What is Viagra made of?
The main ingredient of Viagra is Sildenafil Nitrate; it acts by slowing down cGMP specific phosphodiesterase
type 5 which is an enzyme that is responsible for the chemical reaction to occur which determines when to relax the corpora cavernosa muscle for regulating the blood flow. Now what Sildenafil does is that it hold back this enzyme responsible for regulating the blood flow; therefore when the blood accumulates inside the penis the chemical reaction responsible to cause this enzyme cGMP specific phosphodiesterase type 5 to contract the muscle and stop the inflow which eventually leads to the outflow of blood from the penis and thus the erection is lost, it is not allowed to occur and thus the erection is sustained but at the cost of holding back the blood necessary for the other human organs to function.
Robert F. Furchgott won the Nobel Prize in Physiology or Medicine in 1998 for his discovery and analysis of endothelium-derived relaxing factor (the inhibition of cGMP specific phosphodiesterase type 5 enzyme), a key part of the Sildenafil Nitrate mechanism of action.