Sildenafil is primarily utilized to address male erectile dysfunction. It blocks phosphodiesterase 5 (PDE5), a naturally occurring enzyme responsible for denaturing cGMP, which is a molecule that regulates penile blood flow. By stimulating the relaxation of the blood vessels in the penis, Sildenafil allows more blood to flow into the area, resulting in an erection.

Sildenafil is also sometimes used to treat pulmonary arterial hypertension (PAH). It helps relax the blood vessels in the lungs, reducing blood pressure and improving exercise capacity in individuals with PAH.

There is also research involving men with ED and another in men with type 2 diabetes that suggest Sildenafil increases testosterone.