Xenical is a prescription weight loss drug by Roche Laboratories while Alli is an over-the-counter weight loss drug made by GlaxoSmithKline. The active ingredient in both drugs is orlistat, which blocks the absorption of fats in the intestines.
A cause-and-effect relationship between the drugs and liver injury is yet to be established but the agency feels the public should be warned because the condition is serious.
The FDA reviewed 12 cases of severe liver damage in patients outside the U.S. who took Xenical and one patient in the U.S. who took Alli. Two died and three needed liver transplants.
Roche and Glaxo have agreed to add the information about liver damage to the precautions listed on the medication label.
Patients are urged to watch for signs and symptoms of liver injury which can include weakness, itching, yellow eyes and skin, dark urine and loss of appetite.
In 2006, Public Citizen petitioned the FDA to remove Xenical from the market because of its link to the risk of aberrant crypt foci, a possible precursor to colon cancer.
An estimated 40 million people worldwide have taken Xenical or Alli, the FDA said.