emt_aj replied: "Sildenafil is used to treat male sexual function problems (impotence or erectile dysfunction) by blocking a certain enzyme (phosphodiesterase-PDE5) in the body. In combination with sexual stimulation, sildenafil works by helping the blood flow into the penis to achieve and maintain an erection. This drug is not indicated for use in women. Use of this drug does not protect against sexually transmitted diseases (e.g., HIV, hepatitis B, gonorrhea, syphilis). Practice "safe sex" such as using latex condoms. Consult your doctor or pharmacist for more details USES This drug is taken by mouth as needed, at least 30 minutes, but no more than 4 hours, before sexual activity (1 hour before is the most effective). Do not take more often than once daily, and take as directed. A high fat meal may delay the time of onset of this drug. Avoid eating grapefruit or drinking grapefruit juice while you are being treated with this medication unless your doctor instructs you otherwise. SIDE EFFECTS The dosage is based on your medical condition, response to therapy, and other medications you may be taking (see also Drug Interactions section). Consult your doctor or pharmacist for more details. Headache, flushing, stomach upset, heartburn, nasal stuffiness, diarrhea, dizziness, or lightheadedness may occur. Vision changes such as increased sensitivity to light, blurred vision, or impaired blue/green color discrimination may also occur. If any of these effects persist or worsen, notify your doctor or pharmacist promptly. Remember that your doctor has prescribed this medication because the benefit to you is greater than the risk of side effects. Many people using this medication do not have serious side effects. Rarely, a sudden loss of eyesight in one or both eyes (NAION) may occur. This may or may not be due to sildenafil. If this serious problem occurs, seek immediate medical attention. You have a slightly greater chance of developing this serious eye problem if you have heart disease, diabetes, high cholesterol, certain eye problems ("crowded disk"), high blood pressure, are over 50 years of age, or if you smoke. Sexual activity may put extra strain on your heart, especially if you have heart problems. If you have heart problems and experience any of these serious side effects while having sex, stop and tell your doctor immediately of: severe dizziness, fainting, chest pain, nausea. For males, in the very unlikely event you have a painful or prolonged erection lasting 4 or more hours, stop using this drug and seek immediate medical attention, or permanent problems could occur. A serious allergic reaction to this drug is unlikely, but seek immediate medical attention if it occurs. Symptoms of a serious allergic reaction include: rash, itching, unusual swelling, severe dizziness, trouble breathing. If you notice other effects not listed above, contact your doctor or pharmacist. PRECAUTIONS Before taking sildenafil, tell your doctor or pharmacist if you are allergic to it; or if you have any other allergies. Before using this medication, tell your doctor or pharmacist your medical history, especially of: penis conditions (e.g., angulation, fibrosis/scarring, Peyronie's disease), history of painful/prolonged erection (priapism), sickle cell anemia, blood system cancers (e.g., leukemia or myeloma), eye problems (e.g., retina diseases like retinitis pigmentosa), kidney disease, liver disease, bleeding disorders, active stomach ulcers, heart problems (e.g., recent heart attack or serious arrhythmia within past 6 months, heart failure, coronary artery disease with unstable angina, aortic stenosis, idiopathic hypertrophic subaortic stenosis), recent stroke within past 6 months, very high or low blood pressure. This drug may make you dizzy or cause vision changes; use caution engaging in activities requiring alertness such as driving or using machinery. Limit alcoholic beverages. To minimize dizziness and lightheadedness, get up slowly when rising from a seated or lying position. Caution is advised when using this drug in the elderly because they may be more sensitive to the side effects of the drug. This drug is not indicated for use in women or children. This drug should not be used with the following medications because very serious (possibly fatal) interactions may occur: nitrates (e.g., nitroglycerin, isosorbide), nitroprusside (or any "nitric oxide donor" drugs), recreational drugs called "poppers" containing amyl or butyl nitrite. DRUG INTERACTONS If you are currently using any of these medications, tell your doctor or pharmacist before starting sildenafil. Before using this medication, tell your doctor or pharmacist of all prescription and nonprescription products you may use, especially of: alpha-blocker medication (e.g., doxazosin, prazosin, terazosin), other medications for impotence, azole antifungals (e.g., itraconazole, ketoconazole), bosentan, cimetidine, erythromycin, rifamycins (e.g., rifampin), high blood pressure medicines, delavirdine. If you are taking an HIV protease inhibitor (e.g., ritonavir, saquinavir), do not take more than a 25mg dose of sildenafil in a 48 hour period. If you are taking more than a 25mg dose of sildenafil and are also taking an alpha-blocker medication (e.g., doxazosin, prazosin, terazosin) for various conditions (e.g., enlarged prostate), separate the time between taking these medications by more than 4 hours. Do not start or stop any medicine without doctor or pharmacist approval. I hope all this information helps."