Weight Loss Using Xenical or Alli: A Review of Orlistat

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Many weight loss drugs compete for the lucrative market of obesity. Amongst those, Xenical and Alli have become in recent years some of the most popular brands in that particular market. But how should they be used and how do they work?

alli (orlistat)

How Does Orlistat Work?

Xenical and Alli both contain the same molecule called orlistat and are manufactured by the same company, Roche Pharmaceuticals. Xenical contains twice the dosage of orlistat found in Alli pills, which is why only Alli is available over-the-counter while Xenical needs to be prescribed.

Orlistat works by preventing the intestines from absorbing part of the fat contained in food. About one-third of eaten fat therefore goes through the intestines and is evacuated in the bowel movements. Xenical or Alli do not have any impact on appetite. In other words, it does not decrease the feeling of hunger throughout the day, unlike most other FDA-approved weight loss drugs.

Alli or Xenical should therefore be taken only as a diet supplement. Taking orlistat without any significant dietary change will not bring any weight loss. Instead, it will cause diarrhea, which is one of the most common side effects of orlistat.

Common Side Effects of Xenical and Alli

Because of the way orlistat works, all undigested fat ends up in the stools. Therefore, eating an excessive amount of fatty food causes the evacuation of a large amount of fat. This can cause severe and urgent diarrhea, fatty stools or even fecal incontinence. While taking Xenical or Alli, it is therefore extremely important to stick to a low-fat diet for the duration of the treatment.

Other minor side effects reported for orlistat include fever, sore throat, runny nose, excessive sweating and fatigue. If those symptoms persist, it is advisable to consult a doctor.

Is Weight Loss Achievable With Xenical and Alli?

Yes, it is, but only if orlistat is taken in conjunction with a sensible low-fat diet. Studies have shown that orlistat does indeed have a positive impact on weight loss. However, after discontinuing treatment, a significant proportion of patients have regained some or all of their original weight. Sticking to a sensible diet is therefore extremely important, even after the end of the treatment.


The information contained in this article is for educational purposes only and should not be used for diagnosis or to guide treatment without the opinion of a health professional. Any reader who is concerned about his or her health should contact a doctor for advice.