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Alli Review: Can an OTC Pill Shed Pounds?

Alli Review: Can an OTC Pill Shed Pounds?

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Read our Editorial Guidelines to learn more about what makes our site the premier resource for online health information.

Read our Editorial Guidelines to learn more about what makes our site the premier resource for online health information.

Disclaimer: None of the information in this article constitutes medical advice, and is just the opinion of the writer(s) and published for informational purposes only. We recommend that patients follow their doctor’s guidance in regard to prescription medication.

Alli is a weight loss pill that’s approved by the Food and Drug Administration (FDA) in the U.S. It’s branded as the only over-the-counter (OTC) weight loss medication, because it doesn’t require a prescription from a doctor. The generic name for Alli is orlistat, and we will use these terms interchangeably throughout this article as they refer to the same active ingredient.

In this article we’ll review the medical research on Alli to determine if it’s safe and effective. We’ll explain the side effects of the drug, and highlight some natural alternatives which may be better weight loss options.

Does Alli Work?

The active ingredient in Alli has been studied in many medical trials.

One clinical trial examined whether Alli could lead to weight loss in U.S. soldiers. Over 6 months of treatment, the soldiers lost 1.3 kilograms (kg) of fat mass which is equivalent to 2.87 pounds (lbs). The soldiers weren’t obese, but they were slightly overweight (greater than 2% above the percent body fat standard). 

While this trial did prove that Alli caused weight loss to a statistically significant degree, we don’t find the results very impressive. Less than 0.5 lb fat loss per month is not worth pharmaceutical medication side effects in our opinion.

A separate medical study on Alli had more impressive results. This study had a population of overweight and obese patients who took Alli for 24 weeks. The patients taking Alli lost 15.7% of visceral fat (fat around organs) compared to visceral fat loss of 9.4% on patients taking placebo.

Those taking Alli lost 10.25 pounds of fat overall, which is significant.

Alli has also been proven effective for patients who are only slightly overweight. A clinical trial published in the Annals of Pharmacotherapy journal tested the effects of Alli taken over 16 weeks in patients who were categorized as “mildly to moderately overweight.”

Patients in this trial were put on a restricted calorie diet and took either Alli or a placebo pill. Both groups lost weight, but the group taking Alli lost 2.54 lb more, which equates to an annual weight loss of 8.26 lb.

We can conclude from the available research that Alli is effective for weight loss in patients who are slightly overweight, moderately overweight and obese, as it has been proven to work in all categories of obesity.

How Does Alli Work?

It’s important for patients to know how their drugs function in the body.

Alli weight loss pills work by inhibiting production of certain proteins that break down fat consumed in the diet, as documented by StatPearls which is a leading database of pharmaceutical medications.

Patients taking Alli excrete more fat than they would otherwise, and the above-linked review reports that around 30% less dietary fat is absorbed on Alli than would be otherwise.

These effects are reversible, and when a patient stops taking Alli the pancreatic and gastric proteins function as normal.

Alli Side Effects

Most side effects of Alli are relatively minor and gastrointestinal in nature, but there is a small risk of severe side effects.

The most common side effect as reported by the previously-linked StatPearls database is oily stool (medical term “steatorrhea”), but this should be expected because the way Alli works is by increasing the excretion rate of dietary fats.

A medical review of Alli noted that patients who kept dietary fat intake under 60 grams (g) daily experienced fewer GI-related side effects.

The same resources documents that there is a rare risk of acute kidney injury because Alli can increase oxalate production, which is deposited in the kidneys.

The FDA has also reported that Alli use is associated with a small but increased risk of severe liver injury. Only 13 out of over 40 million patients experienced this side effect.

Should I Take Alli Generic?

The generic form of Alli is called orlistat. Both of these drugs have the exact same active ingredient.

We recommend taking the generic form of drugs because they’re just as effective as brand-name drugs but cheaper.

A medical review published in the PLOS Medicine journal compared the efficacy of generic and branded drugs, and found that there was no difference: “use of generics was associated with comparable clinical outcomes to use of brand-name products.”

Doctors often prescribe brand-name versions because they spoke with representatives from the pharmaceutical company backing the branded drug, and may not be as familiar with generic versions, so we recommend that patients speak with their doctor about the generic alternative to all prescription medications.

Natural Alternatives

Regular caffeine intake has been associated in studies with reduced weight. A meta-study on caffeine and weight loss analyzed results from 13 individual medical trials and found that for every doubling in caffeine intake, weight loss increased. The average weight loss documented in the trial was around 4.41 lbs over 4 weeks.

Caffeine intake isn’t safe for all patients, and should be avoided by patients with high blood pressure, so we recommend that patients speak with their doctor prior to taking caffeine for weight loss.

Drinking black coffee is a healthier and safer option for caffeine intake than caffeine pills. Coffee consumption has been associated with reduced all-cause and cancer mortality in medical research.

Caffeine is effective as a weight loss aid because it’s a mild stimulant which increases base metabolic rate and decreases appetite. We recommend drinking black coffee in the morning so it doesn’t interfere with sleep.

Increased dietary fiber consumption is also proven to cause weight loss, and this is the most well-studied natural weight loss option in our opinion. Increasing dietary fiber intake delays gastric emptying and increases the sense of fullness, which allows for calorie restriction without the cravings.

The Journal of Nutrition published an extensive review documenting how fiber intake predicts weight loss in adults. The vast majority of American adults don’t get enough fiber daily.

The average fiber intake in the study was 25.2 g per day. This can be achieved by eating high-fiber foods like raw vegetables, or by supplementation with fiber powder that contains no filler ingredients like added sugar.

Stay up-to-date on our research reviews


Alli can cause weight loss in overweight patients, but it may come with a host of unpleasant side effects. It’s ultimately up to the patient and their doctor to decide whether pharmaceutical pills are the best weight loss approach.

We tend to recommend lifestyle modifications for weight loss like increased fiber intake and increased caffeine intake (in patients without cardiovascular risk), because these options are cheaper and free of side effects.

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