UPDATE: Biogen Shares Sink as Cowen Warns of 'Double-Counting' on Tecifera Prescriptions

In a report on Biogen BIIB published Tuesday, Cowen Group analyst Eric Schmidt suggested weekly prescription data report from IMS Health might contain some double-counting on Tecifera prescriptions. Schmidt believes the number of new patients using Tecfidera prescription could have been overestimated by as much as 36 percent amid an IMS practice which records prescription as new prescriptions data (NRx) when any part of the prescription changes. Cowen maintains an Outperform rating and $278 price target on shares of Biogen. Traders in Biogen seem to be responding to the concern Tuesday afternoon; the stock is down 2.9 percent to $220.84.