The move comes in the midst of growing controversy over fen-phen (a combination of fenfluramine and phentermine) and dexfenfluramine, marketed as Redux, another popular weight-loss drug.

The suit, filed by two organizations representing obese people and six individuals who claim they have been injured by the drugs, seeks to order the Food and Drug Administration to block sales of Redux nationally and to forbid the combination use of fenfluramine and phentermine. Fenfluramine is marketed as Pondimin; phentermine as Fastin, Adipex-P and Ionamin.

Sales of the drugs totaled an estimated 20.6 million prescriptions last year, according to IMS America, a market research firm. But their use has plummeted over the past few months as reports of potential dangers began to surface, and many dieters ditched them out of fear. Sales of Redux dropped 36% from the first week of July to the last week of August; phentermine sales were down 30% and fenfluramine sales dropped 56%, the research firm says.