The Food and Drug Administration said Wednesday it has added a warning about the risk to the label of the drug alli, which is sold over-the-counter by GlaxoSmithKline. The prescription version Xenical is manufactured and marketed by Roche.
The FDA identified 13 instances of liver damage associated with the drugs. A causal effect between the drugs and the problem has not been established.
The FDA urged doctors and patients to watch for signs of liver injury, including itching, yellow eyes and skin and loss of appetite.
Glaxo said in a statement it is "committed to ensuring that consumers and physicians understand the safety profile" of alli. More than 10 million people worldwide have used alli since it was launched, according to Glaxo.
Roche said the "safety profile of Xenical is based on more than 10 years of clinical experience and more than 36 million patients worldwide have received Xenical."
The FDA first approved Xenical in 1999 and alli in 2007.
U.S. sales of alli more than doubled last year to $293 million, though they have come nowhere near the blockbuster numbers originally expected by Wall Street after the drug's 2007 launch. Analysts say the brand has been hurt by lower consumer spending as well as unpleasant side effects, such as anal leakage.
GlaxoSmithKline, based in London, is one of the world's largest drug companies.
The FDA first requested information from Glaxo about liver toxicity nearly two years ago.
