How the drug Viagra works

Viagra, medically know as sildenafil citrate, is a drug widely used to treat erectile dysfunction. You need to know the physiology of erection  to understand the way it works in people with erectile dysfunction. Penis is made of smooth muscles, arteries and veins. These three components play major roles in erection of the penis. In flaccid phase, the smooth muscle cells situated within the walls of the blood vessels are in a contracted state. This causes constriction of the vessels. Constricted vessels only allows small amount of blood to the penis.  When the male gets sexually stimulated, the brain sends down the impulses which cause the release of neurotransmitters. These neurotransmitters cause relaxation of the smooth muscles. 

The chemical they release is nitric . Nitric oxide is a potent vasodilator. It has the ability to stimulate the enzyme guanylate sulfate. This enzyme produces another chemical called cGMP. Finally, cGMP is the chemical responsible for the smooth muscle relaxation. As a result, the diameter of the blood vessels increases. So, more blood can come to penis with minimum resistant. The blood accumulates within the sinusoids of the penis. Meanwhile, the venous outflow also gets blocked.  This leads to erection of . Then the ischiocavernosus muscle contracts. This phase is called rigid erection phase. Men develop erectile dysfunction when these steps don’t occur properly. cGMP is removed from the system by the action of another chemical called phosphodiesterase 5.

As described above, smooth muscle cells are the ones which determine erection. If the smooth muscle cells fail to relax, the person finds it difficult to have an erection. As described earlier, cGMP should be there to cause erection. People with erectile dysfunction lack this chemical. Viagra has the ability to cause smooth muscle cell relaxation when the person is sexually aroused.  Its does this by inhibiting the enzyme phosphodiesterase which is responsible for the degradation of cGMP. As a result, more cGMP accumulates and more erection is achieved. The effect of Viagra is limited to penis. This is because the penis is the only place where there is phosphodiesterase 5.

Like in any drug, Viagra also has its own side effect profile. Commonest side effects men complain are alteration of the green and blue color perception, headache, long lasting painful erection and dependency. It can also have very serious side effects such as heart attacks. That is why Viagra is not an over the counter drug. Viagra is not given to people taking nitroglycerine for angina. Nitroglycerine also causes vasodilatation by increasing the amount of nitric oxide. The effects get exaggerated if you take both of them together.

Viagra (Sildenafil) is also used to treat pulmonary hypertension . This is a new development in the field of Medicine. Viagra is marketed as Revatio for the treatment of pulmonary hypertension. Its action is also used to relieve mountain sickness, Raynaud’s phenomenon and heart disease.