Diet Pills: What You Need to Know

Diet pills are a tempting quick fix for an increasingly overweight American populace. See more drug pictures.
Photo courtesy Amazon.com

Their ads claim they can help you "feel more fit," "boost your energy" and "melt away the pounds." Who needs diet and exercise when a little pill can erase the weight quickly and easily? With more than 60 percent of Americans now considered overweight or obese, diet drugs have turned into a multibillion dollar industry in the United States.

But although diet pills promise a quick fix, can they deliver? Can they help you lose weight? And if so, can they help you keep it off? Weight-loss questions aside, several diet drugs over the last decade have been associated with serious heart problems and other health-related issues, and diet pills have even been linked to a number of deaths.

Diet drugs are available in several different forms, including prescription drugs, over-the-counter drugs and herbal supplements.

­

­Prescription drugs such as Meridia and Xenical are only available with a doctor's prescription. They are carefully regulated by the Food and Drug Administration (FDA) Center for Drug Evaluation and Research, and their use is closely monitored by the prescribing doctor.

Over-the-counter drugs are available without a doctor's prescription, right in your local drugstore or supermarket, and are also regulated by the FDA. According to AnneCollins.com, "Products considered by FDA to be over-the-counter weight control drugs [as opposed to dietary supplements] are primarily those containing the active ingredient phenylpropanolamine (PPA)." In 2000, the FDA requested that drug manufacturers voluntary reformulate PPA-containing products in the wake of evidence that phenylpropanolamine can increase the risk of stroke, so there are few diet drugs on the market that still contain this ingredient. OTC drugs also fall under the jurisdiction of the FDA's Center for Drug Evaluation and Research.

Herbal diet supplements are also available without a prescription. You'll typically find a huge variety of these in health food and nutrition stores as well as in regular supermarkets. Herbal supplements are often labeled "all natural" and are considered by the FDA to be food products as opposed to drugs. As such, they fall under the jurisdiction of the FDA's Center for Food Safety and Applied Nutrition and are regulated differently from OTC drugs.

­ There is also a selection of diet aids that are administered by patch, as a powder or in liquid form. These types of drugs may fall into any of the above categories -- it is only the delivery method that is unique.

In this article, we will look at the wide variety of diet pills available, find out how they work and what their side effects are and see if they live up to their promises.

Prescription Diet Pills

Different diet pills work in different ways depending on which ingredients they contain.

Appetite suppressants such as sibutramine (Meridia), diethylpropion (Tenuate) and phentermine (Adipex-P, Fastin, Anoxine-AM, etc.) affect the appetite-regulating region of the brain called the hypothalamus. They work by blocking the re-uptake of the chemicals serotonin and norepinephrine, which create that feeling of satiety you get after eating a big meal. With more of these chemicals circulating in your brain, you feel full, so you eat less.

Prescription fat blockers, such as orlistat (Xenical), inhibit the action of an enzyme called lipase. When we eat foods with fat in them, lipase normally breaks down the fat when it gets to the intestinal tract. With a lipase inhibitor in effect, a percentage of the fat ingested is removed from the body through bowel movements instead of being broken down and absorbed.

Many prescription drugs are used as diet aids even though that was not their intended purpose. Some antidepressants are used "off-label" as diet aids because they have been shown in studies to help patients lose weight and keep it off for several months. Researchers are also studying certain drugs normally used to treat epilepsy (topiramate and zonisamide) and diabetes (metformin) for their weight-loss potential.

Because diet pills are such a lucrative business, pharmaceutical companies are pushing to introduce more products to the market. More than 100 new weight-loss medications are either in development or in clinical trials as of January 2005. One of the most promising is rimonabant (Acomplia), which acts on a protein in the brain called the endocannabinoids. Endocannabinoids are similar in structure to the active ingredient in cannabis (marijuana) and may be responsible for appetite control. Rimonabant blocks the endocannabinoids from reaching their receptors in the brain. (See Study: Marijuana-like substances control appetite to learn more.) By blocking this protein, the drug reduces food cravings. In clinical trials, one-third of obese people who were given Acomplia lost more than 10 percent of their body weight and were able to keep it off for up to two years. The drug also has a few welcome side effects: It increases HDLs ("good cholesterol") while lowering triglycerides (a form of fat that is carried in the bloodstream). Acomplia may even help smokers kick the habit.

Other promising drugs affect appetite-related hormones. One blocks ghrelin, which the stomach sends to the brain to increase appetite. Another mimics a hormone called PYY, which tells the body it's full.

