Sildenafil (Viagra)

1. About sildenafil

Sildenafil is a medicine used to treat erectile dysfunction (sexual impotence). It increases blood flow to the penis to help men get an erection. At least two-thirds of men have improved erections after taking it.

Sildenafil is also sometimes used (in men and women) to treat pulmonary hypertension (high blood pressure in the blood vessels that supply the lungs).

This medicine is available on prescription and can also be bought from most pharmacies. It comes as tablets that you swallow, chewable tablets and as a liquid that you drink.

2. 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 won't cause an erection. You need to be aroused for it to work.

The most common side effects are headache, feeling sick, hot flushes and dizziness. Many men 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.

Sildenafil is called by the brand names Viagra (for erectile dysfunction) and Revatio (for pulmonary hypertension).

3. Who can and can't take sildenafil

Sildenafil for erectile dysfunction (Viagra) can be taken by men aged 18 and over. It's not for women or children.

Sildenafil for pulmonary hypertension (Revatio) can be taken by adults and children aged 1 and over.

Sildenafil isn't suitable for some people.

Do not take sildenafil if you:

  • have had an allergic reaction to sildenafil (viagra) or any other medicines in the past
  • are taking medicines called nitrates for chest pain
  • have a serious heart or liver problem
  • have recently had a stroke or a heart attack
  • have low blood pressure
  • have a rare inherited eye disease, such as retinitis pigmentosa

Check with your doctor before taking sildenafil if you:

  • 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 heart problem - your doctor should carefully check whether your heart can take the additional strain of having sex
  • have a stomach ulcer, or a bleeding problem (such as haemophilia)

4. 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 GP.

This means you'll need to pay the full cost of the medicine. Prices vary, but on average 4 tablets costs around £20.

From a pharmacy

You can buy sildenafil from a pharmacy following a discussion with the pharmacist. To make sure sildenafil is safe for you to take, they'll ask you some questions about your general health. 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 GP.

Online

You can buy sildenafil/Viagra over the internet. Be very careful if you do this as many websites sell fake medicines.

Online medicines aren't 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 GP before buying medicines online. They know your medical history and can discuss whether you might benefit from treatment.

If you choose to buy sildenafil/Viagra over the internet, ensure that:

5. How and when to take it

Sildenafil is a prescription medicine. It's important to take it as advised by your doctor.

How much will I take 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 (no 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.

How much will I take for pulmonary hypertension?

Sildenafil tablets for pulmonary hypertension come in 10mg and 20mg tablets.

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.

How to take it

Swallow tablets whole with a glass of water or juice (but not grapefruit juice).

For erectile dysfunction, it's best to take sildenafil on an empty stomach. If you take it with food it may take longer to work.

Liquid sildenafil

If you or your child are taking sildenafil as a liquid, 1ml is usually the same as taking a 10mg tablet.

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 don't have a plastic syringe or spoon, ask your pharmacist for one. Do not use a kitchen teaspoon as it won't give the right amount.

What if I 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 and then continue as usual.

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.

What if I take too much?

Taking too much sildenafil by accident can cause unpleasant side effects such as:

  • headache
  • dizziness
  • indigestion
  • blocked nose
  • altered vision

Talk to your doctor if you've taken too much sildenafil and you're worried about these side effects.

6. Side effects

Like all medicines, sildenafil can cause side effects in some people. Many people have no side effects or only minor ones.

Common side effects

Common side effects happen in more than 1 in 100 people. If you get these side effects, keep taking the medicine, but tell your doctor or pharmacist if these side effects bother you or don't go away:

  • headache
  • feeling sick
  • hot flushes, including facial flushing
  • indigestion
  • a colour tinge to your vision or blurred vision
  • stuffy nose
  • dizziness

Serious side effects

Serious side effects are rare and happen in less than 1 in 1,000 people.

Stop taking sildenafil and tell a doctor straight away if you get:

  • chest pains - if this happens during or after sex, get into a semi-sitting position and try to relax, do not use nitrates to treat your chest pain
  • prolonged and sometimes painful erections - if you have an erection which lasts for more than 4 hours, contact a doctor immediately
  • a sudden decrease or loss of vision
  • a serious skin reaction - symptoms may include fever, severe peeling and swelling of the skin, blistering of the mouth, genitals and around the eyes
  • seizures

Serious allergic reaction

In rare cases, it's possible to have a serious allergic reaction to sildenafil.

Contact a doctor straight away if:

  • you get a skin rash that may include itchy, red, swollen, blistered or peeling skin
  • you're wheezing
  • you get tightness in the chest or throat
  • you have trouble breathing or talking
  • your mouth, face, lips, tongue or throat start swelling

These are warning signs of a serious allergic reaction. A serious allergic reaction is an emergency.

These are not all the side effects of sildenafil. For a full list see the leaflet inside your medicines packet.

