The European Medicines Agency has started a review of the weight loss drug orlistat, marketed under prescription by Roche as Xenical and sold over the counter by GlaxoSmithKline as Alli to see whether "very rare cases of hepatic injury have an impact on their benefit-risk profile".

The EMA says that "the risk of liver reactions with orlistat is well known" and had been kept under close review by the agency’s Committee for Medicinal Products for Human Use (CHMP) since the initial marketing authorisation of these medicines. The risk is already included in the product information for orlistat-containing drugs.

However, the new review is based on the most recently-submitted analysis, which covers of cases of hepatic events reported with Xenical between August 2009 and the end of January 2011. Some 21 suspected cases have been identified, of which four were cases of severe liver toxicity. The EMA notes that the number of cases "needs to be considered in the context of cumulative usage of these medicines in 38 million patients".

During the period between May 2007 and January 2011 there were a total of nine reports of suspected severe liver injury with Alli, although in some cases "other possible explanations for liver injury were present and some cases provided insufficient information to allow assessment". About 11 million patients have taken Alli, a product that GSK is looking to divest.

Both Xenical and Alli had their labels changed by the US Food and Drug Administration in May 2010 to include safety information about cases of severe liver injury that have been reported rarely with its use.