The Food and Drug Administration (FDA) is conducting investigations following the reports of liver damage in patients who are on diet pills, which contain the chemical Orlistat, an ingredient in the widely used over-the-counter drug Alli, and its prescription version Xenical.

The FDA has not yet sent out any public warnings against the use of the drug but it is investigating the 32 cases, which have been reported with serious liver damage from the year 1999 to 2008. These include six cases of liver failure and two that occurred outside the United States.

Orlistat inhibits the intestines from absorbing fat when consumed thrice a day with meals. The prescription drug Xenical had been approved by the FDA for weight management in a synchronized manner with reduced calorie diet Alli, which is almost half the dose of Orlistat was given a go-ahead for use in 2007.

"We estimate that since 1999, more than 11 million prescriptions have been dispensed, and we see 32 adverse events around the world. It's a fairly unusual occurrence [for a] very popular drug," an FDA spokeswoman said.

GlaxoSmithKline, the British drugmaker, is marketing both the drugs- Alli and Orlistat. Although Xenical is manufactured by Swiss firm - Roche.

FDA suggested the patients to continue the use of diet pills until they notice symptoms such as weakness, fever, jaundice and other signs of liver injury.