You can report any suspected side effect to the UK safety scheme.

7. Pregnancy and breastfeeding

Sildenafil is not recommended in pregnancy and while breastfeeding.

Tell your doctor if you're:

  • trying to get pregnant
  • pregnant
  • breastfeeding

8. Cautions with other medicines

Some medicines don't mix well with sildenafil.

Tell your doctor if you're taking these medicines before you start sildenafil:

  • nitrates for chest pain
  • riociguat for pulmonary hypertension
  • recreational drugs called poppers - such as amyl nitrite

Mixing sildenafil with herbal remedies and supplements

Some complementary therapies may have ingredients that could interfere with sildenafil and cause side effects.

Important

Tell your doctor or pharmacist if you are taking any other medicines, including herbal remedies, vitamins or supplements.

9. Common questions

How does sildenafil work?

Sildenafil belongs to a group of medicines called phosphodiesterase 5 (PDE5) inhibitors.

It works if you have erection problems by temporarily increasing blood flow to the penis when you get sexually excited.

It works in pulmonary hypertension by relaxing blood vessels in the chest. This increases the blood supply to the lungs and reduces the workload of the heart.

How well does it work for erection problems?

Sildenafil works well for erectile dysfunction. In general, at least two-thirds of men say they have harder erections after taking it.

If sildenafil doesn't work for you, it may be because:

  • you haven't waited long enough after taking it before trying to have sex
  • you have waited too long after taking it to have sex
  • the dose isn't high enough
  • you're not sexually aroused enough
How long does it take to work?

Sildenafil usually starts to work within 30 to 60 minutes. It's triggered by sexual stimulation, so you need to be aroused for it to work.

How long will it work for?

You should be able to get an erection at any time between 1 and 4 hours after taking sildenafil.

Your erection should go away after you have had sex.

Can I take it as often as I want?

If you're taking sildenafil for erectile dysfunction, don't take it more than once a day.

If you're taking sildenafil (Revatio) for pulmonary hypertension, don't take it more than 3 times a day.

Is it safe to take it for a long time?

Sildenafil is safe to take for a long time. There don't seem to be any lasting harmful effects from taking it for many months and years.

Are there any other medicines that can improve erections?

If sildenafil doesn't work, there are other tablets you could try which work in a similar way, such as:

  • tadalafil (Cialis) - can be taken up to 36 hours before sex
  • avanafil (Spedra) - can be taken up to around 4 hours before sex
  • vardenafil (Levitra) - can be taken up to around 4 hours before sex

You could also try a medicine called alprostadil. This is a man-made hormone that helps to stimulate blood flow to the penis.

Alprostadil comes as:

  • an injection directly into your penis
  • a small pellet placed inside your urethra (the tube that carries urine from your bladder to the tip of your penis)

If you can't get erections because of a hormonal problem, your GP may refer you to an endocrinologist (who specialises in the treatment of hormonal problems).

You may benefit from treatment using injections of man-made hormones to restore your hormone levels to normal.

Are there non-medical options for erectile dysfunction?

Non-medical treatments for erectile dysfunction include:

  • vacuum pump
  • psychological treatments
  • penile implants
  • pelvic floor muscle exercises

Some complementary therapies, such as acupuncture, have claimed to treat erectile dysfunction. However, there's little evidence they work.

Is there a herbal Viagra?

There are lots of treatments that claim to be a 'herbal Viagra'. In fact, there's no such thing. A herbal Viagra has never been approved as a treatment for erectile dysfunction. Plus, these treatments may be fake or unsafe.

Can women use it?

Women can use sildenafil for pulmonary hypertension.

There's no good evidence that sildenafil works for women with sexual problems.

Can I drink alcohol with it?

A beer or a couple of glasses of wine aren't likely to stop or delay sildenafil working. But drinking lots of alcohol can make it more difficult to get an erection. To get the most benefit from sildenafil, don't drink heavily before taking it.

Will recreational drugs affect it?

Taking poppers (amyl nitrite) with sildenafil can have a dangerous effect on your heart.

It can also be potentially dangerous to take sildenafil with:

  • stimulants like MDMA (ecstasy) or cocaine
  • hallucinogens like LSD
  • novel psychoactive substances (which used to be known as legal highs) like mephedrone

Sildenafil hasn't been properly tested with recreational drugs. Talk to your doctor if you think you might use any recreational drugs with sildenafil.

Is there any food or drink I need to avoid?

Don't drink grapefruit juice if you are taking sildenafil (Revatio) for pulmonary hypertension. It interferes with the way the medicine works.

You can eat and drink normally while taking sildenafil (Viagra) to get an erection.

Any lifestyle tips for erectile dysfunction?

Erectile dysfunction can often be improved if you make changes to your lifestyle, such as:

Page last reviewed: 07/07/2017
Next review due: 07/07/2020