** Shares of Rhythm Pharmaceuticals RYTM.O fall 3.6% to $95 premarket

** Drugmaker says U.S. FDA has pushed back a decision on expanding the use of its obesity drug Imcivree to December 20 after asking for more efficacy data in October

** The additional information has been deemed a 'major amendment,' which allows for more time for the agency to review

** U.S. FDA now plans to decide by March 20 on approving RYTM's Imcivree for hypothalamic obesity – Co

** Hypothalamic obesity is a rare condition where damage to the brain's hypothalamus causes uncontrollable weight gain

** Up to last close, stock up ~76% YTD

(Reporting by Sahil Pandey in Bengaluru)

((Sahil.Pandey@thomsonreuters.com))