Eli Lilly and partner Amylin on Friday got the thumbs up from the US Food and Drug Administration for their diabetes drug, exenatide - the first so-called “incretin mimetic”. However, whilst the companies are revelling in their first ever approval for the drug, there was somewhat of a black cloud lurking over the decision.

Shares in Amylin dropped on the news after it was revealed that exenatide was cleared for use solely as an add-on therapy, and that the FDA had decided to issue an approvable letter for its use as stand-alone drug. The firms would now have to provide additional data to secure the monotherapy label which, although it will receive a six-month review, could be some time off.

Meanwhile, a launch is scheduled for June 1 for Byetta – the name exenatide will be marketed under – and Lilly and Amylin say they are planning additional regulatory filings shortly.