By Deepi Brar
CONSUMER HEALTH INTERACTIVE

Note: This article has been localised for an Irish audience. >

Manufacturer: Pfizer (no generics) Looks like: Small blue diamond-shaped pills

As you've probably heard, Viagra is used to treat impotence in men who either can't have or can't maintain erections. In Ireland, Viagra is available on prescription only. 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 impotence if it isn't treated quickly.

Viagra works for about 70 to 85 percent of men with impotence 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 impotence stems from anxiety or other psychological causes.

Unfortunately, it isn't very useful to men who have severe impotence produced by advanced nerve or blood vessel damage, or men who've had radical prostatectomies (prostate removals) even when the surrounding nerves were spared during surgery.

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 Angised, Transiderm-Nitro and Nitrolingual spray), or amyl nitrite ('poppers'), 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 in the US, 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, flushed skin, and indigestion.

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 a small percentage of US men on Viagra experience visual side effects, including bluish or blurry vision and sensitivity to light. Men with retinitis pigmentosa may need to steer clear of the drug altogether to avoid eye damage.

So far there's no evidence that it can help women who have sexual problems. A small study of postmenopausal women on Viagra in the US 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 available by prescription only in Ireland.

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. Until it came along, the most common drug treatment 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. Anti-impotence drugs available on prescription in Ireland include Caverject, an injected alprostadil, and Muse, another alprostadil, which is administered intraurethrally. At least two topical gel versions are in the works and may be on the market within a year or so.

Another prescription medication, Regitine (it's generic name is phentolamine) is also an impotence 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 impotence. 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.

This article has been revised by Vhihealthe for its audience and may contain, among other things, information or medical practices that are unique to Ireland. Neither Consumer Health Interactive nor the original author make any warranty as to the accuracy of the article as revised, and assume no responsibility for modified content.

First published November 21, 2000
Copyright © 2000 Consumer Health Interactive

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