WASHINGTON -- The drugmaker working to develop a pill to boost sexual desire in women says regulators are demanding more studies on the experimental pill.

Sprout Pharmaceuticals said Tuesday the Food and Drug Administration wants to see more data on how the company's drug, flibanserin, interacts with other medications and how it affects driving ability. Nearly 10 percent of women studied in company trials reported sleepiness while taking the daily pill.

The FDA's request represents another hurdle in the pharmaceutical industry's 15-year search for a female equivalent to Viagra.

But Sprout Pharmaceuticals President Cindy Whitehead described the development as a "significant step" toward the drug's approval. The three studies requested by the FDA are relatively small, involving 25 to 50 patients each. The company did not give a timeframe for completion.