Cephalon's (CEPH. O) sleep disorder drug Nuvigil as a treatment for jet lag has not been approved by the U. S. health regulators. This step has questioned the quality of some of the data used to seek approval. Following this the drug maker's shares fell nearly 5 per cent.

Cephalon's flagship sleep disorder drug Provigil's follow-up Nuvigil, is believed to treat narcolepsy, sleep apnea, and shift work sleep disorder.

The drug's label to include approval to treat excessive sleepiness associated with jet lag resulting from eastbound travel was being seeked by the company. A complete response letter was sent to Cephlon that indicated that the agency would not approve the drug for jet lag at this time instead of a final decision from the U. S. Food and Drug Administration (FDA).

Cephalon's Chief Medical Officer Lesley Russell said, "Although we reached statistical significance on both primary endpoints, the Complete Response letter raised questions regarding the robustness of the PGI-S data (Patient Global Impression of Severity). We have already reviewed this issue with the FDA and will be scheduling a meeting with the agency in the near future to discuss it further."

It was however not indicated that how long an approval for the jet lag indication might take.