In the short space of just three years, Viagra has revolutionized the treatment of erectile dysfunction (ED). Millions of men have had their sexual potency restored by the little blue diamond, and researchers are testing to see if it might also benefit women with certain types of sexual dysfunction

Despite its popularity and broad availability, though, there are a number of popular misconceptions about Viagra. To correct them, we offer this closer look at what it does, what it doesn't do, its potential side effects, and the conditions under which it should never be used.

How It Works

How does Viagra promote an erection? The centers of action are two columns of erectile tissue in the penis called the corpora cavernosa (we'll abbreviate them here as 'CC'). During sexual arousal, the CC are designed to stretch and fill with blood, causing an erection. "Inflation" of the CC with blood is what causes the penis to become stiff and rigid.

That's the basic picture, but to understand it fully, one must learn a bit about two important biochemicals at play. Sexual arousal causes the body to produce increased amounts of a compound called cyclic guanosine monophosphate (cGMP) in the corpora cavernosa. The role of cGMP is to relax the smooth-muscle walls of the CC, allowing them to stretch and overfill with blood.

Being able to obtain and maintain an erection is a good thing (most men would agree), but eventually, you want it to subside. That's where another biochemical, an enzyme called phosphodiesterase type 5 (PDE5), comes into play. PDE5 is always present in the CC; it's job is to degrade cGMP, thus ending the smooth-muscle relaxation that made erection possible in the first place.

So, what about the little blue pill? What Viagra does is inhibit the action of PDE5. This makes it easier to achieve high levels of cGMP, smooth muscle relaxation, and inflow of blood to the CC.

Of Drugs and Desire

While Viagra is very effective in meeting its very specific objective, the assumption that it's an all-around sex-enhancer would be wrong. "Viagra is not an aphrodisiac for men with normal function, and it does not increase the number of orgasms a man is going to have," says Andrew McCullough, MD, assistant professor of urology at New York University and director of NYU's Male Sexual Health and Fertility Clinic.

Additionally, Viagra has no effect in the absence of sexual stimulation, at least not at the recommended doses. It will not restore libido. It will not cure premature ejaculation, nor will it overcome an inability to ejaculate. All Viagra does is help you obtain and maintain an erection-if your body is having trouble doing the job on its own.

As for side effects, Viagra has proved, so far, to be remarkably safe and well tolerated ("well tolerated" meaning the side effects are not so unpleasant as to make you stop using it). According to the manufacturer (Pfizer), the most common side effects reported in clinical studies of Viagra were headache in 16% of patients; flushing in 10%; stomach upset in 7%; nasal congestion in 4%; urinary tract infection, abnormal vision (slight, temporary color blindness or sensitivity to light), and diarrhea in 3%, each; and dizziness and rash in 2%, each. These side effects are generally mild, and, in any case, the "adverse events" reported in clinical studies may be unrelated to the drug being studied.

When Viagra Might Be Harmful

You may have heard about a number of deaths in men who were taking Viagra, back when it first came on the market. Some of those deaths were associated with Viagra, but not directly; they were caused by the interaction of Viagra with a class of heart medications called organic nitrates (nitroglycerin is an example). Organic nitrates dilate (relax and expand) blood vessels. The inhibition of PDE5 by Viagra increases this relaxation to the point that a person's blood pressure can plummet suddenly to deadly levels. Viagra should never be used in combination with organic nitrates, and this caution includes the concurrent use of nitrate inhalants ("poppers").

A variety of press reports over the past two years have described the use of Viagra as a sex-enhancer or recreational drug in some settings-and even as part of a drug "cocktail" along with popular street drugs such as cocaine, marijuana, and "poppers." McCullough says that, overall, the profile of those getting Viagra prescriptions has closely mirrored the prevalence of ED-essentially men over the age of 40-"with barely a blip" in the party-going younger age set. But he notes the potential for abuse, which is especially dangerous in the case of inhalants ("poppers"). In combination with amyl nitrate, McCullough says, "Viagra is potentially lethal."

Viagra also interacts with some antibiotics, antivirals, and antifungals, though not in a deadly fashion. The nature of these interactions is that they can cause increased blood levels of Viagra by inhibiting its natural breakdown in the body. Viagra can be used in combination with these drugs, but safe use requires a reduction in the dose of Viagra. "The only medication that is absolutely contraindicated for Viagra or any of the new PDE-5 inhibitors is the nitrate family," says McCullough. "The other drug interactions simply require a minor dose adjustment."

Experts are quick to stress that Viagra is not for everyone. It should never be prescribed until a thorough medical examination and evaluation of the patient has been completed. If you haven't been through such an examination and evaluation, you shouldn't be taking Viagra.

The Root of the Problem