flickr.com/Felixe

flickr.com/Felixe

The U.S. National Institutes of Health stopped a trial of the impotence drug sildenafil on Tuesday, saying it caused serious medical problems in sickle cell patients.

The trial was looking at the safety and effectiveness of sildenafil, sold by Pfizer Inc under the brand name Viagra, for pulmonary hypertension in patients with sickle cell disease, the National Heart, Lung, and Blood Institute said.