Description

Orlistat is a medication used for weight management, specifically for the treatment of obesity. It is available by prescription under the brand name Xenical and over-the-counter as Alli. Orlistat is typically used in conjunction with a reduced-calorie, low-fat diet and a program of regular exercise.

Indications

Orlistat is indicated for:

• Weight loss in overweight or obese adults with a BMI (Body Mass Index) of 30 kg/m² or greater.
• Weight loss in overweight adults with a BMI of 27 kg/m² or greater who also have other risk factors or health conditions, such as high blood pressure, high cholesterol, or diabetes.
• Weight maintenance to help prevent weight regain after initial weight loss.

Mechanism of Action

Orlistat is classified as a lipase inhibitor. Its mechanism of action is localized within the gastrointestinal tract, and it has minimal systemic absorption. Here is how it works:

1. Target Enzymes: Orlistat’s primary targets are gastric and pancreatic lipases, which are enzymes in the stomach and small intestine responsible for breaking down dietary fats (triglycerides).
2. Inhibition: Orlistat works by forming a covalent bond with the active serine residue on these lipases. This binding inactivates the enzymes, preventing them from functioning.
3. Preventing Fat Digestion and Absorption: With the lipases inhibited, dietary triglycerides are not hydrolyzed into smaller, absorbable free fatty acids and monoglycerides.
4. Caloric Deficit: As a result, approximately 30% of the fat consumed in a meal remains undigested and is not absorbed by the body. This unabsorbed fat is then excreted in the feces, leading to a caloric deficit that promotes weight loss.

Because of this mechanism, the most common side effects of orlistat are gastrointestinal in nature, such as oily spotting, gas with discharge, and loose stools.