Before taking Viagra, let your doctor know If you are using nitrates for chest pain or any heart problems, Viagra can interact with the nitrate drugs and guide you to complex health conditions like fainting, stroke, low blood pressure or cardiac arrest. Recreational drugs too contain nitrates.

Sometimes you experience a sudden loss of vision, caused by the decreased flow of blood to the optic nerve, generally known as NAION, when you take Viagra. It generally occurs among people who suffer from medical conditions like cardiac problems, high blood pressure, diabetes, high cholesterol, smokers above 50 years or people with pre-existing eye problems.

Before taking Viagra, you must let your doctor know if you have any of the following medical problems:

• Recent history of stroke or heart attack
• Any type of heart related problems
• Kidney problems
• Liver diseases
• Both high as well as low blood pressure
• Diseases of the coronary artery
• Blood cell disorders like leukemia, sickle cell anemia
• Ulcer of the stomach
• Hemophilia
• Color vision
• Peyronie's disease, or penis deformation
• Inability to have sexual intercourse for health reasons