Two popular weight loss pills will soon include warnings about possible severe liver damage. Alli, sold over-the-counter by GlaxoSmithKline, and the prescription version Xenical, manufactured by Roche, both use the same active ingredient, orlistat. The cases of liver damage are extremely rare. The Food and Drug Administration found 13 cases in which people taking orlistat suffered severe liver damage; 12 were outside the United States. The FDA also said that it is not clear orlistat caused the damage.

Alli has been used by more than 10 million people since its 2007 debut, the Associated Press reports. Xenical launched in 1999 and has been used by more than 36 million people.