Losing weight can be very difficult.

Some studies show that 85% of people fail using conventional weight loss methods (1).

This causes many people to seek alternative methods, such as diet pills, for help.

Alli is one such diet pill, but is a pharmaceutical drug rather than a plant-based supplement.

This drug limits the amount of dietary fat our bodies absorb, which reduces calorie intake and leads 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 over-the-counter version of a pharmaceutical weight loss drug called orlistat.

The prescription-only version is called Xenical, which contains a higher dosage. Alli diet pills contain 60 mg of orlistat, while Xenical pills contain 120 mg.

This drug was first approved by the FDA in 1999. It is usually prescribed for long-term obesity management, alongside a low-fat, calorie-restricted diet.

Bottom Line:

Alli is the over-the-counter version of orlistat, a pharmaceutical drug used to manage obesity. It is also available by prescription as Xenical.

How Does Alli Work?

Alli works by preventing the body from absorbing dietary fat.

Specifically, it blocks an enzyme in the gut called lipase.

Lipase is essential to the digestion of the fats we eat. It helps break down fats into free fatty acids that can be picked up by the body.

Without this enzyme, dietary fat bypasses digestion and is then expelled from the 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 the body, which can lead to weight loss.

Bottom Line:

Alli interrupts the digestion of dietary fats and blocks about 30% of fat from being absorbed. This leads to an overall reduction in calorie intake.

Alli Can Help You Lose Small Amounts of Weight

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

The most well-known is the Swedish XENDOS study, which included 3,305 overweight individuals and lasted for 4 years (3).

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, and limit dietary fat to 30% of calories. They were also encouraged to go for walks every day.

This graph shows the weight changes in the two groups over 4 years (3):

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).

As shown on the graph, 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 placebo.

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

More Studies

According to a review study, the average 12-month weight loss for adults taking orlistat is about 7.5 lbs (3.4 kg) greater than placebo (4).

This amounts to 3.1% of initial weight, which is not particularly impressive. It also appears that weight is slowly regained after the initial year of treatment.

Interestingly, one study showed that a drug-free low-carb diet was just as effective as both orlistat and a low-fat diet combined (5).

Bottom Line:

Alli/orlistat is a mildly effective anti-obesity drug, with the average weight loss at 12 months being 3.4 kg (7.5 lbs) greater than placebo.

Do Alli Diet Pills Have Any Other Health Benefits?

Alli has also been linked to several other health benefits, possibly due to the weight loss effects.

  • Reduced type 2 diabetes risk: In the XENDOS study, 4-year use of orlistat reduced the risk of developing type 2 diabetes by 37% (3).
  • Reduced blood pressure: Studies show that Alli may lead to mild reductions in blood pressure (6, 7).
  • Reduced total- and LDL-cholesterol: Studies show that Alli can positively influence cholesterol levels (6, 8).
Bottom Line:

Prolonged use of Alli may reduce the risk of type 2 diabetes and help protect against heart disease.

Side Effects, Dosage and How To Use

Alli diet pills do have some well-documented side effects that are worth noting (9).

As they 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.

Continued use of Alli can also impair the absorption of fat-soluble nutrients like vitamins A, D, E and K.

For this reason, taking a multivitamin along with treatment is recommended.

Alli may also interfere with the absorption of some medications, and a few cases of liver failure and kidney toxicity have been reported.

People who are taking medications or have any sort of medical condition should consult with their doctor before taking Alli diet pills.

Based on the limited long-term data available, most clinical guidelines recommend that Alli is not used continuously for more than 24 months.

The optimal dosage used in the studies is 120 mg, three times per day.

Bottom Line:

Alli diet pills have numerous side effects. They can cause digestive problems and nutrient deficiencies, and may also interfere with some medications. The best studied dosage is 120 mg, three times per day.

Should You Try Alli?

Alli diet pills are among the very few weight loss aids that actually work to some extent. 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 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.

Not to mention, you also need to eat a calorie-restricted, low-fat diet, which is not very pleasing to many people.

If you really want to lose weight and keep it off, then eating more protein and fewer carbs is a much more effective and sustainable approach.