Viagra (sildenafil) in 25, 50 or 100mg doses and tablets was originally approved for Erectile Dysfunction.
Revatio (sildenafil) was approved in a 20mg tablet for the treatment of pulmonary arterial hypertension.
Today, both are available generically, and 20mg sildenafil tabs are often cheaper than Viagra. Taking five 20mg tablets can be cheaper than a 100mg Viagra tablet/dose, for example, but with the same effect. 20mg sildenafil is sometimes prescribed “off label” if a doctor deems it medically appropriate.