Previous studies have shown that sildanafil, the active ingredient in Viagra, is effective at treating pulmonary hypertension in otherwise healthy patients

Manufacturers Pfizer sell it in the US under the brand name ‘Revatio’. Viagra relaxes the blood vessels and so helps to prevent the build up of high blood pressure that can cause heart attacks and even death.

The National Heart, Lung and Blood Institute had hoped that Viagra could work with sickle cell patients as well, about 30% of whom suffer from pulmonary hypertension.

This is due to the damage the disease causes to the lining of the blood vessels running between the heart and lungs.

However though the initial clinical trial was meant to go on for a year, it was stopped after 16 weeks after it was discovered that the patients were significantly more likely to experience a painful sickle cell crisis. Of the 33 patients, 38% taking the medication had crises, compared to 8% taking the placebo.

The researchers said that as the trial was specific to sickle-cell patients, there was no risk to otherwise healthy people taking Revatio. However there has been surprise at the results, as Revatio has generally been successful and theoretically should have worked. The researchers are still unsure as to why it increased the likelihood of a sickle cell attack.

For more news stories about Viagra please CLICK HERE.