What does sildenafil do to your body?

Sildenafil treats erectile dysfunction by increasing blood flow to the penis during sexual stimulation. This increased blood flow can cause an erection. Sildenafil treats PAH by relaxing the blood vessels in the lungs to allow blood to flow easily.

1. About sildenafil

Sildenafil is a medicine used to treat erectile dysfunction. 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 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 will not cause an erection. You need to be aroused for it to work.
  • The most common side effects are headaches, 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 is not 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 like 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 doctor. 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.

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.


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