Adipex and Xenical are brand names for popular prescription diet pills. The stimulant phentermine, which suppresses appetite, is the primary ingredient in Adipex. The fat-blocking agent orlistat comprises Xenical. While both diet pills are generally safe, some patients are at risk for adverse and even life-threatening side effects, especially when the prescriptions are not used as directed, warns PubMed Health.
The Fen/Phen Combo
The Food and Drug Administration banned the combination of phentermine with fenfluramine in 1997. A number of patients experienced serious and sometimes fatal heart valve and lung damage. But phentermine is generally safe when used alone, though patients should not use the drug for more than 12 weeks.
Xenical and Liver Injury
In 2009, the Food and Drug Administration started investigating claims that Xenical and its over-the-counter dosage Alli cause potentially serious liver injury. As of 2011, both drugs are still available to people throughout the United States. Signs that orlistat has caused liver injury in a patient include jaundice and dark-colored urine.
Phentermine Side Effects
Phentermine, whether in its generic form or branded as Adipex, causes sleeplessness, nervousness and increased heart rate in some patients, warns the Mayo Clinic. Blurred vision and constipation are also potential side effects. Patients can decrease their risk of unpleasant side effects by using the pills only as directed, for a short period of time, and by not mixing the medication with other diet drugs or pills designed to combat high blood pressure.
Xenical Side Effects
The most commonly reported side effects associated with Xenical use involve problems with bowel movements, according to PubMed Health. People who eat meals with more than 15 g of fat experience the most risk of uncontrollable bowel movements, loose stools and oily spotting on the underwear. Some patients may experience stomachaches, rectal pain and irregular menstrual periods.
Additional Considerations
People who use diet drugs such as Xenical usually lose only about an additional 5 to 7 lbs. per year than they would have with just diet and exercise, according to the Mayo Clinic. Also, when people stop taking diet pills such as phentermine and Xenical, they tend to regain any weight lost. No diet pill will work without consistent exercise and dedication to a low-fat, healthful eating plan. The Food and Drug Administration has approved the use of Xenical for up to two years; some patients use the drug for longer periods of time, but its long-term safety is still being studied.
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