As you’ve probably heard, Viagra (Sildenafil) is used to treat 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
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.
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.
