Prescription weight-loss drugs do not guarantee success, but physicians are prescribing them under certain circumstances.
Physicians are encouraged to follow professional guidelines when prescribing weight-loss medications. The current guidelines stress that a lifestyle weight-loss program should always be the primary treatment for obesity. Medications, if used, should be a secondary treatment and their use limited to obese individuals (or individuals who are overweight and have weight-related health complications).1
How Weight-Loss Drugs Work
The prescription weight-loss drugs on the market today work in one of two ways. One group works on brain neurotransmitters (chemicals that communicate between nerve cells) to reduce appetite. Examples of these drugs include diethylpropion (brand name Tenuate), phendimetrazine (many brand names including Bontril, Adipost, Anorex-SR, Appecon ) and phentermine (many brand names including Adipex-P, Ionomin, Obenix, Oby-Trim).
The second type of weight-loss medication works in the intestines to prevent fat calories from entering the body. Orlistat (brand name Xenical) is the only drug currently available by prescription that works in this way.
The short-term side effects of certain drugs to treat depression, seizures, or diabetes include weight loss. These drugs have not been approved by the FDA for use as weight-loss drugs. 2
Calories Still Count
Taking a prescription weight-loss medication does not guarantee weight loss. Calories still count and drugs should be combined with efforts to change diet and physical activity. The drugs support this effort by helping the person taking them reduce caloric intake (by suppressing appetite or preventing fat absorption). Average weight loss is 5-10% of initial body weight. 3 And, as is common with many drugs, some people simply don't respond at all.
Risk of Side Effects
As with all medication, weight-loss drugs have potential side effects. Appetite suppressants can cause nervousness and sleeplessness. 2 Orlistat is associated with gastrointestinal disturbances (e.g., oily diarrhea). 2,4
While regular medical monitoring is an important part of any obesity treatment program, it is especially important when weight-loss medications are included.
This content is reviewed regularly. Last updated April 28, 2011.
Other Science Library Topics:
1Identification, Evaluation, and Treatment of Overweight and Obesity in Adults NIH/NHLBI
2Weight-control Information Network. Prescription Medications for the Treatment of Obesity.
3Halford JC. Clinical pharmacotherapy for obesity: current drugs and those in advanced development. Curr Drug Targets. 2004 Oct;5(7):637-46
4Padwal R, Li SK, Lau DC. Long-term pharmacotherapy-term pharmacotherapy for obesity and overweight. Cochrane Database Syst Rev. 2004;(3):CD004094.