Patient information:
Viagra inhibits an enzyme called phosphodiesterase 5 (PDE5) which is found primarily in the penis. The enzyme, PDE5 breaks down cyclic GMP. Cyclic GMP is produced during sexual stimulation, leading to penis erection. The longer the cyclic GMP persists, increased blood flows to the penis, thereby generating an erection.Following sexual stimulation Viagra works by helping the blood vessels in your penis to relax, allowing the flow of blood into your penis. The result of this is improved erectile function.

It is important to note that Viagra does not work if there is no sexual stimulation.

Direction :
Always take Viagra exactly as your doctor has instructed you. Viagra is taken about one hour before sexual activity and it will only work when you are sexually stimulated. Viagra tablets are for oral use. Swallow the tablet whole with some water. Avoid taking High-fat food before taking Viagra as it may cause the medicine to take more time to start working. The ability to have sexual activity improves up to 4 hours after taking Viagra. Do not take Viagra more than once a day. Viagra doses range from 25 milligrams, 50 milligrams and 100 milligrams. Your doctor will adjust the dosage if the drug is not working properly for you.

Side Effects:
The most common side effects include headache, flushing, upset stomach, abnormal vision, diarrhea, dizziness, and rash.

Precautions
It is important that the doctor has your complete medical history. Consult with your doctor if you have a cardiovascular condition, such as high blood pressure, kidney impairment, liver impairment, sickle cell anemia, multiple myeloma, leukemia, and anatomical deformations of the penis, bleeding disorders, or retinitis pigmentosa.

Drug interactions
Tell your doctor of all nonprescription and prescription medication you may use, especially any nitrate medications (e.g., nitroglycerin, isosorbide dinitrate), nitroprusside (any "nitric oxide donor" medicines), quinidine, quinine, verapamil, cimetidine, erythromycin, clarithromycin, azole antifungals (e.g., itraconazole, ketoconazole, fluconazole), mibefradil, niacin, omeprazole, rifamycins (e.g., rifampin) medication for HIV infection or high blood pressure medicines.