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There are a number of reasons why a person may want to lose weight, including reducing disease risk factors, improving overall quality of life, and managing disease-related symptoms.

Even though weight loss can improve health, it’s not always easy to lose excess body fat and maintain that weight loss over time.

Restricting calories leads to compensatory changes in the body, including increased appetite and reductions in energy expenditure, which make weight loss difficult to maintain (1).

This causes many people to seek alternative methods to promote weight loss, including medications and supplements.

Alli is one such product. It’s an over-the-counter (OTC) diet pill that’s actually a low dose pharmaceutical drug.

This drug limits the amount of dietary fat your body absorbs, which reduces calorie intake and may lead to weight loss.

This is a detailed review of Alli diet pills: what they are, how they work, and whether they are right for you.

What is Alli (Orlistat)?

Alli is the OTC version of a pharmaceutical weight loss drug called orlistat (Xenical) (2).

Xenical is a prescription-only medication that contains a higher dose of orlistat than Alli. Alli diet pills contain 60 mg of orlistat, while Xenical pills contain 120 mg (3).

The Food and Drug Administration (FDA) first approved this drug in 1999 as a weight loss aid in people with obesity — a body mass index (BMI) over 30 — and people with overweight — a BMI over 27 — who also have risk factors like high blood pressure, diabetes, or high blood lipid levels.

It’s usually prescribed for long-term obesity management alongside a low fat, calorie-restricted diet (3).

Alli is the OTC version of orlistat, a pharmaceutical drug used in weight management. The prescription-only version contains 120 mg of orlistat, while Alli contains 60 mg.

Pros and cons at a glance

Pros

• When combined with a low calorie, low fat diet and an exercise routine, taking Alli may help you lose slightly more weight than diet and exercise alone.

Cons

• Alli could lead to side effects such as digestive upset, fecal incontinence, and deficiencies in fat-soluble vitamins.
• Alli is not appropriate or safe or everyone and may interact with commonly prescribed medications.

How does Alli work and how do you use it?

Alli works by preventing your body from absorbing dietary fat.

Specifically, it inhibits enzymes called pancreatic and gastric lipases, which are involved in the digestion of fat (2).

These lipases are essential to the digestion of the fats you eat. They help break down fats into free fatty acids that your body can absorb.

Without the action of these enzymes, dietary fat bypasses digestion and is then expelled from your body.

As a lipase inhibitor, Alli has been shown to reduce the absorption of dietary fat by about 30% (2).

Because dietary fat is high in calories, this leads to fewer calories being processed by your body, which can lead to weight loss.

Recommended use

It’s recommended that prescription-only orlistat (120 mg) be taken three times a day, during or within 1 hour after a fat-containing meal (2).

Typically, significant weight loss occurs only after the medication is taken for at least 2 months, though weight loss can begin in as little as 2 weeks.

Alli, which contains 60 mg of orlistat, is recommended to be taken in the same way as the prescription-only medication, 1 capsule with each meal containing fat, for a total of 3 pills per day. You should not take more than 3 Alli pills per day.

The Alli website claims that users can lose a significant amount of belly fat within 12 weeks of use and that, after 24 weeks of use, Alli can help users lose more than 2 inches (5.08 cm) from their waists.

Personalized tools

Along with selling the medication, the Alli website offers resources for Alli users, including recipes, a meal planner and tracker, dining-out guides, a fitness tracker, a weight tracker, workout videos, and more.

After purchasing Alli supplements from the website or in stores such as Costco, customers can create an account on the MyAlli website to gain access to the tools listed above.

The site currently offers hundreds of recipes, integrated shopping lists, and meal ideas for dining out.

Alli interrupts digestion of dietary fats and blocks about 30% of fat from being absorbed. This leads to a reduction in calorie intake. Users can create an account on the MyAlli website to access resources such as recipes and workout videos.

Alli may help you lose small amounts of weight

Several human studies have been conducted on orlistat, the active compound in Alli diet pills.

The most well known is the Swedish XENDOS study, which was published in 2004. It included 3,305 people with obesity and lasted for 4 years (4).

There were two groups in the study. One took 120 mg of orlistat three times daily, while the other group took a placebo.

All participants were instructed to eat 800 fewer calories per day than needed to maintain their current weight and to limit dietary fat to 30% of calories. They were also encouraged to go for walks every day.

Keep in mind that an 800-calorie deficit is significant and not typically recommended to promote safe, sustainable weight loss.

During the first year, the average weight loss in the orlistat-treated group was 23.3 pounds (10.6 kg), while the placebo group lost only 13.6 pounds (6.2 kg).

