To ensure you’re getting the best results from sildenafil, you should make sure that you’re using it correctly and safely. Below we have detailed the answers to some of the most commonly asked questions about taking sildenafil correctly. Sildenafil tablets, USP, an oral therapy for erectile dysfunction, is the citrate salt of sildenafil, a selective inhibitor of cyclic guanosine monophosphate (cGMP)-specific phosphodiesterase type 5 (PDE5). Sildenafil tablets, USP, an oral therapy for erectile dysfunction, is the citrate salt of sildenafil, a selective inhibitor of cyclic guanosine monophosphate (cGMP)-specific phosphodiesterase type 5 (PDE5). Know what Sildenafil is used for, how to take it, and which side effects to expect when starting it. Sildenafil works by blocking an enzyme in the body called PDE5, which helps relax certain blood vessels. For erectile dysfunction, it increases blood flow to the penis when aroused. Sildenafil is used to treat erectile dysfunction (also called sexual impotence). Sildenafil belongs to a group of medicines called phosphodiesterase 5 (PDE5) inhibitors. VIAGRA (sildenafil citrate), an oral therapy for erectile dysfunction, is the citrate salt of sildenafil, a selective inhibitor of cyclic guanosine monophosphate (cGMP)-specific. Sildenafil is used to treat erectile dysfunction in adult men or pulmonary arterial hypertension in adults and children, depending on the brand or formulation. Includes sildenafil side effects, interactions, and indications. Sildenafil is in a class of medications called phosphodiesterase (PDE) inhibitors. Sildenafil treats erectile dysfunction by increasing blood flow to the penis during sexual stimulation. Viagra is a prescription medicine used to treat the symptoms of erectile dysfunction. Learning about dosages, side effects, drug interactions, warnings, and more.