Viagra is undoubtedly the world's best-known treatment of impotence

Chemically, it is Sildenafil citrate, while Viagra is its most famous brand name.

Viagra are diamond-shaped and blue in color, with the word 'Pfizer' on one side, and 'VGR 25', 'VGR 50', or 'VGR 100' on the other side, the figures indicating the dose of the pill in milligrams. Regardless of dose, each Viagra pill costs approximately $10.

How it acts

Viagra falls within the drug category called phosphodiesterase (PDE) inhibitors. In order to understand how Viagra acts the human body, let's first try to grasp how natural sexual stimulation happens.

Parasympathetic nervous system causes the release of nitric oxide (NO) in the penis. NO binds itself to receptors of a certain enzyme, which leads to increased levels of a monophosphate called cGMP. This monophosphate relaxes muscles of the penis and dilates blood vessels, resulting in increased flow of blood into the penis, thus causing erection.

Erectile dysfunction, i.e., impotence, is caused by degradation of cGMP by something called PDE5. Since Sildenafil (the therapeutic component in Viagra) has a molecular structure similar to cGMP, it has the same effect of cGMP on the muscles and blood vessels of the penis.

Thus, despite the degraded condition of natural cGMP in the penis, the organ is 'fooled' into believing that a lot of cGMP is present, though in reality it is the molecularly similar Sildenafil, or Viagra.

Dosage

Viagra is a prescription drug and therefore must not be used independently of medical advice.

Whatever the dose the physician prescribed (25mg, 50mg, or 100mg), it must not be taken more than once a day between 30 minutes and four hours before sexual intercourse.

Caution

Viagra must not be used by patients with severe liver or renal impairment, low blood pressure, hereditary degenerative retinal disorders, recent heart attack, and men for whom sexual intercourse is inadvisable due to heart problems.

Other uses

Incidentally and interestingly, when Pfizer (the manufacturer of Viagra) started research into the medicine, they were looking for a drug to treat heart problems. But, as research progressed, it was found to be more effective in the treatment of impotence.

Nevertheless, Viagra does find application in treatment of a heart problem called pulmonary arterial hypertension, or Revatio. For this treatment, the dosage is usually one 20mg pill three times a day.

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