Viagra (Sildenafil Citrate)

How do Viagra, Cialis and Levitra work?

Viagra, Cialis and Levitra have absolutely the same mechanism of action and all belong to selective inhibitors of the enzyme phosphodiesterase-5-type (PDE-5). This enzyme in turn inhibits the production of cyclic guanosine monophosphate (cGMP) in the smooth muscle tissue, which is formed from the guanosine-monophosphate (GMP) under the action of nitric oxide (NO). The main function of cGMP is the relaxation of smooth muscles of corpus cavernosum of the penis. When the action of PDE-5 is inhibited, the cavernous bodies accumulate a much larger amount of cGMP, their smooth muscle is better relaxed and blood flow to the penis becomes significantly larger that causes an erection.

Medicines of this group act selectively in the vascular tissue of the penis and are virtually harmless. They do not cause persistent adverse effects in long term and regular use. The erectile dysfunction pills do not cause addiction. However, it is obvious - once you try the pill for erectile dysfunction and feeling a much better quality of erection, it is very unporbably a man will give up on Viagra, Cialis or Levitra.

The main advantage of PDE-5 inhibitors is that they do not cause erection at inappropriate times because they act only in response to sexual stimulation. If there is no sexual stimulation, there is no erection. All three drugs - Viagra, Cialis, Levitra - are taken orally before the planned sexual activity, and their action is based on increased blood flow to the penis in response to sexual stimulation.

Differences between Viagra, Cialis and Levitra are not big Levitra has fewer side effects compared to Viagra and its effect lasts for about the same time as Viagra. Cialis has few side effects and its action is longer.