(pharmacology) A drug that is used in the form of its citrate C₂₂H₃₀N₆O₄S·C₆H₈O₇ to treat erectile dysfunction in males, that by suppressing a phosphodiesterase enzyme also suppresses the enzyme's inhibitory effect on the hormone cyclic GMP, and that enables the cyclic GMP produced during sexual arousal to initiate the muscular and vascular changes which produce an erection. It is marketed under the trademarks Revatio and Viagra.

(pharmacology) The citrate salt of sildenafil, marketed as Viagra, a treatment for erectile dysfunction