The latest drug candidate from sanofi-aventis' (NYSE:SNY) was supposed to help people sleep, but it looks as though it'll be keeping management up at night. Yesterday, the drug company said the Food and Drug Administration had turned down the application to market its insomnia drug, Ciltyri.

The FDA apparently wants "additional information regarding benefit-risk" profile. The company wasn't very forthcoming in its press release, so it remains to be seen whether that means sanofi will need to run an additional trial or whether it will be able to satisfy the agency with data that it already has.

Because insomnia isn't generally a life-threatening illness, and there are plenty of treatment options, it's not surprising that the FDA would be cautious about side effects. Ciltyri, however, seemed to have sufficient efficacy data with no withdrawal symptoms or rebound effect -- having worse insomnia after the treatment is ended -- which can occur with other insomnia drugs, so I imagine sanofi is a little surprised by the FDA's decision.

While it tries to figure out exactly what the FDA needs to approve Ciltyri, sanofi still has Ambien CR to tide it over on the sleepless nights. Among others, it competes with Sepracor's (NASDAQ:SEPR) Lunesta and the regular version of Ambien.

This company really needs a revenue boost, with Plavix contending with rivals from Eli Lilly (NYSE:LLY) and Daiichi Sankyo's Effient, while Lovenox faces generic competition if Novartis (NYSE:NVS) and Momenta Pharmaceuticals (NASDAQ:MNTA), or Teva Pharmaceuticals (NASDAQ:TEVA) and Amphastar Pharmaceuticals, can get their marketing applications approved. Until then, it looks like more sleepless nights for Sanofi.

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Fool contributor Brian Orelli, Ph.D., doesn't own shares of any company mentioned in this article. The Fool has a disclosure policy.