What it is used for

Erectile dysfunction (some strengths available from pharmacies)
Pulmonary arterial hypertension (high blood pressure in the lungs) (Revatio)

Off-label uses

Doctors sometimes prescribe a medicine for a condition it is not officially licensed for. This is called off-label use. It is legal and common when there is good evidence it helps, and your doctor should explain why they are suggesting it.

Raynaud's phenomenon, under a specialist

How it works

Sildenafil blocks an enzyme called PDE5. This relaxes blood vessels in the penis so more blood can flow in when you are sexually aroused. In the lungs, it relaxes blood vessels and lowers pressure.

Side effects

Like all medicines, Sildenafil can cause side effects, although not everyone gets them. Many are mild and ease after the first few weeks.

Common side effects

headache
flushing
indigestion
a blocked nose
dizziness
changes in colour vision

Tell your doctor or pharmacist if these bother you or do not go away.

Serious side effects

These are rare. Call 111 or contact your doctor straight away if you get:

an erection lasting more than 2 hours. Go to A and E
chest pain during or after sex. Stop and call 999
sudden loss of vision or hearing

Call 999 if you have signs of a serious allergic reaction, such as swelling of your lips, mouth, throat or tongue, or trouble breathing.

You can report any side effect to the Yellow Card scheme, run by the medicines regulator.

Stopping and withdrawal

Important safety information

Never take it with nitrates such as GTN spray or isosorbide, or recreational "poppers". Blood pressure can drop dangerously.
Not suitable if your doctor has advised against sex because of heart problems.
Erection problems can be an early sign of heart disease or diabetes. See a GP.

Questions about your medicine?

A pharmacist can answer questions about your medicines for free, without an appointment. You can also ask your GP for a medication review. Check if you can get free prescriptions.