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Alli Weight Loss Aid Review: Safety, Effectiveness, Pros and Cons

Written by Emily Hirsch, MS, RD

Published on March 19, 2021

Our Expert Rating:


About This Rating
The average rating of this product is calculated based on the evaluation of the following factors:
  • Support for Claims:2.0
  • Ingredient Safety:2.0
  • Value for the Price:2.0
  • Brand Transparency:2.0

Alli is the first FDA-approved weight loss pill. While some studies report that it may help with short-term weight loss, the side effects are unpleasant and the long-term effects aren’t yet established.

Alli Weight Loss Aid Review: Safety, Effectiveness, Pros and Cons


  • May help with short term weight loss
  • Can be easily purchased through various retailers
  • FDA Approved


  • Unpleasant side effects
  • Won’t promote long term weight loss
  • Weight loss may be very slow

What Is Alli?

Alli is an over-the-counter weight loss pill that was approved by the FDA in 1999.

The product is intended for obesity management and is meant to be used alongside a low-fat, calorie-restricted diet.

Alli contains orlistat, a type of drug known as a lipase inhibitor. Lipase inhibitors block the body from absorbing dietary fat by blocking an enzyme called lipase.

Lipase helps the body break down and digest the fat we eat. Without lipase, dietary fat bypasses digestion and is expelled from the body.

Dietary fat contains the highest concentration of calories when compared to the other macronutrients, carbs, and protein.

Only one gram of fat has more than double the calories of the identical amount of protein or carbohydrate.

By inhibiting dietary fat absorption, Alli can reduce your calorie digestion which can lead to weight loss.

In clinical trials, Alli has been shown to reduce the absorption of dietary fat by approximately 25%.

The prescription-only version of Alli is called Xenica, which contains 120 mg of orlistat, while Alli, the over-the-counter version contains only 60mg of orlistat.

Alli is manufactured by GlaxoSmithKline. GlaxoSmithKline is a pharmaceutical company that specializes in the development and manufacturing of pharmaceutical products, vaccines, over-the-counter medicines, and health-related consumer products around the globe.

An Evaluation of Orlistat

Alli may help with short-term modest weight loss, but there is very little evidence to suggest that taking Alli will help with long-term weight loss.

In fact, much of the research shows that participants generally gained much of their weight back after a few years.

One of the largest studies on Orlistat was known as the XENDOS study and was conducted in Sweden in 2004.

The study included 3,305 overweight individuals and lasted for 4 years.

In the XENDOS study, researchers divided participants into 2 groups: one took 120 mg of orlistat 3 times a day, while the other group took a placebo.

Both groups ate 800 fewer calories a day and limited their dietary fat to 30% of their total calories.

During the first year of the study, the average weight loss in the orlistat-treated group was 23.3 pounds, while the placebo group lost 13.6 pounds.

However, over the remaining 3 years, there was significant weight regain in both groups.

A 2014 review of the research found that taking orlistat resulted in a 7.5-pound weight loss greater than placebo over 12-months.

This equates to only 3.1% of the initial weight. Researchers also found that after the initial year of treatment, participants slowly regained back much of their weight.

Another 2015 study followed roughly 100,000 people taking orlistat over three years.

Researchers found that while participants did experience modest weight loss, they did not maintain that weight loss long term.

One 2017 study compared the weight loss effectiveness of 60 mg of orlistat to polyglucosamine, a different type of fat inhibitor.

Researchers found that the use of polyglucosamine reduced body weight, body mass index (BMI), and waist circumference more efficiently than orlistat.

Verdict on Claimed Benefits

Below is our summary of the available evidence for the claimed benefits of Alli Weight Loss Aid based on the available research:

  • Assists with weight managementModerate Evidence
  • Can lose 10–15% of your belly fatNo Evidence

Side Effects, Safety, and Dosage

The manufacturers of Alli suggest taking one 60 mg pill within an hour of a fat-containing meal up to three times a day.

When taking Alli, a person’s daily fat intake should be spread over their three main meals which should be no more than 30 percent of total calories.

