Should you take “Alli” for your weight loss program?

Orlistat (marketed as a prescription under the trade name Xenical by Roche or over-the-counter as Alli by GlaxoSmithKline), also known as tetrahydrolipstatin, is a drug designed to treat obesity.

Its primary function is preventing the absorption of fats from the human diet, thereby reducing caloric intake.

It is intended for use in conjunction with a physician-supervised reduced-calorie diet.

The effectiveness of orlistat in promoting weight loss is definite, though modest.

Pooled data from clinical trials suggests that people given orlistat in addition to lifestyle modifications, such as diet and exercise, lose about 2–3 kilograms (4.4–6.6 lb) more than those not taking the drug.

Orlistat also modestly reduces blood pressure, and appears to prevent the onset of type 2 diabetes, whether due to weight loss itself or to other effects; in a large randomized controlled trial, orlistat was found to reduce the incidence of diabetes by nearly 40% in obese people.

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Side Effects

Orlistat is notorious for its gastrointestinal side effects (sometimes referred to as treatment effects), which can include steatorrhea (oily, loose stools) and fecal incontinence.

These decrease with time, however, and are the only significant adverse effects of the drug, which appears to be safe for long-term use.

In the United States, the European Union, and Australia, orlistat is available for sale without a prescription. Over-the-counter approval was controversial in the United States, with consumer advocacy group Public Citizen repeatedly opposing it on safety and efficacy grounds.

As of October 2009, no generic formulations of orlistat are available.