•  Impotence: Causes and Treatment

Manufacturer : Pfizer (no generics)

Looks like : Small blue diamond-shaped pills

Available dosages : 25 milligrams, 50 mg, 100 mg

As you've probably heard, Viagra (sildenafil) is used to treat erectile dysfunction (commonly called "impotence") in men who either can't have or can't maintain erections. On the market since March 1998, it's one of the most commercially successful drugs ever launched, with millions of prescriptions filled at a cost of more than $ 1 billion during the first year alone. It even has the blessing of the Vatican, on the ground that it can strengthen families.

Just as important, here's what Viagra can't do. It isn't an aphrodisiac; it can't get you aroused when you're not interested. And it's not a performance-enhancer. If you're healthy, Viagra won't give you a faster or harder erection or help you last longer. In fact, in healthy men it can even cause a painful, long-lasting erection (a condition called priapism) that may lead to erectile dysfunction if it isn't treated quickly.

Viagra works for about 70 to 85 percent of men with erectile dysfunction caused by physical factors, such as damaged nerves (a frequent effect of diabetes), narrowed blood vessels (an effect of atherosclerosis), or side effects from medications. It can also help men whose erectile dysfunction stems from anxiety or other psychological causes.

Two studies reported at a meeting of the American Urological Association in San Francisco suggest that Viagra may offer long-term help for some prostate cancer patients and other men suffering from erectile dysfunction. Researchers at Rush University Medical Center in Chicago gave nightly doses of Viagra to 54 men who had their prostates removed, but surrounding nerves left intact. About 90 percent of men who have this type of surgery are unable to obtain erections afterwards. However, almost a third of the men who took Viagra before going to sleep every night recovered erectile function after 9 months. Researchers theorize that when taken at bedtime, the Viagra allowed the men to resume having erections during sleep, something that is necessary for normal sexual functioning.

A second study at the University Medical Center in Cologne, Germany supports these findings. Seventy-six men who had been impotent for 6 months were given nightly doses of Viagra or used Viagra only when they wanted to have sex. After a year, 60 percent of the men who took the drug every night recovered full sexual function, compared to only 9.7 percent of those who took Viagra only when they wanted to.

These are small, preliminary studies, however, and further research is needed to find out whether these results are reliable. In the meantime, you should only take Viagra according to your doctor's instructions.

You usually swallow one tablet about an hour before sex. It takes an hour to take peak effect, though the waiting time can range from half an hour to two hours. The process doesn't begin automatically, though -- you still need to be aroused in order to have an erection. Viagra starts clearing out of the bloodstream about two hours after you take it, and it's mostly gone after six hours or so.

Normally, this is what happens when a man is aroused: A chemical called cyclic GMP triggers a chain of reactions that end up relaxing the penis muscles and letting extra blood flow in (rigid muscles don't cause the hardness of an erection; the extra blood does).

Viagra boosts the levels of cyclic GMP in the penis. It does this by preventing an enzyme (a protein involved in a biochemical reaction) called phosphodiesterase type 5, or PDE5, from breaking down cyclic GMP as fast as it usually does. The result: Cyclic GMP stays around longer, the muscles relax, and more blood flows in and stays in.

The most serious side effect of Viagra results from a possible drug interaction. Taking Viagra while you're on any drug that contains nitrates, such as a common type of heart medication called nitroglycerin (the same chemical as dynamite, sold under many brand names including Nitrostat, Transderm-Nitro, Nitrolingual, and Nitrogyn), can cause a sharp and sometimes fatal drop in blood pressure. Talk to your doctor or pharmacist to make sure Viagra won't interact harmfully with anything else you're taking.

Even if you're not on nitroglycerin, Viagra's new label advises doctors to use caution in prescribing the drug to anyone with a history of cardiovascular disease, including heart attack, stroke, angina, or high or low blood pressure. That's because if you should ever suddenly need to take nitroglycerin, the chance of an interaction with Viagra could be too great to risk. To date, at least 130 men have died shortly after taking Viagra. In most cases they had heart attacks, although it isn't clear whether those were caused by Viagra or by the excitement and exertion of having sex after a long break.