Alli recommends a fat intake of about 15 grams per meal.

Orlistat can wreak havoc on your gastrointestinal system. Orlistat’s gastrointestinal side effects are related to the undigested fat that will pass through the digestive system.

Furthermore, if you exceed the recommended fat intake, the side effects often become more severe. Side effects include:

  • Anal oily discharge
  • Gas and bloating
  • Oily stools
  • Abdominal pain
  • Rectal discomfort
  • More-frequent bowel movements
  • Urgent or hard-to-control bowel movements
  • Diarrhea
  • Irregular menstrual periods

More serious side effects may include:

  • Hives
  • Itchy rash
  • Difficulty breathing or swallowing
  • Nausea and/or vomiting
  • Yellowing of the skin or eyes
  • Dark-colored urine

You should not take Alli if you have any of the following conditions:

  • Diabetes
  • Thyroid disease
  • Cardiovascular disease
  • Eating disorder
  • Gallbladder disease
  • Kidney stones
  • Pancreatitis
  • Irritable bowel syndrome
  • Malabsorption syndrome
  • Have had an organ transplant
  • Have problems absorbing food
  • Are pregnant or breast-feeding

It is recommended that you only take Alli if:

  • You have a BMI of at least 25.
  • You can adhere to a healthy diet and exercise plan.
  • You do not eat more than 30% fat in each meal.

One 2012 study found that Alli may contribute to liver and kidney damage.

Researchers also found that taking orlistat may increase the effects of aspirin, which may lead to increased bleeding.

Meanwhile, food and nutrient absorption can be affected by taking Alli. Taking orlistat can block your body's absorption of vitamins A, D, E, K, and beta carotene.

Therefore, the FDA recommends that users take a multivitamin while taking the product.

Cost and Where to Buy

A 120-pill pack of Alli cost ranges from $64.99 to $71.99 for a 2-month supply and can be purchased through major retailers like Target, Walgreens, and Rite Aid.

Compared to other weight loss pills, Alli is reasonably priced at between $32 and $36 per month.

Comparison to Alternatives

There are a variety of weight loss pills on the market, most of which have very limited scientific evidence to back up their claims.

Alli is the only lipase inhibitor, or fat blocker, that is available without a prescription.

Glucomannan is a different type of weight loss supplement that uses fiber. It can work by absorbing water in the gut, which takes up space in the stomach.

This can promote a feeling of fullness and help to reduce overall food intake.

Glucomannan supplements can be purchased through Amazon. A month’s supply is between $10–$13, which is less than Alli.

Moreover, Glucomannan may cause some gastrointestinal symptoms but won’t likely be as severe as the symptoms related to Alli.

The Bottom Line

There is no shortage of miracle weight loss pills, supplements, or beverages to choose from.

Unfortunately, many of the health claims made by these products aren’t backed by solid scientific research.

Alli may help prompt your weight loss journey but it will likely be ineffective for long-term success.

Additionally, Alli poses some serious health risks, not to mention the potentially embarrassing side effects.

If your weight loss pill requires you to wear dark pants or bring a change of clothes with you when leaving the house, it may be time to reevaluate your weight loss journey.

It’s also important to note that the pill is only effective if you follow a low-fat, healthy diet and exercise regularly.

These same behaviors will likely help you lose weight without taking a pill like Alli.

A Word from Our RD

Instead of taking Alli, or any other weight loss pill, your weight loss journey can begin by writing down 2-3, small, obtainable goals.

According to research, setting goals can increase the likelihood of achieving significant weight loss.

Examples of goals to help with weight loss may include:

  • Including a lean protein source in all of your meals and snacks.
  • Begin an exercise regime starting out at 30 minutes 3 times per week.
  • Include a fruit and/or vegetable at every meal and snack.
  • Aim for at least 7 hours of sleep per night.
  • Increase your fiber intake by eating whole grains like quinoa, brown rice, and lentil whole grain pasta.
  • Trying to drink water before all of your meals and snacks.
  • Practice mindfulness when eating by ditching all screens and other distractions when enjoying a meal or snack.
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