Alli (Orlistat) Review: The FDA-Approved OTC Weight-Loss Pill

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Alli (orlistat 60 mg) is, as of this writing, the only weight-loss pill the FDA has approved for over-the-counter sale in the United States. It works by blocking your gut from absorbing some of the fat you eat, and in a one-year placebo-controlled trial it produced about 8.5% loss of starting body weight versus 5.4% on placebo. It is real, FDA-reviewed, and modest — not a fat-burner and not a GLP-1. Expect single-digit percentage weight loss when paired with a reduced-calorie, lower-fat diet, plus well-documented digestive side effects if you eat fatty meals. This review explains how Alli works, what the evidence actually shows, the honest side-effect picture, who it fits, and how it compares to supplements and prescription options.

What is Alli and why is its FDA status notable?

Alli is the 60 mg over-the-counter version of orlistat, a lipase inhibitor. It is the only nonprescription weight-loss drug the FDA has approved — every other OTC "diet pill" on shelves is a dietary supplement, which the FDA does not review for safety or effectiveness before sale.

The FDA approved the 60 mg OTC dose (Alli) in 2007; the 120 mg prescription version (Xenical, NDA #021887) was first approved in 1999, per [FDA labeling records](www.accessdata.fda.gov/drugsatfda_docs/nda/2007/021887s000_MedR_P2.pdf). That regulatory review is the single most important thing separating Alli from the supplement aisle.

This matters because most products marketed for weight loss are supplements with limited or insufficient evidence. If you want the difference spelled out, see our guide to [OTC vs prescription weight-loss options](/otc-vs-prescription-weight-loss). Alli is the rare bridge: bought without a prescription, but reviewed like a drug.

How does orlistat work?

Orlistat blocks fat digestion in your gut. It does not suppress appetite, raise metabolism, or "burn" anything — it simply stops some dietary fat from being absorbed, so those calories pass out of the body instead.

Mechanically, orlistat reversibly inhibits gastric and pancreatic lipases, the enzymes that break triglycerides into absorbable fatty acids. According to [StatPearls (NCBI Bookshelf)](www.ncbi.nlm.nih.gov/books/NBK542202), at the 120 mg prescription dose it reduces dietary fat absorption by about 30%. The OTC 60 mg dose blocks somewhat less.

A key consequence: orlistat only works on the fat you eat. Take it with a fat-free meal and it does little; take it with a greasy meal and you get both more blocked fat and more side effects. It acts locally in the gut and is minimally absorbed into the bloodstream.

How much weight can you realistically lose on Alli?

Modest amounts. In trials, orlistat plus a reduced-calorie diet produced roughly 5–10% loss of starting body weight over a year — only a few percentage points more than diet and placebo alone.

The most-cited evidence: in a one-year randomized, placebo-controlled trial, orlistat-treated patients lost an average of 8.5% of initial body weight versus 5.4% for placebo, and a larger share reached at least 10% loss ([PubMed-indexed RCT](pubmed.ncbi.nlm.nih.gov/10599349)). Trials of the lower OTC dose likewise found it produces modest weight loss above diet alone.

[Mayo Clinic](www.mayoclinic.org/healthy-lifestyle/weight-loss/in-depth/alli/art-20047908) frames it plainly: Alli can help you lose somewhat more weight than diet and exercise alone, but the difference is small and only holds if you keep up the lifestyle changes. The honest takeaway: Alli is a helper, not a solution. Most of the work is still diet and activity.

What are the side effects of Alli?

The side effects are mostly gastrointestinal and directly tied to how it works: unabsorbed fat has to go somewhere. Common effects include oily stools, oily spotting, gas with discharge, urgent bowel movements, and more frequent, loose stools.

Per [StatPearls (NCBI Bookshelf)](www.ncbi.nlm.nih.gov/books/NBK542202), these effects stem from the drug's local action blocking fat digestion — and they tend to worsen the more fat you eat. They are, in effect, built-in feedback: a high-fat meal often produces uncomfortable results, which is partly why the diet change is unavoidable.

