What is Viagra?
 Viagra (sildenafil) relaxes muscles and increases blood flow to particular areas of the body.
Sildenafil  under the name Viagra is used to treat erectile  dysfunction  (impotence) in men. Another brand of sildenafil is Revatio,  which is  used to treat pulmonary arterial hypertension and improve  exercise  capacity in men and women. Do not take Viagra while also taking   Revatio, unless your doctor tells you to
Important about Viagra
   Do  not take Viagra if you are  also using a nitrate drug for chest  pain or  heart problems. This  includes nitroglycerin (Nitrostat,  Nitrolingual,  Nitro-Dur, Nitro-Bid,  and others), isosorbide dinitrate  (Dilatrate-SR,  Isordil,  Sorbitrate), and isosorbide mononitrate (Imdur,  ISMO,  Monoket).  Nitrates are also found in some recreational drugs such  as  amyl  nitrate or nitrite ("poppers"). Taking Viagra with a nitrate   medicine  can cause a sudden and serious decrease in blood pressure.   During  sexual activity, if you become dizzy or nauseated, or have pain,    numbness, or tingling in your chest, arms, neck, or jaw, stop and call    your doctor right away. You could be having a serious side effect of    Viagra.
Do not take  Viagra more than once a day. Allow 24 hours  to pass  between doses.  Contact your doctor or seek emergency medical  attention  if your  erection is painful or lasts longer than 4 hours. A  prolonged  erection  (priapism) can damage the penis.
Viagra can  decrease blood flow to the optic nerve of the eye, causing   sudden  vision loss. This has occurred in a small number of people   taking  Viagra, most of whom also had heart disease, diabetes, high  blood   pressure, high cholesterol, or certain pre-existing eye  problems, and   in those who smoke or are over 50 years old. It is not  clear whether   Viagra is the actual cause of vision loss.
Stop using Viagra and get emergency medical help if you have sudden vision loss.
Before taking Viagra
Do not take Viagra if you are also  using a nitrate drug for chest  pain or heart problems. This includes  nitroglycerin (Nitrostat,  Nitrolingual, Nitro-Dur, Nitro-Bid, and  others), isosorbide dinitrate  (Dilatrate-SR, Isordil, Sorbitrate), and  isosorbide mononitrate (Imdur,  ISMO, Monoket). Nitrates are also found  in some recreational drugs such  as amyl nitrate or nitrite ("poppers").  Taking Viagra with a nitrate  medicine can cause a sudden and serious  decrease in blood pressure.
To make sure you can safely take Viagra, tell your doctor if you have any of these other conditions:
-  heart disease or heart rhythm problems;
 
-  a recent history (in the past 6 months) of a heart attack, stroke, or congestive heart failure;
 
-  high or low blood pressure;
 
-  coronary artery disease;
 
-  liver or kidney diseas;
 
-  a blood cell disorder such as sickle cell anemia, multiple myeloma, or leukemia;
 
-  a bleeding disorder such as hemophilia;
 
-  a stomach ulcer;
 
-  retinitis pigmentosa (an inherited condition of the eye);
 
-  a physical deformity of the penis (such as Peyronie's disease); or
 
- if you have been told you should not have sexual intercourse for health reasons
       Viagra can decrease blood flow to the optic nerve of the eye, causing   sudden vision loss. This has occurred in a small number of people   taking Viagra, most of whom also had heart disease, diabetes, high blood   pressure, high cholesterol, or certain pre-existing eye problems, and   in those who smoke or are over 50 years old. It is not clear whether   Viagra is the actual cause of vision loss. Stop using Viagra and get   emergency medical help if you have sudden vision loss.
FDA pregnancy category B: This medication is not expected to be harmful to an unborn baby. Do not use Viagra without telling your doctor if you are pregnant or plan to become pregnant during treatment. It is not known if sildenafil passes into breast milk or if it could harm a nursing baby. Do not use this medication without telling your doctor if you are breast-feeding a baby
FDA pregnancy category B: This medication is not expected to be harmful to an unborn baby. Do not use Viagra without telling your doctor if you are pregnant or plan to become pregnant during treatment. It is not known if sildenafil passes into breast milk or if it could harm a nursing baby. Do not use this medication without telling your doctor if you are breast-feeding a baby
Viagra side effects 
      
Get emergency medical help if you have any of these signs of an allergic reaction: hives; difficulty breathing; swelling of your face, lips, tongue, or throat. During sexual activity, if you become dizzy or nauseated, or have pain, numbness, or tingling in your chest, arms, neck, or jaw, stop and call your doctor right away. You could be having a serious side effect of Viagra.
Stop using Viagra and call your doctor at once if you have a serious side effect such as:
Get emergency medical help if you have any of these signs of an allergic reaction: hives; difficulty breathing; swelling of your face, lips, tongue, or throat. During sexual activity, if you become dizzy or nauseated, or have pain, numbness, or tingling in your chest, arms, neck, or jaw, stop and call your doctor right away. You could be having a serious side effect of Viagra.
Stop using Viagra and call your doctor at once if you have a serious side effect such as:
-  sudden vision loss;
 
-  ringing in your ears, or sudden hearing loss;
 
-  chest pain or heavy feeling, pain spreading to the arm or shoulder, nausea, sweating, general ill feeling;
 
-  irregular heartbeat;
 
-  swelling in your hands, ankles, or feet;
 
-  shortness of breath;
 
-  vision changes;
 
-  feeling light-headed, fainting; or
 
- penis erection that is painful or lasts 4 hours or longer.
Less serious Viagra side effects may include:
-  warmth or redness in your face, neck, or chest;
 
-  stuffy nose;
 
-  headache;
 
-  memory problems;
 
-  upset stomach; or
 
-  back pain.
 
  This is not a complete list of side effects and others may occur.  Call  your doctor for medical advice about side effects. You may report  side  effects to FDA at 1-800-FDA-1088.
See also: Viagra side effects (in more detail)
Where can I get more information?
See also: Viagra side effects (in more detail)
Where can I get more information?
- Your pharmacist can provide more information about Viagra.
What does my medication look like? 
Sildenafil is available with a prescription under the brand names Viagra and Revatio. Other brand or generic formulations may also be available. Ask your pharmacist any questions you have about this medication, especially if it is new to you.
Sildenafil is available with a prescription under the brand names Viagra and Revatio. Other brand or generic formulations may also be available. Ask your pharmacist any questions you have about this medication, especially if it is new to you.
-  Revatio 20 mg - white, film-coated round tablets
 
-  Viagra 25 mg - blue, film-coated tablets with a rounded-diamond shape
 
-  Viagra 50 mg - blue, film-coated tablets with a rounded-diamond shape
 
- Viagra 100 mg - blue, film-coated tablets with a rounded-diamond shape