Other side effects are related to the way Viagra works in the body. The enzyme blocked by Viagra, PDE5, is also found in other parts of the body, among them the blood cells known as platelets and some muscles around blood vessels. The drug can disrupt the way blood cells and vessels normally function in certain areas, including the head, skin, and stomach -- which might explain many of its commonly reported side effects, such as headache (reported by 16 percent of users), flushed skin (10 percent), and indigestion (7 percent).

Viagra blocks PDE5 very well, but it can also partly block a closely related enzyme, PDE6, which is found in the retina of the eye. That's why about 3 percent of men on Viagra experience visual side effects, including bluish or blurry vision and sensitivity to light. In July 2005, the FDA issued an alert that a small number of men lost eyesight in one eye some time after taking Viagra, Cialis, or Levitra. Doctors don't know whether the drugs caused the vision loss, but people with certain conditions -- like heart disease, diabetes, hypertension -- are at higher risk of developing the complication. Similarly, men with existing eye conditions -- like retinitis pigmentosa, for example -- may need to steer clear of the drug altogether to avoid eye damage.

Most recently, the FDA reported that Viagra, Cialis, and Levitra may also cause sudden hearing loss. While hearing loss is a common malady among older people, and the FDA found only 29 cases of sudden hearing loss related to these drugs, the agency emphasizes that "sudden hearing loss is an uncommon event at any age."

So far there's no evidence that it can help women who have sexual problems. A small study of postmenopausal women on Viagra found that the drug did increase blood flow to the clitoris (often uncomfortably so) but didn't help any of the women get aroused more easily or feel more pleasure during sex.

If you think you need the little blue pills, you probably have a health problem already -- so it's important to discuss things with your doctor in order to make sure Viagra can actually help you without harming you. The drug is approved for sale in the US, Japan, and Europe, and is legally available by prescription only. You'll need to check with your health plan to find out whether it's covered; at about $20 a pill, it's pretty pricey.

Some Web sites sell Viagra illegally without a prescription, but it's NOT a good idea to order from them. There's no guarantee that you'll get the genuine article, you'll pay much more, and your medical history won't be reviewed properly, if at all.

Viagra isn't the first -- or the only -- game in town. Two additional drugs that work much like Viagra have been approved by the FDA: Levitra (vardenafil) and Cialis (tadalafil). Until these pills came along, the most common drug treatment for erectile dysfunction consisted of injecting alprostadil (a synthetic form of a naturally-occurring chemical called prostaglandin E1) into the penis. For obvious reasons, that never caught on the way Viagra has. Prostaglandin E1 works much like Viagra, relaxing muscles and dilating blood vessels.

Another prescription medication, Regitine (it's generic name is phentolamine) is also an erectile dysfunction drug that's injected into the penis. A pill form called Vasomax will soon be available, although it's less effective than injections. Just as Viagra does, phentolamine enhances the flow of blood to the penis to produce an erection, but unlike Viagra, it doesn't interfere with nitrate medicines and could be safer for men with heart disease.

Some herbal preparations, often containing yohimbe, are sold under names like "Viegra" and "Viagre," but these are not related to the real Viagra. Yohimbe is the bark of an African tree, fabled as a sexual stimulant in men and women. Like Viagra, the bark's active ingredient (called yohimbine) increases blood flow to the penis, but it hasn't shown consistent results in clinical studies of erectile dysfunction. Yohimbine is also available in prescription pill form, under the name Yocon. This purified form of yohimbine has fewer side effects than the raw bark, which can dangerously increase blood pressure and heart rate. However, it's important to note that the American Urologic Association does not recommend yohimbine for the treatment of erectile dysfunction.

References

First published August 9, 1999
Last updated December 22, 2008
Copyright © 1999 Consumer Health Interactive

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