Viagra (sildenafil) is an anti-impotence agent available by prescription and efficient in helping the patients taking it to achieve a hard erection and have sex. Make sure you report to your health care provider any of the following medical conditions: heart attack, history of a stroke, kidney disease, bleeding disorder, stomach ulcer, coronary artery disease, blood cell disorder, and abnormal blood pressure. These are very important to report as your dose can depend on them as well. Your age, general health condition and severity of your impotence are other factors that can affect the dose you are prescribed. You are not supposed to share Viagra with anyone because every dose is individual and based on different needs. Tell your doctor if you are taking or plan to take any of the following mediations as they can cause interference with Viagra: conivaptan, bosentan, rifampin, antifungals, diclofenac, isoniazid, HIV/AIDS medicines, antidepressants, enoxacin, imatinib, heart or blood pressure medications, antibiotics, and cimetidine. Viagra side effects are not numerous and can include facial flushing, nasal congestion, color vision problems, diarrhea, nausea, headaches, and stomach pain.