Prescription Diet Pills

Doctor-prescribed weight-loss medications

Research about prescription weight-loss drugs is much more prevalent and credible due to the far stricter controls imposed on these drugs. At least there are long-term medical studies and FDA jurisdiction. However, just because these products have FDA approval doesn't actually mean they work -- or work without unpleasant side effects. Furthermore, the FDA's approval of orlistat (Xenical) for over-the-counter use has many watchdog organizations concerned.

The medications that are currently available for prescription weight loss are phentermine (under several trade names including Adipex-p, Obenix and Oby-Trim), sibutramine (Meridia in the U.S. and Reductil in Europe) and orlistat (Xenical). These medications are approved for people who are obese -- defined as having a body mass index (BMI) of 30 or more. Only orlistat and sibutramine are approved for long-term use. The FDA originally approved phentermine in 1973. According to The Obesity Society, "phentermine was approved ...; when the criteria needed for approval were less rigorous than they are today. Therefore, fewer studies have evaluated the efficacy and safety of phentermine therapy than have evaluated sibutramine and orlistat."

Do prescription diet drugs work? Here again, the answer isn't simple. Most studies show that users do lose a few more pounds with prescription weight-loss medications than those who don't take the pills. The Obesity Society, which publishes the influential journal Obesity, performed a meta-analysis of 11 studies that tested orlistat for at least one year. According to the society, "all trials found a statistically significant beneficial weight loss of orlistat therapy." On average, participants in these studies lost about 6 pounds more than those who received a placebo. In a meta-analysis of sibutramine (Meridia) trials, participants lost about 9.5 pounds more than the placebo group.

In a WebMD.com study, obese people who modified their eating and exercise habits and took Meridia actually lost more weight than those who took the drug alone or those who only modified their eating and exercise habits.

While most studies show some weight loss with these prescription medications, they also show that most people regain most (if not all) of the weight when they stop taking the pills. According to the Mayo Clinic, phentermine is no longer prescribed as often as orlistat or sibutramine, mainly because phentermine is only approved for short-term use. The Mayo Clinic finds that most prescription diet pills need to be taken "indefinitely," since the weight usually returns when patients stop taking medication. As a result, the drugs approved for long-term use -- Xenical (orlistat) and Meridia (sibutramine) -- are more popular. However, the National Institutes of Health cautions that neither of these drugs has been proven safe or effective beyond the two-year mark.

Phentermine

Phentermine diet pills are appetite suppressants that have been around for years. They are chemically similar to amphetamines, or stimulants, that suppress the appetite and cause you to eat less. Back in the 1990s, the combination Fen-Phen (phentermine plus fenfluramine) was thought to be a highly effective diet drug for a couple of years until studies linked fenfluramine to heart valve disease. As a result, the FDA asked that it be pulled from the market. On its own, phentermine can work to suppress the appetite and provide short-term weight loss. Phentermine is designed to be used in conjunction with a calorie-restricted diet and exercise regimen, and it's indicated for usage of less than 12 weeks. When taken for longer than 12 weeks, studies show that phentermine can raise blood pressure and become addictive.

Surprisingly, there are not that many clinical studies of phentermine by itself, despite its having been around since the 1950s. Plenty of studies were done of the drug in combination with fenfluramine, but it was rarely studied on its own. According to the Obesity Society, the only long-term study of phentermine was conducted in 1968. The study, which was published in the British Medical Journal, tracked 108 women who received phentermine or a placebo. After 36 weeks, the women taking a daily dose of phentermine lost 13 percent of their body weight, compared to 5 percent for the placebo group.

Sibutramine (Meridia)

Sibutramine (Meridia) is also an appetite suppressant, affecting a person's feeling of fullness so they feel satisfied eating less food. Studies say the positive effects of Meridia tend to max out at six months and it can raise your heart rate and blood pressure, which must be carefully monitored. The Obesity Society finds that a daily dose of sibutramine (10 to 15 mg) increases blood pressure a few points and raises heart rate by four to six beats per minute. In outlining the pros and cons of Meridia in 2004, HealthFacts points to 11 clinical trials ranging from 12 to 52 weeks in which persons taking Meridia at varying doses lost an average of 10 to 14 pounds over a year. Any weight loss is positive, of course, but that's roughly one pound per month.
HealthFacts also points out that weight lost was regained when patients stopped taking the medication.

Orlistat (Xenical)

Orlistat (Xenical) works by blocking fat absorption so that it moves through the intestine undigested. The idea of a fat blocker sounds good in theory until you consider the not-so-pleasant side effects, which include sudden diarrhea and "leakage." Those side effects go down as your fat intake does. Several articles we read suggest ironically that Xenical may work best as a deterrent, whereby eating less fat you reduce your chances of nasty side effects. While gastrointestinal side effects are the most common, Xenical can also reduce the absorption of fat-soluble vitamins. Experts recommend taking a regular multivitamin while using Xenical. As mentioned above, The Obesity Society's meta-analysis of 11 Xenical trials showed that users lost an average of about 6 pounds more than those who took a placebo.

In 2006, the consumer advocacy group Public Citizen called for the FDA to pull both Meridia and Xenical from the shelves. In the case of Meridia, Public Citizen cites 49 deaths from cardiac arrest linked to the drug and 124 reports of cardiac problems developed by those taking the drug. With Xenical it is the threat of colon cancer that is cause for concern, as Xenical has been shown to increase aberrant crypt foci (ACF) cells in the colon in rats. ACF cells are widely thought to be a precursor to colon cancer. Xenical also has those aforementioned side effects that make the drug difficult for many people to tolerate. ConsumerReports.org has written articles about both medications and says you'd do better to stick with old-fashioned diet and exercise.

Public Citizen lists all of these prescription diet drugs on their "do not use" list, saying that the small weight loss achieved is not worth the side effects and potential health risks.