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Diet Pills: What You Need to Know

Do Diet Pills Really Work?

"All natural" dietary supplements often contain synephrine, an ephedra-like compound derived from certain citrus fruits.
"All natural" dietary supplements often contain synephrine, an ephedra-like compound derived from certain citrus fruits.
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Many over-the-counter diet pill manufacturers say their product will help you see miraculous weight loss -- like losing up to 30 pounds in 30 days -- without diet or exercise. Their claims sound too good to be true, and most of them are.

A few pills, especially the newer prescription varieties (such as Meridia and Xenical), have been shown in clinical studies to help dieters shed a few pounds. But the majority of the ads you see on the Internet and TV are for products that are unregulated, untested and unproven.


Even the most effective diet pills are only meant to be taken for a short period of time -- usually six months or less. During that time, doctor-prescribed weight-loss drugs can trim anywhere from 5 to 22 pounds, or up to 10 percent of your body weight. But after six months, your body develops a tolerance to these drugs' effects, and weight loss plateaus. After that, if you don't also follow a healthy eating and exercise plan, the weight will come right back.

Side Effects of Diet-pill Use

Different diet pills contain different ingredients, so their side effects vary:

As fat blockers like orlistat (Xenical) remove excess fats via the intestines, they may cause uncomfortable cramping, gas and diarrhea. Because these drugs also reduce the body's absorption of essential vitamins and nutrients, people who take Xenical are advised to take a daily multivitamin supplement.

Sibutramine (Meridia) and other similar appetite suppressants stimulate the sympathetic nervous system, which can raise blood pressure and heart rate. This increases the risk of heart attack and cardiac arrest, especially among people who already suffer from high blood pressure, irregular heartbeat or heart disease. In fact, between February 1998 and March 2003, the FDA received reports of 49 deaths related to sibutramine. Other, more minor side effects include constipation, headache, dry mouth and insomnia (because the chemicals in these drugs also influence sleep patterns).

Herbal diet pills, even though they're "all natural," can have potentially dangerous side effects depending upon their ingredients. "Herbal" doesn't necessarily mean "safe." Also, because they are considered part of the food industry and are therefore regulated differently by the FDA, there is no guarantee that they can live up to their manufacturers' claims.

To find out more about diet pills and related topics, check out the links below.

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More Great Links


  • Connolly, Heidi M., Ph.D., et al. Valvular Heart Disease Associated with Fenfluramine-Phentermine, July 8, 1997.
  • Crabtree, Penni. "Ephedra Found to Change Heart Rhythm." The San Diego Union-Tribune, January 14, 2004.
  • Diet Pills and Weight Loss.
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  • FDA Announces Withdrawal of Fenfluramine and Dexfenfluramine, Press Release, September 15, 1997.
  • Kolata, Gina. Obesity Drug Stirs Hope, Hype. The Barre Montpelier Times Argus, December 5, 2004.
  • National Center for Health Statistics, Overweight Prevalence 1999-2002.
  • National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), Prescription Medications for the Treatment of Obesity. NIH Publication No. 04-4191. November 2004.
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  • Prescription Diet & Weight Loss Pills
  • Raloff, Janet. Diet Pills: It's Still Buyer Beware, Science News Online, August 10, 2002.
  • Stein, Rob. "Seeking a Slim Victory, Drugmakers Press FDA: Pipeline is Bulging with Diet Pills." The Washington Post, September 17, 2004.
  • Weight-loss Drug Fattens Heart Risks,, December 2003.