NZ Formulary

Sildenafil (for erectile dysfunction)


What does it do?

Sildenafil is used to treat erectile dysfunction (trouble getting or keeping an erection).

How should you take it?

Take sildenafil with a glass of water, about one hour before having sex, or as directed. You can take it with or without food.
It may keep working for up to 4 hours.
Do not take more than one dose a day.

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.

Important information continues on next page.

Other information:

  • Tell your doctor if you have had a recent stroke, heart or blood pressure problems, or an eye problem called optic neuropathy.
  • Don’t 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.
  • Grapefruit, grapefruit juice or sour/Seville oranges may react with sildenafil. Discuss with your pharmacist.