Public Citizen Group has filed a petition, Monday, with Food and Drug Administration asking health officials to ban the prescription version of fat-blocking drug orlistat, citing a link to what some scientists believe are precancerous lesions in the large intestine.

The petition asks for the removal of the drug from the market, sold by Roche since 1999 under the brand name Xenical.

Dr. Sidney Wolfe, director of Public Citizen's Health Research Group, said scientific studies in rats linked orlistat to increased numbers in the colon of aberrant crypt foci, or microscopic lesions that some experts think are precancerous.

The petition came just days after the regulatory agency gave conditional approval to GlaxoSmithKline to sell a nonprescription version of the drug.