Viagra contains sildenafil citrate, a selective PDE5 inhibitor. Sildenafil works by enhancing the nitric-oxide-mediated blood-flow response in penile tissue when sexual stimulation occurs.

It is used for erectile dysfunction and does not independently produce sexual desire or an erection without stimulation. The supplied product specifies a 25mg tablet presentation.

Sildenafil can interact with nitrate medicines and certain cardiovascular treatments. Common adverse effects can include headache, flushing, nasal congestion, indigestion, and visual disturbances.