There was significant weight regain in both groups over the remaining 3 years. Orlistat-treated patients ended up having lost 12.8 pounds (5.8 kg), compared to 6.6 pounds (3.0 kg) in those receiving a placebo.

According to this study, orlistat combined with diet and exercise may make you lose almost twice as much weight as significantly cutting calories and exercise alone.

More studies

According to a research review, the average 12-month weight loss for adults taking orlistat while participating in behavioral weight control programs and following a low fat diet is about 7.5 pounds (3.4 kg) greater than placebo (5).

This amounts to 3.1% of initial weight, which is not particularly impressive. Orlistat 60 mg (the Alli dose) specifically showed an even smaller average weight loss of 5.5 pounds (2.5 kg) compared to the placebo group.

For both doses of orlistat, it also appears that weight is slowly regained after the initial year of treatment.

Additionally, orlistat-induced weight loss may help improve blood pressure, blood sugar, and blood lipid levels and may help reduce the risk of developing diabetes (4, 6, 7).

However, it’s important to know that weight loss — regardless of whether it’s achieved through lifestyle changes alone or with the addition of orlistat — can help reduce these risk factors and prevent chronic disease onset.

Alli is a mildly effective anti-obesity drug, with the average weight loss at 12 months being 5.5 pounds (2.5 kg) greater than placebo.

Do Alli diet pills have any other health benefits?

Alli has also been linked to several other health benefits due to its effect on weight loss, including:

• Reduced type 2 diabetes risk. In the XENDOS study, 4-year use of orlistat reduced the risk of developing type 2 diabetes by 37% (4).
• Reduced blood pressure. A 2020 review of 27 randomized controlled trials found that weight loss induced by orlistat was associated with reductions in blood pressure in people considered overweight or obese (8).
• Reduced LDL (“bad”) and total cholesterol. A 2017 review of 33 trials found that orlistat slightly reduced cholesterol and triglyceride levels, but the reductions were more consistent in people who lost more weight and took orlistat for a shorter time (9).

Prolonged use of Alli may reduce the risk of type 2 diabetes and decrease heart disease risk factors such as high blood pressure and high blood lipid levels.

Potential side effects of Alli

Alli diet pills do have well-documented side effects, some of which are quite unpleasant (2).

Some of the most common side effects of Alli are:

• Digestive symptoms. Because the pills block fat absorption, the presence of undigested fat in the bowel can cause digestive symptoms such as abdominal pain, diarrhea, and flatulence. Some people also experience fecal incontinence and loose, oily stools (2).
• Impaired nutrient absorption. Continued use of Alli can impair the absorption of fat-soluble nutrients such as vitamins A, D, E, and K, leading to nutrient deficiencies. It can also decrease calcium absorption. Taking a multivitamin is recommended. However, a multivitamin should be taken at least 2 hours before or after taking Alli or Xenical (2).
• Increased risk of kidney injury. Alli could increase the risk of kidney issues because the unabsorbed fat binds with calcium in the digestive system. This can cause calcium oxalate crystal deposits to develop in the kidneys, leading to kidney injury (2, 10).
• Drug interactions. Alli may also interfere with the absorption of some medications, including drugs used to treat conditions such as epilepsy, thyroid conditions, irregular heartbeat, and HIV. If you’re taking any medications, it’s important to consult your doctor before taking Alli (2).

Other potential health concerns

In addition to the side effects listed above, there are a few more potential risks to keep in mind if you’re interested in taking Alli.

According to the FDA, 1 U.S. case of liver injury involving the use of Alli and 12 foreign cases of liver injury involving the use of Xenical were reported between April 1999 and August 2009. To put this into perspective, around 40 million people worldwide have used Alli or Xenical (11).

However, it’s currently unclear whether orlistat was completely to blame for causing liver injury, as some people who experienced this rare side effect were using other medications or had medical conditions that may have contributed to the development of liver injury (11).

Nonetheless, people who are taking medications or have any medical condition, including conditions that impact liver health, should consult their doctor before taking Alli (2).

Even if you’re currently healthy and are not taking any medications, it’s recommended that you consult a registered dietitian or another health professional before taking Alli to ensure it’s appropriate and safe for your specific health needs (2).

Lastly, orlistat should not be taken by those with conditions such as malabsorption, eating disorders like anorexia or bulimia, or cholestasis — a condition that impacts the flow of bile from the liver – and should never be used by people who are pregnant or breastfeeding or by children (2).

Alli diet pills have numerous side effects. They can cause digestive problems and nutrient deficiencies and may interfere with some medications.

Should you try Alli?

