What it is used for

Hormone receptor positive breast cancer after the menopause

Read our guides:

Polycystic ovary syndrome (PCOS)

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.

Helping ovulation in polycystic ovary syndrome (PCOS), as a fertility treatment
Breast cancer in men or before the menopause, alongside other treatment

How it works

Letrozole blocks an enzyme called aromatase, which makes oestrogen in the body after the menopause. Some breast cancers need oestrogen to grow, so lowering it slows or stops them. In fertility treatment, a short course triggers the brain to release hormones that help an egg develop.

Side effects

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

Common side effects

hot flushes
joint pain or stiffness
feeling tired
sweating
headache
weight gain
thinning hair

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:

sudden pain or swelling in your leg, chest pain or breathlessness, which can be signs of a blood clot
signs of a stroke or heart attack. Call 999

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

It can thin your bones. You may have bone density scans and be advised to take calcium and vitamin D.

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.