Weight Loss Pills That Block Calories

Very few weight-loss pills have been proved safe and approved by the Food and Drug Administration. The Mayo Clinic notes that only three weight loss drugs are currently FDA-approved, and only one -- orlistat -- is approved for long-term use. Sold over-the-counter under the brand name Alli, the pill blocks the absorption of about 25 percent of the calories you consume from dietary fat. Dietary and herbal supplements do not undergo the same rigorous testing and clinical trials as prescription medications and may not be safe for everyone. Always talk to your doctor before taking any type of weight loss drug.

Orlistat

Sold by prescription as Xenical and in a smaller dose over the counter as Alli, orlistat works by disabling the enzyme lipase. Lipase is used to break down dietary fat in your intestine. Orlistat stops this digestion and allows fat to pass through your body without it -- or its calories -- being absorbed. About 25 percent of the fat you eat won't be digested. You must follow a strict low-fat diet when using orlistat; eating more than 15 g of fat at any meal can result in some of orlistat's less pleasant side-effects -- gas with an oily discharge and uncontrollable diarrhea -- both excellent motivators to stick to your diet.

Phentermine

One half of the dangerous diet pill sensation "fen-phen," that was removed from the market in the 1990s; phentermine by itself is approved for use as a short-term weight loss aid. Phentermine can be habit-forming and it isn't recommended to use it longer than six weeks. Technically, phentermine does not block any of the calories you consume -- it simply helps you consume fewer calories by acting as an appetite suppressant. It's recommended to follow a reduced calorie diet and exercise regularly while using phentermine. Side-effects include rapid heartbeat, elevated blood pressure and insomnia.

Diethylpropion

Durad, Tenuate and Tepanil are brand names for diethylpropion, another appetite-suppressing drug approved by the FDA for short-term weight-loss. The drug affects the appetite center in your brain to reduce food cravings and causes a reduction in hunger. Eating less food should result in weight loss. Diethylpropion can be habit-forming and is not suitable for people who are allergic to amphetamines. Alcohol and sedatives can not be used while taking Tenuate and you may experince symptoms of withdrawal if you stop taking diethylpropion suddenly.