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What does it do?

Sildenafil is used to treat pulmonary hypertension (high blood pressure in the blood vessels of your lungs), and sometimes other conditions. It improves blood flow by relaxing your blood vessels.

If you are taking sildenafil for erectile dysfunction see separate information sheet "Sildenafil (for erectile dysfunction)".

Before you start

  • Tell your doctor if you have had a recent stroke, heart or blood pressure problems, or an eye problem called optic neuropathy.
  • Tell your doctor if you are pregnant, planning to become pregnant, or breastfeeding.
  • Do not use sildenafil if you are taking a nitrate medicine (e.g. glyceryl trinitrate or isosorbide mononitrate). Taking them both can cause a dangerous drop in blood pressure.

How should you take it?

Take sildenafil regularly as directed with a glass of water. You can take it with or without food.
Measure the liquid carefully with an oral syringe or measuring spoon. Shake the bottle well before measuring each dose.

What if you forget a dose?

If it is nearly time for your next dose, skip the missed dose and take your next dose at the usual time. Otherwise, take the missed dose as soon as you remember. Do not take two doses at the same time.

Can you take other medicines?

Some medicines available without a prescription may react with sildenafil including:

  • glyceryl trinitrate (GTN) (e.g. Nitrolingual®, Glytrin®)

Tell your pharmacist or doctor about all medicines or treatments that you may be taking, including vitamins, herbal products (e.g. St John's wort) or recreational drugs.

What side effects might you notice?

Side EffectsRecommended action

Prolonged erection (longer than four hours)

Changes in vision

Tell your doctor immediately

Headache, dizziness


Runny or blocked nose

Muscle aches and pains


Tell your doctor if troublesome

If you notice any other effects, discuss them with your doctor or pharmacist.

Other information:

  • Grapefruit, grapefruit juice or sour/Seville oranges may react with sildenafil. Discuss with your pharmacist.
  • Store sildenafil liquid as directed. Discard any leftover liquid after the expiry date on the bottle – ask your pharmacist how to do this safely.
  • Do not stop taking sildenafil without talking to your doctor first.

This leaflet contains important, but not all, information about this medicine.

Prepared by the MyMedicines Committee at Christchurch Hospital, Te Whatu Ora - Waitaha, New Zealand. March 2023

For more general information about this sheet and its contents, see: What does a My Medicines sheet cover?

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About My Medicines

My Medicines Patient Information Leaflets (PILs) contain important, but not all, information about the medicines they describe.

For more information about the sheets, see: What does a My Medicines sheet cover?

My Medicines is developed by a team at Te Whatu Ora – Waitaha. Our team is made up of doctors, pharmacists, and a non-medical person to help us keep to plain language. We also discuss our information with specialist health professionals or groups when needed