Shares of Eli Lilly and Co. went soft Wednesday morning after a rival reported its experimental impotence medicine worked faster than Lilly’s Cialis and Pfizer Inc.’s Viagra.

Vivus Inc., a biotechnology firm based in Mountain View, Calif., reported that its anti-impotence pill Avanafil helped men achieve erections in as little as 30 minutes, according to Bloomberg News. That’s twice as fast the median time for Viagra users and four times as fast as the median time for Cialis patients.

The news dampened the mood for Lilly investors, and the company’s share price fell by about 1 percent, to as low as $35.53 in morning trading.

Cialis has become a blockbuster drug for Indianapolis-based Lilly. Through the first nine months this year, the drug racked up sales of $1.1 billion, a 4-percent increase over the same period last year.

Cialis owns about 40 percent of the erectile-dysfunction market, compared with 50 percent for the iconic Viagra, according to Bloomberg. Even though Cialis takes effect more slowly, Lilly has successfully emphasized that its effects last about 36 hours, compared to about four hours for Viagra.

Pfizer’s stock price dipped a bit after markets opened today, but then sprang back into positive territory.

Vivus’ late-stage trial involved only 646 patients who had been struggling to achieve erections, Bloomberg reported. Men taking higher doses of the drug were able to achieve erections sufficient to have sexual intercourse 57 percent of the time, compared to only 27 percent of the time for patients taking a placebo.