Two things to manage carefully:

• Fat-soluble vitamins. Because orlistat reduces absorption of vitamins A, D, E, and K, the FDA label recommends taking a daily multivitamin containing these (and beta-carotene) at bedtime, at least two hours apart from a dose of orlistat.
• Rare serious liver injury. Orlistat labeling notes rare reports of severe liver injury. These are uncommon, but stop use and seek care for symptoms like itching, dark urine, jaundice, or loss of appetite, per [orlistat DailyMed labeling](dailymed.nlm.nih.gov/dailymed/lookup.cfm?setid=f81dfaeb-46d5-47ce-9ef6-19259f5ac61c).

Does Alli interact with medications?

Yes — several interactions are clinically important, which is why a clinician check-in matters before starting. Because orlistat changes fat absorption, it can affect how some drugs are absorbed.

Orlistat labeling flags these specifically:

• Cyclosporine: levels can drop; the drugs should not be taken at the same time (separate by at least 3 hours).
• Levothyroxine: thyroid function should be monitored; separate dosing is advised.
• Warfarin: monitor coagulation closely, as orlistat can alter vitamin K status.

These are drawn from [FDA-approved orlistat labeling](dailymed.nlm.nih.gov/dailymed/lookup.cfm?setid=f81dfaeb-46d5-47ce-9ef6-19259f5ac61c). If you take any prescription medication — or have gallbladder, kidney, thyroid, or malabsorption conditions — confirm with a licensed clinician that Alli is appropriate for you.

Who should consider Alli — and who should not?

Alli may suit motivated adults with overweight or obesity who already plan to follow a reduced-calorie, lower-fat diet and want a modest, FDA-reviewed option they can buy without a prescription. The label is intended for adults 18 and older with a BMI of 25 or higher.

It is a reasonable fit if you:

• Want an OTC option with real regulatory review rather than an unvetted supplement.
• Can commit to a lower-fat diet (which both improves results and limits side effects).
• Prefer a non-systemic drug that mostly acts in the gut.

It is likely a poor fit if you:

• Eat a high-fat diet you don't intend to change (side effects will dominate).
• Are pregnant or breastfeeding, have chronic malabsorption or gallbladder problems, or take interacting medications.
• Expect dramatic results — the average added benefit is a few percentage points.

For a broader view of evidence-graded options across the category, see our roundup of the [best weight-loss supplements](/best-weight-loss), where we rate products by strength of evidence rather than marketing.

Alli vs supplements vs GLP-1 medications

Alli sits between unproven supplements and far more powerful prescription drugs. It is more evidence-backed than typical supplements but produces much smaller weight loss than GLP-1 medications.

Here is the honest hierarchy of effect, with sources:

• Most weight-loss supplements: small or insufficient evidence. The NIH Office of Dietary Supplements notes the data are weak or inconsistent for most ingredients marketed for weight loss ([NIH ODS fact sheet](ods.od.nih.gov/factsheets/WeightLoss-Consumer)). We cover this gap in [supplements vs GLP-1](/supplements-vs-glp1).
• Alli (orlistat 60 mg): roughly single-digit percentage loss of body weight over months when combined with diet — modest but FDA-reviewed, per the trials above.
• GLP-1 medications: much larger. In the STEP 1 trial, semaglutide 2.4 mg produced a mean ~14.9% body-weight reduction over 68 weeks ([Wilding et al., NEJM 2021](www.nejm.org/doi/full/10.1056/NEJMoa2032183)), and in SURMOUNT-1, tirzepatide reached ~20.9% at the 15 mg dose ([Jastreboff et al., NEJM 2022](www.nejm.org/doi/full/10.1056/NEJMoa2206038)).

So the trade-offs are clear. Supplements are easy to buy but mostly under-evidenced. GLP-1s are dramatically more effective but require a prescription, cost more, and carry their own side-effect profile. Alli is the middle path: real evidence, no prescription, modest results, and digestive side effects you largely control through diet.

The bottom line on Alli

Alli is legitimate. It is the only FDA-approved OTC weight-loss pill as of this writing, its mechanism is well understood, and its modest benefit is supported by real clinical trials rather than testimonials. But "modest" is the operative word — expect single-digit percentage loss, not transformation, and only if you change how you eat.

If you want a non-prescription option with genuine regulatory backing and you can commit to a lower-fat diet, Alli is a reasonable, honest choice. If you need substantially more weight loss, the evidence points toward prescription GLP-1 therapy discussed with a clinician. Either way, talk to a licensed healthcare provider before starting, especially if you take other medications.

*This article is for general education and is not medical advice. Decisions about weight-loss medications should be made with a licensed clinician who knows your health history.*