The Food and Drug Administration alerted doctors Thursday that Viagra and other drugs used to treat impotence have been linked to sudden hearing loss. The FDA has announced it will add a warning to the drugs about the risk.

The agency has counted 29 reports of hearing problems since 1996. Cialis and Levitra are also among the drugs to bear the warning, as will the hypertension drug Revatio.

Hearing loss reportedly occurred within hours to two days of taking the drugs, though it's unclear what causes it. A third of the cases were temporary and reports also involve hearing loss in one ear.