An experimental impotence drug being developed by Vivus Inc. showed promise in promoting sex in a mid-stage clinical trial, the company said on Thursday, pushing shares up 12 percent in premarket trading.

Vivus said a study of 284 patients took either a placebo or the compound, avanafil, for 12 weeks at varying doses. Among those taking the highest dose of the drug, 64 percent had erections long enough for intercourse, the company said.

The company did not give a comparison figure for those taking the placebo.

Mountain View, California-based Vivus said patients taking avanafil did not show any signs of visual disturbances.

U.S. regulators last month reported 40 cases of Blindness in men taking several impotence drugs including Pfizer Inc.‘s Viagra.

Vivus said the most common side effect among patients taking avanafil was headache.

Shares were bid at $3.74 in premarket trading, after closing at $3.34 on the Nasdaq on Wednesday.

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