Viagra (sildenafil) is usually safe for most men, but some people should stay away from it or use it carefully because it could be bad for their health. Persons in the following groups shouldn't take Viagra without first talking to a doctor or nurse:
Those who take nitrate medicines for heart problems, like nitroglycerin, should not take Viagra together with these medicines because it can cause a dangerous drop in blood pressure.
Alpha-Blockers: People who are taking alpha-blockers for conditions like a big prostate should be careful when they take Viagra together because it could lower their blood pressure.
Serious Health Conditions: People who have had a recent stroke or heart attack, have serious heart or liver problems, or certain eye conditions should talk to a doctor before taking Viagra.
If you are allergic to sildenafil or any of the other ingredients in Viagra, you should not take it.
Before taking Viagra or any other prescription drug, you should always talk to a doctor or nurse to get specific advice.