Supplement: Alli Diet Pills

supplement capsules

Will Alli help with weight loss?

Orlistat is a pharmaceutical drug, sold over-the-counter under the name Alli, and under prescription as Xenical.  It has been on the market since 1999.  In 2007, it was released for over-the-counter sales under the name Alli.  The difference between the two pills, Alli and Xenical, is dosage.  Alli is 60 mg per pill and Xenical is 120 mg per pill.  


How does it work?  Orlistat was developed to treat obesity, but it was not meant to treat obesity without accompanying exercise and diet changes.   Orlistat is meant to be taken with a low-fat, lower-calorie diet.  The drug is a lipase inhibitor.  Lipase is the enzyme released by the pancreas into the small intestine to digest fats and allow you to absorb them for energy.  Simply put, the pill works by reducing the breakdown of fat in the gut and thus allowing fewer calories from fat to be absorbed. By preventing the action of lipase, the medication allows fats to just pass out of the colon undigested.  Orlistat taken with each meal prevents the absorption of all the fat from the food into the body.  

Orlistat Mechanism
Orlistat Mechanism

Side effects:  I am sure you know the most common side effect, or at least you can figure it out.  The most common side effects of Orlistat come from the increased fat in the colonic excretions.  The increase in bowel fats causes gas (aka flatulence), oily bowel movements, and other bowel-related changes. The worst of the symptoms is stool leakage.  Imagine a pair of white pants in church, and you thought it was just gas.  

Alli Diet Pills
Alli Diet Pills
WARNING!!! Black Box Warning!
There is a black box warning for Orlistat from 2010 because it can cause severe liver damage. You must be on the lookout for jaundice (yellow coloring of skin and eyes), itching, loss of appetite, and brown urine or yellow stools. Reports of severe liver damage in about a dozen people who used orlistat prompted a new warning label in 2010, though the FDA could not confirm that the drug caused the damage. People who take the drug should watch for signs of liver malfunction such as yellow skin or eyes, itching, loss of appetite, brown urine, or yellowish stool.


  1. A 2005 study was performed on obese adolescents and found that 25% of the test group experienced a 5% decrease in BMI.  That is compared to 15% of the placebo group​[1]​.  This shows that it is effective at assisting with weight loss, but up to 50% of the subjects experienced gas and/or diarrhea.  
  2. According to the Mayo Clinic, a 2014 review found that people who dieted, exercised, and took Alli for at least a year lost about 5.5 pounds (2.5 kilograms) more on average than those who dieted and exercised alone​[1]​.  
  3. One last review from 2014 showed that Orlistat was effective in both the 120 mg and 60 mg dosage​[2]​.  It showed three basic findings:
    • The benefits of weight loss are dose-dependent, meaning that 120mg worked better than 60 mg.
    • The GI symptoms were worse with the higher dose but were present for both.
    • Behavior changes such as diet and exercise increased weight loss.  
  4. Another study by Woo looked at Orlistat with and without post-treatment nutrition-led interventions and education.  They found that without post-treatment nutritional intervention and behavior changes, the subjects gained the weight back​[1]​.
  5. One last study shows that the low carbohydrate was as effective as Orlistat and a low-fat diet.  The other interesting finding from his study was that the low carbohydrate diet was slightly more effective at lowering blood pressure​[2]​.  
Fat Pants
Fat Pants

Does it work?  Yes.  There are plenty of studies that show it works.  A review by Drew showed that Orlistat increased weight loss by about 3% compared to without it​[3]​.  If a 5% weight loss is required to impact health, then 3% is a clinically significant addition to normal diet and exercise for those that are obese.  A reduction of 5-10 pounds has been shown to reduce your risk of high blood pressure, diabetes type 2, and heart disease.  There are plenty of studies that show Orlistat helps lower these risks.  One study showed that 1 Kg of body weight loss reduced a patient’s diabetes type 2 risk by 16%​[4]​.  The same study showed a reduction in all-cause mortality with intentional weight loss.  

Side effects: This is a big reason to avoid this medication.  This drug has gastrointestinal side effects, including but not limited to loose, oily stools, flatulence, and frequent, foul-smelling bowel movements that you may be unable to control. This is all caused by the increased fat composition of the stools.  This reduction in fat absorption may also cause a reduction in the absorption of fat-soluble vitamins, such as vitamins A, D, E, and K, and thus a deficiency in them.  

The bottom line:  I would not recommend this treatment. It is an older drug, so you might wonder if it is still for sale, but I have confirmed it is still on the shelves at Target. Discuss this with a provider before you try this OTC or prescription medication.  This is not a medication for quick weight loss for a prom, company function, or social event.  I usually insist that patients see a trainer and dietician.  You must be on a low-fat diet while taking Orlistat to minimize the abdominal side effects.  I would carefully consider the alternative.  The side effects are embarrassing enough to force you to become a hermit in the woods, so I would not take this unless it is your last option.


  1. [1]
    J. Woo et al., “Effectiveness of a lifestyle modification programme in weight maintenance in obese subjects after cessation of treatment with Orlistat,” J Eval Clin Pract, pp. 070728052316007-???, Jul. 2007, doi: 10.1111/j.1365-2753.2006.00758.x. [Online]. Available:
  2. [2]
    W. S. Yancy Jr et al., “A Randomized Trial of a Low-Carbohydrate Diet vs Orlistat Plus a Low-Fat Diet for Weight Loss,” Arch Intern Med, p. 136, Jan. 2010, doi: 10.1001/archinternmed.2009.492. [Online]. Available:
  3. [3]
    B. Drew, A. Dixon, and J. Dixon, “Obesity management: update on orlistat.,” Vasc Health Risk Manag, vol. 3, no. 6, pp. 817–21, Jan. 2007 [Online]. Available:
  4. [4]
    D. Lau and H. Teoh, “Current and Emerging Pharmacotherapies for Weight Management in Prediabetes and Diabetes.,” Can J Diabetes, vol. 39 Suppl 5, pp. S134-41, Dec. 2015, doi: 10.1016/j.jcjd.2015.10.001. [Online]. Available:
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About the Author

I am a family physician who has served in the US Army. In 2016, I found myself overweight, out of shape, and unhealthy, so I made a change to improve my health. This blog is the chronology of my path to better health and what I have learned along the way.

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