Alli diet pills may be effective for promoting small amounts of weight loss when combined with a low calorie, low fat diet and a consistent exercise regimen. However, the effects are not as impressive as most people would like.

At best, you may be able to lose a bit more weight, but only when the medication is combined with a weight loss diet and exercise.

Additionally, the beneficial effects on weight loss need to be weighed against the negative effects of digestive problems and potential nutrient deficiencies.

You’ll also need to eat a calorie-restricted, low fat diet, which may be very pleasing to many people and can lead to nutrient deficiencies if not carefully planned.

Alternatives to Alli

It’s possible to achieve healthy, sustainable weight loss without the use of weight loss supplements like Alli.

If you want to lose weight, consider trying the following:

• Cut back on ultra-processed foods. Cutting back on ultra-processed foods high in refined carbs and added sugars can help promote weight loss. Most of your calorie intake should come from whole, nutrient-dense foods such as vegetables, fruits, nuts, beans, and fish.
• Increase your protein and fiber intake. Protein and fiber are filling and may help you feel more satisfied and less hungry, which may help promote weight loss (12, 13).
• Reduce added sugar intake. Cutting back on added sugar, especially from sugar-sweetened beverages, could help promote weight loss. Plus, cutting out foods and drinks high in added sugars can reduce the risk of heart disease and type 2 diabetes (14, 15).
• Cook more meals at home. Studies show that people who cook more meals at home tend to weigh less and are more likely to have a healthier diet than those who eat more meals out of the home (16).
• Increase activity levels. Increasing energy expenditure by being more active on a daily basis is a healthy way to support weight loss. Try to find an activity you enjoy and stick to it. Walking, swimming, and biking are low impact exercises that are beginner-friendly.
• Work with knowledgeable healthcare professionals. Underlying medical conditions can make weight loss feel impossible. Visit a trusted healthcare professional to rule out potential health conditions that may be impacting your weight.
• Consult a registered dietitian. A registered dietitian is a healthcare professional who specializes in nutrition. A dietitian can help you develop a healthy and sustainable eating plan based on your overall health and specific goals.

In addition to the diet and lifestyle tips listed above, there are other eating plans you can follow that don’t include supplements or medication.

For example, the Mediterranean diet is a non-restrictive, healthy diet that’s been shown to help people lose weight and maintain a healthy body weight over time (17, 18).

According to research findings, Alli may help you lose a bit of weight, but only when combined with a weight-loss-oriented diet and exercise. There are many other ways to promote healthy weight loss that don’t involve diet pills.

Frequently asked questions

How much weight can you lose on Alli?

Research has shown that people taking Alli lost an average of 5.5 pounds (2.5 kg) more over 12 months than people taking placebo treatments.

Keep in mind that this is an average, meaning that some people will lose more weight while taking Alli and others will lose less weight.

Also, most research studies investigating the effects of orlistat have combined orlistat treatment with interventions like low calorie diets or weight loss counseling (5).

This means that taking Alli without making diet or lifestyle changes will likely result in less weight loss.

What foods should you avoid while taking Alli?

Alli is meant to be used alongside a low fat, low calorie diet. This means you should limit your intake of high fat foods and follow a lower calorie diet while taking Alli.

Although it’s necessary to have some fat in your diet when taking Alli, eating high fat foods such as fried foods and ice cream will increase the risk of digestive side effects such as diarrhea.

The Alli website recommends consuming between 12 and 18 grams of fat per meal. To put that into perspective, 1 tablespoon (13.5 grams) of olive oil contains 13.5 grams of fat, and one-quarter of an avocado (76 grams) provides around 8 grams of fat (19, 20).

Can you drink alcohol while taking Alli?

According to the Alli website, it’s safe to drink alcohol when taking Alli.

An older study in 30 people found that taking orlistat with 40 grams of alcohol, which equates to approximately 3 glasses of wine, did not result in adverse side effects or change the way orlistat worked in the body (21).

However, even though a moderate amount of alcohol is safe to consume when taking Alli, it’s important to understand that consuming too much alcohol can negatively impact health in a number of ways and can even make it harder for you to lose weight (22).

The bottom line

Alli is a diet pill that is a low dose version of the prescription-only medication Xenical. Both contain orlistat, which reduces dietary fat absorption in the body.

Research shows that, when combined with a low calorie, low fat diet and exercise, using orlistat could help increase weight loss slightly compared to diet and exercise alone.

However, orlistat products such as Alli and Xenical come with unpleasant and potentially harmful side effects, including fecal incontinence and deficiencies in fat-soluble vitamins.

If you’re interested in trying Alli, be sure to consult a healthcare professional first, because Alli may not be suitable or safe for some people.