Who Should Use Prescription Diet Pills?

Prescription diet pills aren't for the person who wants to shed a few pounds to fit into a holiday party dress or tuxedo. Only people who are "obese" (those who are 30 percent over their ideal weight, or have a Body Mass Index (BMI) of 30 or more -- see National Heart, Lung and Blood Institute: Healthy Weight to calculate your BMI) or who have a history of high blood pressure or diabetes are good candidates for prescription diet medications, according to the National Institutes of Health (NIH).

Even though approximately 16 percent of American children are overweight, most diet pills are not recommended for use by children under the age of 16. The exception is orlistat, which can safely be used by teens 12 and older.

If you watch late-night TV, you know that it seems like every other ad is touting the miraculous claims of the latest over-the-counter diet pill. Read on to find out about OTC diet pills.

OTC Diet Pills

OTC Dexatrim
OTC Dexatrim
Photo courtesy Amazon.com

Some over-the-counter pills (such as Xenedrine, Dexatrim and Zantrex-3) once used a powerful combination of the stimulant ephedra and caffeine to help users shed pounds. They reportedly worked in combination by increasing energy expenditure -- or thermogenesis (it is thought that caffeine increases metabolism by increasing the breakdown of fatty acids) -- and reducing appetite (ephedrine acts on the satiety center in the hypothalamus). But since late 2003, when the FDA banned the sale of ephedra-containing drugs due to evidence of increased risk of heart attack, these formulations have replaced ephedra with a mixture of vitamins (such as thiamin, riboflavin, vitamin B-6, folic acid), an ephedra-like substance called synephrine that is found in certain citrus fruits, and caffeine. The combination reportedly increases energy while boosting metabolism.

There are many herbal weight-loss supplements on the market today, and they utilize different mechanisms to reportedly aid in dieting. Here are some of the more common ingredients and their reported weight-loss mechanisms:

  • Herbal ephedra, caffeine, guarana and country mallow - Increase metabolism
  • Guar gum, glucomannan and psyllium - Cause a "full" feeling
  • Hydrocitric acid, green tea, conjugated linoleic acid and pyruvate - Slow fat production
  • Chitosan (or chitin - substance found in the exoskeleton of shrimp and other shellfish) - Block fat from being absorbed

So as you can see, there are a lot of diet pills out there, all claiming to help you lose weight in one way or another. But do they really work? And what kinds of side effects can you expect?

­

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.
Photo courtesy Amazon.com

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 on the next page.

Related HowStuffWorks Articles

More Great Links

Sources

  • Connolly, Heidi M., Ph.D., et al. Valvular Heart Disease Associated with Fenfluramine-Phentermine, July 8, 1997.http://www.cnn.com/HEALTH/9707/08/fenphen.report/
  • Crabtree, Penni. "Ephedra Found to Change Heart Rhythm." The San Diego Union-Tribune, January 14, 2004.
  • Diet Pills and Weight Loss.http://www.annecollins.com/diet-pills.htm
  • Ephedra, MayoClinic.com http://www.mayoclinic.com/invoke.cfm?objectid=17D4A42C-508B-D3DD-172C3E9C89950B3A
  • FDA Announces Withdrawal of Fenfluramine and Dexfenfluramine, Press Release, September 15, 1997. http://www.fda.gov/cder/news/phen/fenphenpr81597.htm
  • Kolata, Gina. Obesity Drug Stirs Hope, Hype. The Barre Montpelier Times Argus, December 5, 2004. http://www.timesargus.com/apps/pbcs.dll/article?AID=/20041205/NEWS/412050361/0/FRONTPAGE
  • National Center for Health Statistics, Overweight Prevalence 1999-2002. http://www.cdc.gov/nchs/fastats/overwt.htm
  • National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), Prescription Medications for the Treatment of Obesity. NIH Publication No. 04-4191. November 2004. http://win.niddk.nih.gov/publications/prescription.htm
  • Peck, Peggy. "Experimental Diet Drug has Staying Power." WebMD Medical News, November 9, 2004.
  • Prescription Diet & Weight Loss Pillshttp://www.diet-i.com/diet_pills/prescription-diet-pills.htm
  • Raloff, Janet. Diet Pills: It's Still Buyer Beware, Science News Online, August 10, 2002. http://www.sciencenews.org/articles/20020810/food.asp
  • 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, ConsumerReports.org, December 2003. http://www.consumerreports.org/main/detailv4.jsp?CONTENT%3C%3Ecnt_id=359183&FOLDER%3C%3Efolder_id=162687&bmUID=1104253159138