By David Jay Brown

Some people claim that Viagra has made more people happy than any other drug in human history.

Before Viagra, men with erectile difficulties had to endure some pretty extreme pharmacological measures in order to obtain erections. For example, some men with erectile dysfunction used to inject a drug called Paperverine directly into their penis in order to obtain erections. Perhaps equally unattractive was a method of depositing suppositories of a drug called alprostadil directly into the urethra of the penis. Although both of these treatments for producing erections are quite reliable (around 77%), the pain and complications involved make them unattractive to most men with impotency problems.

This is why, for men with erectile difficulties, Viagra (or sildenafil citrate) was such a huge advance. According to the Physician's Desk Reference, 82% of men report an improvement in their erections after simply swallowing 100 milligrams of Viagra--which explains why Viagra is one of the most popular pharmaceutical drugs in the world. Since it first became available from Pfizer in 1998, Viagra has been used by more than 16 million men around the world. According to Phizer's web site, 9 tablets of Viagra are dispensed every second worldwide.

Viagra works by enhancing the effect of Nitric Oxide, the only known gaseous neurotransmitter (or chemical messenger in the brain). Nitric Oxide is the primary neurotransmitter responsible for causing erections in men.

It works like this. Inside the human penis are paired erectile chambers running almost the entire length of the organ called the Corpora Cavernosa. These chambers are filled with spongy tissue, rich in tiny pool-shaped blood vessels, which are surrounded by smooth muscles that play a key role in initiating an erection.

Paradoxically, the muscles must relax for an erection to occur. This allows blood to flow into the penis, and for the corpora cavernosa to inflate. The chemical messenger that allows this to occur is Nitric Oxide, which Viagra enhances the effect of, and thus increases blood flow to the penis. Viagra can accomplish this in as quickly as 30 minutes, and it generally lasts for around 4 hours. This doesn't mean that one will have an erection for 4 hours, but rather that, with the proper stimulation and arousal, for a 4 hour period, most men won't have any difficulty achieving a solid erection.

Many men with erectile difficulties say that Viagra changed their lives. Even some men who don't really have a serious problem with impotence say that they use Viagra as a kind of "insurance", so that they don't have to worry about whether or not they'll be able to perform.

Viagra is a prescription drug in the United States, and it doesn't work for everyone, such as people with serious organic problems. Also, for people with weak cardiovascular systems, Viagra can have dangerous side effects, so it is important to consult with a physician about your concerns. According to the Pfizer Web site the most common side effects of Viagra are headache, facial flushing, and upset stomach. Also, but less commonly, other side effects may include bluish vision, blurred vision, or sensitivity to light.

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