Sildenafil for erectile dysfunction

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  • Sildenafil is for erectile dysfunction - do not take it if you do not have erectile dysfunction.
  • Take a tablet one hour before you plan to have sex.
  • When you collect your prescriptions, check that you have been given the same brand of tablets as before. If the appearance is not the same as usual, speak with your doctor or pharmacist.
Type of medicinePhosphodiesterase type-5 inhibitor
Used forErectile dysfunction in adult men
Also calledViagra®
Available asTablets

Erectile dysfunction (sometimes called impotence) means that you cannot get or maintain a proper erection. There are several causes, the most common being due to a narrowing of the arteries that take blood to the penis.

Sildenafil works by preventing the action of a chemical in the body called phosphodiesterase type 5. This helps to relax (widen) blood vessels and improves the flow of blood. In erectile dysfunction, sildenafil improves the blood flow to the penis following sexual stimulation, and this helps to maintain an erection.

Sildenafil is available on prescription. Do not take it if you do not have erectile dysfunction.

Another brand of sildenafil tablets called Revatio® is used in a completely different condition called pulmonary arterial hypertension. This is a specialist treatment and no information about this brand of sildenafil is included in this medicine leaflet.

Some medicines are not suitable for people with certain conditions, and sometimes a medicine may only be used if extra care is taken. For these reasons, before you start taking sildenafil it is important that your doctor or pharmacist knows:

  • If you have any disease, injury or deformity of your penis.
  • If you have heart or blood vessel disease.
  • If you have a condition which causes bleeding, such as a stomach ulcer.
  • If you have had an eye condition causing loss of vision.
  • If you have low blood pressure or angina.
  • If you have liver or kidney problems.
  • If you have had a stroke or a heart attack.
  • If you have sickle-cell disease.
  • If you have ever had bone marrow cancer or leukaemia.
  • If you are taking or using any other medicines. This includes any medicines you are taking which are available to buy without a prescription, such as herbal and complementary medicines. It is important that your doctor knows if you are using a medicine prescribed for angina pain, or if you are using a 'nitrite' drug (such as in the recreational drug known as 'poppers').
  • If you have ever had an allergic reaction to this or to any other medicine.
  • Before you take sildenafil, read the manufacturer's printed information leaflet from inside your pack. The leaflet will give you more information about the tablets, and also a full list of the side-effects you may experience.
  • Take sildenafil exactly as your doctor has told you. You should take one tablet one hour before you plan to have sex. You can take the tablet before or after food but, if you have just eaten a large meal, it will take longer for it to work.
  • Do not take sildenafil more frequently than once a day.
  • You and your partner will still need to engage in foreplay, just as you would if you were not taking a medicine for erectile dysfunction. Sildenafil will not cause an erection unless you are sexually aroused.
  • Do not drink large amounts of alcohol with sildenafil. Drinking too much alcohol can reduce your ability to get an erection and this may prevent you from getting the maximum benefit from these tablets.
  • Do not drink grapefruit juice with sildenafil. This is because a chemical in grapefruit juice increases the amount of sildenafil in your bloodstream. This makes side-effects more likely.
  • If you feel the tablets are too strong for you, discuss this with your doctor as your dose may need to be reduced.
  • If you do not get an erection after taking sildenafil, or if it does not last long enough for you to have sex, discuss this with your doctor. Do not take more tablets than you have been told to.
  • You should not take sildenafil if you are using any other products or taking any other medicines to treat erectile dysfunction.

Along with their useful effects, most medicines can cause unwanted side-effects although not everyone experiences them. These usually improve as your body adjusts to the new medicine, but speak with your doctor or pharmacist if any of the following side-effects continue or become troublesome.

Common sildenafil side-effectsWhat can I do if I experience this?
HeadacheAsk your pharmacist to recommend a suitable painkiller
Flushed face, indigestion, blocked nose, blurred vision, sensitivity to lightThese should soon pass
Feeling dizzyIf this happens, do not drive or use tools or machines until your reactions have returned to normal
Prolonged and painful erectionIf this lasts for more than four hours, you must contact a doctor straightaway

Important: if you get chest pains or suddenly have loss of vision, contact your doctor for medical attention straightaway.

If you experience any other symptoms which you think may be due to this medicine, discuss them with your doctor or pharmacist.

  • Keep all medicines out of the reach and sight of children.
  • Store in a cool, dry place, away from direct heat and light.
  • If you buy any medicines, check with a pharmacist that they are safe to take with your other medicines.
  • Never take more than the prescribed dose. If you suspect that someone has taken an overdose of this medicine, go to the accident and emergency department of your local hospital at once. Take the container with you, even if it is empty.
  • If you are having an operation or dental treatment tell the person carrying out the treatment which medicines you are taking.
  • This medicine is for you. Never give it to other people even if their condition appears to be the same as yours.
  • Never keep out-of-date or unwanted medicines. Take them to your local pharmacy which will dispose of them for you.
  • If you have any questions about this medicine ask your pharmacist.

Further reading & references

  • British National Formulary; 62nd Edition (Sep 2011) British Medical Association and Royal Pharmaceutical Society of Great Britain, London
  • Manufacturer's PIL, Viagra® 25 mg, 50 mg, 100 mg; Manufacturer's PIL, Viagra® 25 mg, 50 mg, 100 mg, Pfizer Limited, The electronic Medicines Compendium. Dated July 2010.

Disclaimer: This article is for information only and should not be used for the diagnosis or treatment of medical conditions. EMIS has used all reasonable care in compiling the information but make no warranty as to its accuracy. Consult a doctor or other health care professional for diagnosis and treatment of medical conditions. For details see our conditions.

Original Author:
Helen Allen
Current Version:
Peer Reviewer:
Dr John Cox
Document ID:
1490 (v24)
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