Sildenafil is a medicine used to treat erection problems (erectile dysfunction).
Sildenafil is also sometimes used to treat pulmonary hypertension (high blood pressure in the blood vessels that supply the lungs).
If you have erection problems sildenafil works by temporarily increasing blood flow to your penis when you get sexually excited.
In pulmonary hypertension it works by relaxing blood vessels in the chest.
If you buy sildenafil for erectile dysfunction, it can also be known by the brand names Viagra, Aronix, Liberize and Nipatra.
Sildenafil for pulmonary hypertension can also be known by the brand names Revatio and Grandipam.
This medicine is available on prescription and you can also buy it from most pharmacies. It comes as standard tablets, chewable tablets, and as a liquid that you swallow.
Key facts
- It usually takes 30 to 60 minutes for sildenafil to work for erectile dysfunction. You can take it up to 4 hours before you want to have sex.
- Taking sildenafil alone will not cause an erection. You need to be sexually excited for it to work.
- The most common side effects are headaches, feeling sick, indigestion and dizziness. Many people have no side effects or only mild ones.
- It can be dangerous to take sildenafil if you also take medicines called nitrates (often given for chest pain). The combination can cause a dangerous fall in your blood pressure. If you’re not sure if you’re taking a nitrate, ask your doctor or pharmacist.
- Do not drink grapefruit juice if you’re taking sildenafil (Revatio) for pulmonary hypertension. It affects the way the medicine works.
Who can and cannot take sildenafil
Who can take sildenafil
Most men aged 18 and over can take sildenafil for erectile dysfunction.
Most adults and children aged 1 year and over can take sildenafil for pulmonary hypertension.
Who may not be able to take sildenafil
Sildenafil is not suitable for some people. To make sure it’s safe for you, speak to your doctor or pharmacist before taking sildenafil if you:
- have ever had an allergic reaction to sildenafil or any other medicine
- are taking medicines called nitrates for chest pain (angina)
- have a serious heart or liver problem
- have recently had a stroke, heart attack or a heart problem – your doctor should carefully check whether your heart can take the additional strain of having sex
- have low blood pressure (hypotension)
- have a rare inherited eye disease, such as retinitis pigmentosa
- have sickle cell anaemia (an abnormality of red blood cells), leukaemia (cancer of blood cells) or multiple myeloma (cancer of bone marrow)
- have a deformity of your penis or Peyronie’s disease (curved penis)
- have a stomach ulcer
- have a bleeding problem like haemophilia
How and where to get sildenafil
On the NHS
You can get sildenafil on the NHS if you have erectile dysfunction or pulmonary hypertension.
Branded versions of sildenafil such as Viagra are not available on the NHS, except in special circumstances.
Private prescription
You can also get sildenafil on a private prescription from your doctor. This means you’ll need to pay the full cost of the medicine.
From a pharmacy
You can buy sildenafil from a pharmacy after a discussion with the pharmacist.
They’ll ask you some questions about your general health to make sure sildenafil is safe for you to take. You can also talk to them about side effects.
If the pharmacist has any concerns about whether sildenafil is safe for you, they may advise you to see your doctor.
Online
You can buy sildenafil over the internet. Be very careful if you do this as many websites sell fake medicines.
Online medicines are not always regulated and the ingredients in them can vary from one pack to another. They can cause unpleasant side effects or may not be suitable for you.
It’s best to see your doctor before buying medicines online. They know your medical history and can discuss whether you might benefit from treatment.
If you choose to buy sildenafil over the internet, make sure:
- any online pharmacy is registered with the General Pharmaceutical Council (GPhC)
- any online doctor service is registered with the Care Quality Commission (CQC)
- all doctors are registered with the General Medical Council (GMC)
How and when to take sildenafil
It’s important to take sildenafil as advised by a doctor or pharmacist.
Dosage and strength for erectile dysfunction
Sildenafil tablets for erectile dysfunction come in different strengths ranging from 25mg to 100mg.
The usual dose is 50mg, when you need it. Do not take it more than once a day.
The dose can be increased to 100mg or decreased to 25mg depending on its effect.
Take sildenafil up to 4 hours before you want to have sex. For sildenafil to work properly, you’ll need to be sexually excited.
Dosage and strength for pulmonary hypertension
Sildenafil tablets for pulmonary hypertension come in 10mg and 20mg strengths.
The usual adult dose is 20mg taken 3 times a day.
Doses for children can range from 10mg to 20mg taken 3 times a day, depending on their weight. Do not take it more than 3 times a day.
How to take tablets
Swallow tablets whole with a drink of water or juice (but not grapefruit juice).
For erectile dysfunction, it’s best to take sildenafil on an empty stomach. It may take longer to work if you take it with food.
How to take liquid
If you or your child are taking sildenafil as a liquid, 1ml is usually the same as taking a 10mg tablet, but it’s important to always check the medicine label.
Liquid sildenafil will usually be made up for you by your pharmacist.
The medicine will come with a plastic syringe or spoon to help you take the right amount. If you do not have a plastic syringe or spoon, ask your pharmacist for one. Do not use a kitchen teaspoon as it will not measure the right amount.
If you forget to take it
If you have pulmonary hypertension and you forget to take a dose of sildenafil, take it as soon as you remember unless it’s nearly time for your next dose. In this case, just leave out the missed dose and take your next dose at the usual time.
Never take 2 doses at the same time. Never take an extra dose to make up for a forgotten one.
If you often forget doses, it may help to set an alarm to remind you. You could also ask your pharmacist for advice on other ways to help you remember to take your medicine.
If you take too much
Taking too much sildenafil can cause unpleasant side effects.
Talk to your doctor if you take too much sildenafil and you’re worried about any of these side effects:
- headaches
- dizziness
- indigestion
- blocked nose
- changes to your vision