Sildenafil, the active ingredient in Viagra

Sildenafil is the active ingredient in Viagra tablets, a medicine used in the treatment of erectile dysfunction (impotence). An erection involves signals from the nervous system and the release of chemical messengers within the tissues of the penis. One of these chemical messengers is called cyclic GMP which causes widening of the blood vessels allowing more blood to flow to the penis Cyclic GMP is normally broken down by the chemical phosphodiesterase type 5 and sildenafil prevents the action of this chemical and inhibits the breakdown of cyclic GMP. Blood vessels are dilated for longer, improving blood flow to the penis and maintaining an erection. The large group of crystals in the centre are 100 micrometres in diameter.