Sunday, August 12, 2007

Side Effects of Viagra®

Very few drugs work perfectly, and Viagra® is no exception. Just about every drug has side effects that arise because the drug is flowing throughout the body and may affect parts of the body unintentionally. For example, aspirin is a drug that relieves pain, but this same drug can also erode the stomach lining and thin the blood. Those are side effects of aspirin.

Viagra® has several side effects of which patients need to be aware.

The first problem comes because Viagra® happens to have a spillover effect. It blocks PDE5, but it also has an effect on PDE6. It turns out that PDE6 is used in the cone cells in the retina, so Viagra® can have an effect on color vision. Many people who take Viagra® notice a change in the way they perceive green and blue colors, or they see the world with a bluish tinge for several hours. For this reason, pilots cannot take Viagra® within 12 hours of a flight.

The second problem comes for people who are taking drugs like nitroglycerin for angina. Nitroglycerin works by increasing nitric oxide, and it helps with angina by opening up the arteries that supply the heart with oxygen. If you take nitroglycerin and Viagra® together, the increased nitric oxide plus the blocking of PDE5 can lead to problems.

Other problems with Viagra® can include little things like headaches (the drug, as a side effect in some men, opens up arteries in the brain's lining and causes excess pressure) and big things like heart attacks. The possibility of heart attacks is one reason why Viagra® is a prescription drug rather than an over-the-counter drug like aspirin. A doctor needs to understand your medical history and make sure that Viagra® won't cause a heart attack. Occasional patients who take Viagra® get painful, long-lasting erections and have to see a doctor to solve the problem.

Finally, there is some concern that some men, especially younger men who take Viagra® recreationally and who don't really need it for physical reasons, may end up with a dependency on the drug. That is, they may become unable to maintain an erection without taking Viagra®.

For more information about side effects, see RxList: Viagra® Side Effects.

What about Cialis® and Levitra®?
Viagra® is a hugely successful drug, and other drug companies wanted a piece of the action. They developed different chemicals to block the PDE5 enzyme and created two new drugs: Cialis® (tadalafil) and Levitra® (vardenafil).

Because Cialis® and Levitra® block the PDE5 enzyme, they work exactly the same way as Viagra®. They help men who have trouble maintaining an erection because of blood flow problems, and they only work when the man is sexually aroused.

Because they block PDE5 with different chemicals, however, there are some important differences between the three drugs. For example:

* Only Viagra® causes color-vision problems.
* Cialis® causes muscle aches in about 5 percent of patients.
* Viagra® and Levitra® last about four hours in the bloodstream. Cialis® stays in the bloodstream much longer (it has a 17.5-hour half life) and can therefore be effective for more than a day.