Sildenafil comes as a tablet to take by mouth. It should be taken as needed about 1 hour before sexual activity. However, sildenafil can be taken anytime from 4 hours to 30 minutes before sexual activity. Sildenafil should not be taken more than once a day. Follow the directions on your prescription label carefully, and ask your doctor or pharmacist to explain any part you do not understand. Take sildenafil exactly as directed. Do not take more or less of it or take it more often than prescribed by your doctor.

Although side effects from sildenafil are not common, they can occur. Tell your doctor if any of these symptoms are severe or do not go away:

headache
upset stomach
diarrhea
dizziness or lightheadedness
flushing (feeling of warmth)
nasal congestion (stuffiness)
changes in vision
breast enlargement
If you experience any of the following symptoms, call your doctor immediately:

rash
painful erection
prolonged erection (longer than 4 hours)
fainting
chest pain
itching or burning during urination

In case of overdose, call your local poison control center at 1-800-222-1222. If the victim has collapsed or is not breathing, call local emergency services at 911.

Keep all appointments with your doctor. Sildenafil is not effective in preventing the spread of AIDS or other sexually transmitted diseases.

Do not let anyone else take your medication. Ask your pharmacist any questions you have about refilling your prescription.

Sildenafil is used to treat impotence in men. Sildenafil increases the body's ability to achieve and maintain an erection during sexual stimulation.

This medication is sometimes prescribed for other uses; ask your doctor or pharmacist for more information.

Keep this medication in the container it came in, tightly closed, and out of reach of children. Store it at room temperature and away from excess heat and moisture (not in the bathroom). Throw away any medication that is outdated or no longer needed. Talk to your pharmacist about the proper disposal of your medication.

Before taking sildenafil,

tell your doctor and pharmacist if you are allergic to sildenafil or any other drugs.
tell your doctor and pharmacist what prescription and nonprescription medications you are taking, especially amlodipine (Norvasc) or other medications for high blood pressure, cimetidine (Tagamet, Tagamet HB), erythromycin, HIV protease inhibitors such as ritonavir (Norvir) and saquinavir (Invirase), isosorbide (Imdur, Ismo, Isordil, and others), itraconazole (Sporanox), ketoconazole (Nizoral), nitroglycerin (Nitro-Bid, Nitrostat, and others), other medications to treat impotence, phenobarbital, rifampin (Rifadin, Rimactane),and vitamins.
tell your doctor if you have or have ever had a bleeding disorder; heart, kidney, or liver disease; a heart attack; irregular heartbeats; angina; a stroke; high or low blood pressure; sickle cell anemia; multiple myeloma; leukemia; conditions affecting the shape of the penis (e.g., angulation, cavernosal fibrosa, or Peyronie's disease); or a condition known as retinitis pigmentosa.
if you are having surgery, including dental surgery, tell your doctor or dentist that you take sildenafil.
tell your doctor if you use amyl nitrate, amyl nitrite, or butyl nitrate.