Unlike over-the-counter diet pills, prescription weight-loss medications are regulated by the FDA and have been tested in clinical trials for safety and efficacy. That said, most health experts agree that these diet pills won't lead to dramatic weight loss, and they may have unpleasant side effects. The two most popular prescription diet pills are orlistat (Xenical) and sibutramine (Meridia). They are approved for obese patients with a BMI over 30. The problem with both of these diet pills is that they don't lead to significant weight loss. A meta-analysis conducted by The Obesity Society showed that patients on orlistat for one year lost an average of 6 pounds more than those who took a placebo. Six pounds over the course of a year is certainly not a lot, especially when you have to deal with gastrointestinal side effects like sudden diarrhea and oily spotting. The Obesity Society had much the same result when it studied sibutramine trials -- participants lost an average of 12 pounds more over the course of a year than the placebo group.
In addition, The Mayo Clinic advises that most patients taking prescription weight-loss medications regain the weight they've lost once they stop treatment. Public Citizen lists both Xenical and Meridia on its "do not use" list.
The best information on prescription diet pills comes from The Obesity Society, publishers of the journal Obesity. The Obesity Society performs a meta-analysis on both Xenical and Meridia to determine if these medications lead to significant weight loss. An article published in the British Medical Journal also conducts similar research on prescription diet pills. In addition to these sources, organizations like Public Citizen, the Mayo Clinic and Consumer Reports publish solid summaries of the latest research.
1. The Obesity Society
This meta-analysis conducted by The Obesity Society shows that prescription diet pills, like orlistat (Xenical) and sibutramine (Meridia), lead to only very moderate weight loss.
Review: Principles of Pharmacotherapy in the Management of Obesity, Editors of The Obesity Society
2. British Medical Journal
This article in the British Medical Journal examines 30 double-blind placebo controlled studies lasting between one and four years to compare the effectiveness and adverse effects of prescription diet drugs. All three are found to produce modest weight loss, but with side effects.
Review: Long Term Pharmacotherapy for Obesity and Overweight: Updated Meta-analysis, D. Rucker, et al, Nov. 15, 2007
3. Public Citizen
Public Citizen includes both Xenical and Meridia on its "do not use" list due to the risk of potentially dangerous side effects. Public Citizen has also petitioned the FDA to remove Xenical from the market.
Review: Worst Pills, Best Pills, Editors of Public Citizen
4. National Public Radio
The National Institutes of Health warns that prescription diet drugs "should be used only by patients who are at increased medical risk because of their weight."
Review: Prescription Medications for the Treatment of Obesity, Editors of the National Institutes of Health
5. Mayo Clinic
The Mayo Clinic notes that prescription diet pills can help some patients, but they caution that most regain the weight they've lost after they stop treatment.
Review: Weight-loss Drugs: Can a Prescription Help You Lose Weight?, Editors of the Mayo Clinic, Feb. 15, 2008
Consumer Reports interviews a health expert who reports that compliance with Xenical is very poor due to its side effects and negligible benefit. Public Citizen Director Dr. Sidney Wolfe also explains his organization's opposition to Xenical.
Review: Fat-blocking Drug: Should You Use It?, Editors of ConsumerReports.org, June 2006