Drug Uses
Viagra is used for treating erectile dysfunction (e.g. male impotence). It works by helping the blood flow into the penis to achieve and maintain an erection during sexual stimulation.

How to use
Viagra is to be taken 30 minutes to 1 hour before sexual activity. You may take it up to 4 hours before sexual activity. Viagra is not supposed to be taken more often than once per day.

Drug Class and Mechanism
Viagra is a phosphodiesterase type 5 inhibitor and it works by helping the blood flow into the penis to achieve and maintain an erection during sexual stimulation.

Missed Dose
Viagra is to be used as necessary, so you are not supposed to take it according to a schedule.

Storage
Viagra is to be kept in its original container. It is to be stored at room temperature between 59 and 86 degrees F (15-30 degrees C) away from moisture, heat and light and out of the reach of children.

Warnings/Precautions

Do not take Viagra, if you are also using a nitrate drug for chest pain or heart problems, including nitroglycerin (Nitrostat, Nitrolingual, Nitro-Dur, Nitro-Bid, Minitran, Deponit, Transderm-Nitro), isosorbide dinitrate (Dilatrate-SR, Isordil, Sorbitrate), and isosorbide mononitrate (Imdur, ISMO, Monoket), or recreational drugs such as amyl nitrate or nitrite ("poppers").

Before taking Viagra, tell your doctor about all other medications you use for erectile dysfunction, or if you are using any of the following medications:

* bosentan (Tracleer);
* a blood thinner such as warfarin (Coumadin);
* cimetidine (Tagamet, Tagamet HB);
* an antibiotic such as erythromycin (E-Mycin, Eryc, Ery-Tab) or clarithromycin (Biaxin);
* doxazosin (Cardura), prazosin (Minipress), Terazosin (Hytrin);
* HIV medicines such as amprenavir (Agenerase), tipranavir (Aptivus), darunavir (Prezista), efavirenz (Sustiva), nevirapine (Viramune), indinavir (Crixivan), saquinavir (Invirase, Fortovase), lopinavir/ritonavir (Kaletra), fosamprenavir (Lexiva), ritonavir (Norvir), atazanavir (Reyataz), or nelfinavir (Viracept);
* an antifungal medication such as itraconazole (Sporanox) or ketoconazole (Nizoral);
* carbamazepine (Tegretol), phenobarbital (Luminal), or phenytoin (Dilantin); or
* rifampin (Rifadin, Rimactane) or rifabutin (Mycobutin).

Tell your doctor about all the prescriptions and over-the-counter medications you use. This includes vitamins, minerals, herbal products, and drugs prescribed by other doctors. Do not start using a new medication without telling your doctor.

If you have heart problems severe enough to make sexual activity a dangerous, you should avoid using Viagra. Use it cautiously, if you've had a heart attack, stroke, or life-threatening heart irregularities within the past 6 months. Be equally cautious, if you have severe high or low blood pressure, heart failure or unstable angina.

In case of cardiac symptoms developing (for example, dizziness, nausea, and chest pain) during sexual activity, do not continue. Tell your doctor about the problem as soon as possible.

If you have a condition that might result in long-lasting erections, such as sickle cell anemia, multiple myeloma (a disease of the bone marrow), or leukemia, use Viagra with caution. Also use cautiously if you have a genital problem or deformity such as Peyronie's disease. If an erection lasts more than 4 hours, seek treatment immediately. Permanent damage and impotence could result.

If you have a bleeding disorder, a stomach ulcer, or the inherited eye condition known as retinitis pigmentosa, use Viagra with caution. Its safety under these circumstances has not been studied yet.

Possible Side Effects

If you experience any of the following serious side effects, stop taking Viagra and seek emergency medical attention or notify your doctor immediately:

* 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 side effects may include:

* warmth or redness in your face, neck, or chest;
* stuffy nose;
* headache;
* upset stomach; or
* back pain.

This is not a complete list of side effects and others may occur. Tell your doctor about any unusual or bothersome side effect. More Information

If you are older than 65 years, you can suffer Viagra side effects. However, your physician may prescribe you a lower dose of this medication.