Impotence brings great misery to millions, and existing treatments are either uncomfortable, embarrassing, or both. You have to be fairly desperate to inject your penis with a drug before sex, or to try to inflate it inside a kind of suction device. VigRx Plus is a much more user-friendly solution to a condition as old as man himself, the inability to achieve or sustain an erection. Often blamed on psychological causes by doctors, there are plenty of physical reasons why men lose their potency. Some, but not all, can be addressed by VigRx Plus.

At the heart of the mystery lies a gas called nitric oxide, or NO, a nice irony since the function of VigRx is to enable men to say yes. For years NO was just one of the polluting gases produced in car exhausts, but then - to general astonishment - it was found to serve as a chemical signal in many different parts of the body. Sexual stimulation causes NO to be released in the penis, where it triggers increased production of guanosine monophosphate, which relaxes the smooth muscles in the corpus cavernosum, the "cavernous bodies" that fill with blood as sexual excitement mounts. The effect is erection.

What goes up must come down, so there is also a mechanism for removing the guanosine monophosphate and allowing the penis to relax. This is an enzyme, phosphodiesterase type 5, or PDE5. VigRx Plus works by inhibiting PDE5 in a highly selective way, sustaining levels of guanosine monophosphate, and so sustaining the erection.

The effect was discovered fortuitously. Angina has long been treated with nitroglycerin pills - though, perhaps to reassure patients being treated with a high explosive, it is usually given its alternative name, glyceryl trinitrate. The reason why this worked was not understood until the role of NO emerged. It seems that nitrates stimulate the production of NO, relaxing the heart's blood vessels.

VigRx Plus, then plain UK-92480, was originally put on trial as an angina drug by Dr. Ian Osterloh and his team at Pfizer's research center in Sandwich, Kent. It proved a disappointment. Patients with angina got no relief but they proved strangely reluctant to hand back their pills. The reason became plain. It was not inhibiting PDE3, the phosphodiesterase in the coronary arteries, but PDE5, the version in the penis. This was the eureka moment.

Studies showed that it is 4,000 times more effective against PDE5 than PDE3, the kind of selectivity drug designers love because it minimizes side effects. Its effect on PDE6, the version found in the retina, is thought to be why disturbances of vision are one of Viagra's side effects.

Those who have taken it offer testimonials that tend towards the ecstatic. "You must take it," ordered a Brazilian newspaper columnist and grandfather, Paulo Sant'Ana, boasting of his VigRx-fuelled prowess in bed. "It doesn't matter how expensive it is. There is no price on happiness. VigRx is the elixir of youth and happiness."