About Viagra

Viagra is a treatment for men with erectile dysfunction (sometimes referred to as ED or impotence). This is when a man cannot get, or keep, a hard and erect penis suitable for sexual activity.

Viagra belongs to a group of medicines called 'phosphodiesterase type 5 (PDE 5) inhibitors'.

Viagra is only for use by men with erectile dysfunction, and it only works when a man is sexually stimulated.

Viagra contains an active ingredient called sildenafil. Sildenafil helps to relax the blood vessels in the penis, allowing more blood to flow into the penis when you are sexually aroused, which causes an erection.

Viagra should be taken with a glass of water, one hour before you plan to have sex. The correct dose of Viagra can only be decided by a doctor, and no more than one dose should be taken per day.

If more than one dose of Viagra is taken in a day, contact the doctor immediately for advice. Exceeding the recommended dose of Viagra may cause an increase in side effects and their severity.

Viagra, like all medicines, can cause side effects. But not everybody experiences them.

During the testing phases, the most commonly reported side effects in patients treated with Viagra were headache, facial flushing, indigestion, mild and temporary visual changes (colour perception changes, light perception changes, blurred vision or reduced sharpness of vision), stuffy nose and dizziness. These side effects were usually mild-to-moderate and did not last long.

If you are worried about any side effects, make sure you talk to your doctor.

Viagra usually takes around 30 minutes to an hour to work. However, taking Viagra with a heavy meal can mean it takes a bit longer.

Viagra can produce an erection in response to sexual stimulation for approximately 4 to 5 hours after taking it.

Viagra does not cause an automatic erection that cannot be controlled and only works in response to sexual stimulation.

Viagra does not cause an instant or uncontrollable erection – sexual stimulation is needed for an erection to occur. After sexual intercourse or when no longer sexually excited, the erection will go away as normal.

If an erection ever lasts for more than 4 hours, contact a doctor immediately.

Viagra can be taken either with or without food. But if Viagra is taken with a heavy meal, it can take longer to work.

Drinking alcohol can temporarily impair the ability to get an erection. To get the maximum effect from Viagra, drinking excessive amounts of alcohol is not advised.

There are significant risks associated with combining recreational drugs with Viagra. In particular, nitrates – found in amyl nitrate/'poppers' – can cause a serious drop in blood pressure if taken with Viagra.

You can take Viagra at the same time as many common medications. However, Viagra should not be taken with other medicines without a doctor's approval - that includes medicines obtained without prescription.

Viagra should never be taken with nitrates - often used to treat chest pain - as the combination of these medicines may cause a potentially dangerous decrease in blood pressure.

If Viagra is taken alongside alpha-blocker therapy – used to treat high blood pressure or prostate enlargement – then sitting or standing up quickly may cause dizziness or light-headedness.

In the event of a medical emergency, the healthcare professional treating the condition should be told that Viagra has been taken and when it was taken.

While men may continue to need Viagra as long as they have erection problems, this does not mean they are dependent on, or addicted to Viagra. There is no evidence to suggest Viagra is addictive.

Viagra is not an aphrodisiac and will not increase sexual desire.

There is no evidence to suggest Viagra affects fertility.

Viagra tablets are blue, film-coated, and are a rounded-diamond shape. They are marked "PFIZER" on one side and "VGR 25, "VGR 50" or "VGR 100" on the other. The tablets are provided in blister packs containing 2, 4, 8 or 12 tablets.

The only way to be sure that Viagra is genuine is to get it by prescription through legitimate sources. You can find out more about that in the don't take risks section.

To view the latest patient information leaflet and summary of product characteristics visit:

The electronic Medicines Compendium (eMC)