Viagra (sildenafil citrate) is a prescription drug intended for patients that experience temporary or permanent problems with getting an erection that would be hard enough to have sex. Viagra is prescribed in three different dosages - 25, 50 and 00 mg of the active ingredient. The dose may be lower if you are older than 60 or have such medical problems as kidney disease, heart attack, blood cell disorder, history of a stroke, coronary artery disease, stomach ulcer, bleeding disorder, or abnormal blood pressure, or higher if your doctor deems it necessary. Before you start using Viagra, make sure you are not taking any drugs that may affect your wellbeing in any way. Your doctor will need to know if you are using cimetidine, HIV/AIDS medicines, antidepressants, imatinib, antifungals, isoniazid, rifampin, diclofenac, antibiotics, enoxacin, heart or blood pressure medications, conivaptan, or bosentan, as well as any other prescription or over-the-counter products. Viagra has been reported to interfere with alcohol (you get worsened side effects) and grapefruit juice (can slow down the absorption of this drug). Avoid taking Viagra more often than every 24 hours.