UPDATE 4-Transcept Pharma sleep drug denied approval, shrs sink

* FDA asks for more data citing safety issues

* Co says may need to conduct additional safety trials

* CEO: Enough cash to see through required trials

* Says hopes FDA meeting will not need more than a yr

* Shares fall as much as 50 pct (Adds CEO comments, updates stock movement)

By Esha Dey

BANGALORE, Oct 29 (Reuters) - Transcept Pharmaceuticals Inc (TSPT.O: Quote, Profile, Research) said U.S. health regulators did not approve its experimental sleep-disorder drug, citing safety issues, and requested additional data that might require more studies, wiping out half the company's market value.

The U.S. Food and Drug Administration has asked for additional data to show that the drug Intermezzo, when taken in the middle of the night as directed, would not present any risk, particularly related to driving ability on the next day.

Transcept is trying to get the drug approved for use as-needed to treat insomnia in patients who find it difficult to return to sleep after waking up in the middle of the night.