat passes through undigested. The undigested fat is the side effect and the mechanism at the same time: eat a fatty meal on orlistat and you will know it within hours.

It has been around for decades. On the current weight-loss shelf, it is legacy. Semaglutide, tirzepatide, and the rest of the GLP-1 family operate on a different plane, killing hunger at the source rather than blocking one macronutrient at the drain. But orlistat does not need a specialist or an injection, and for some people that accessibility is the whole point.

What the research shows

Decades of trial data confirm a modest effect that has not surprised anyone in twenty years:

Year-one mean weight loss was 10.2% with orlistat and 6.1% with placebo. During year two, people who continued orlistat regained half as much as those switched to placebo.Lancet 1998 · 2-year RCT · n=688
Over four years, mean weight loss was 5.8 kg with orlistat versus 3.0 kg with placebo. Diabetes incidence was 6.2% versus 9.0%, a 37.3% risk reduction, driven by the subgroup with impaired glucose tolerance.Diabetes Care 2004 · XENDOS · n=3305
Across adults with type 2 diabetes or high diabetes risk, orlistat produced 2.40 kg greater weight loss than controls, with a 95% CI of 2.08 to 2.72 kg.BJGP Open 2025 · meta-analysis · 22 trials · n=5921

Realistic protocols

The prescription dose is 120 mg three times daily with meals that contain fat. The over-the-counter dose is 60 mg three times daily. Take it during or within an hour of eating. If a meal has no fat, skip the dose, it has nothing to block.

The real protocol advice is dietary: orlistat does not punish you for eating, it punishes you for eating fat. Keep meals under roughly 15 grams of fat per sitting and the GI effects are manageable. Go higher and the consequences are immediate and educational.

Take a daily multivitamin at bedtime, at least two hours after your last orlistat dose. Orlistat blocks fat absorption, and the fat-soluble vitamins A, D, E, and K ride with the fat. Without the supplement, a long run depletes them.

Prescription120 mg 3x/dayWith each fat-containing meal. Skip if the meal is fat-free.
OTC60 mg 3x/daySame timing, lower dose, slightly gentler.
VitaminsmultivitaminAt bedtime, 2+ hours after the last dose. Fat-soluble vitamins need the gap.

Side effects

The GI effects are the drug. Blocking fat absorption means that fat exits unprocessed:

commonOily spotting, fatty stools, fecal urgency, and increased bowel movements. Worse with higher dietary fat intake. This is not a side effect in the usual sense, it is the mechanism.
commonFlatulence with oily discharge. Diet controls the severity: keep meals lean and it is manageable.
monitorFat-soluble vitamin depletion on long runs. A, D, E, and K all ride with dietary fat. Supplement daily.
monitorRare liver injury has been reported. Severe abdominal pain, dark urine, or yellowing skin is a stop-and-check.

Where to buy

All American Aminos–
$1.33 / 60mg vial$0.022/mg
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PCT.zone–
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✓ verified Sep 12
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