Viagra (sildenafil) is a popularly prescribed anti- impotence drug that can be used for the treatment of erectile dysfunction in males of any age. This condition needs to be treated, but cannot be cured in most cases. It means that you will need to take Viagra each time you want to have sex, but not more often than every 24 hours. Besides, there are a number of risk factors and contraindications associated with using Viagra. If you are taking nitrate-based drugs, for example, you will be unable to use Viagra because of high risk of developing sudden drop in blood pressure that can lead to consequences that are more serious. Tell your doctor about any other drugs you are using at the moment, especially antifungal medications, rifampin, antibiotics, isoniazid, diclofenac, enoxacin, heart or blood pressure medications, conivaptan, cimetidine, HIV/AIDS medicines, antidepressants, imatinib, bosentan, or any other prescription or over-the-counter products you are taking at the moment. Viagra may cause a few mild side effects, especially when you first start using it, but they are not too serous and are not expected to last for too long. Tell your doctor if your mild side effects, such as memory problems, stuffy nose, upset stomach, back pain, warmth or redness in your face or chest, or headache do not go away.