Aromatase inhibitors (anastrozole, exemestane and letrozole)

These three drugs, known as aromatase inhibitors, all work in a similar way to each other. This means they share many of the same side effects, although there are some differences.

For more detail, you can check the printed information that comes with your tablets. You can also download our individual factsheets on each drug from the publications box on the right hand side of the screen for more in-depth information.

More common side effects

• Hot flushes.
• Night sweats.
• Vaginal dryness or irritation.
• Loss of sex drive.

If you are experiencing any of these menopausal-like side effects such as hot flushes, night sweats or vaginal dryness then you may find it helpful to read our factsheet about managing menopausal symptoms.

• Joint pain.

Joint pain is a common side effect of anastrozole (Arimidex), letrozole (Femara) or exemestane (Aromasin). Sometimes this symptom will improve with time. If you are experiencing joint pain, discuss this with your GP, cancer specialist or breast care nurse who may be able to suggest ways to help such as taking anti-inflammatory pain relief.

• Reduced bone strength.

Treatment with an aromatase inhibitor reduces the amount of oestrogen in your body. A lack of oestrogen over time can increase the risk of osteoporosis (thinning of the bone). Before taking anastrozole (Arimidex), letrozole (Femara) or exemestane (Aromasin) you will usually be offered a scan to check the density of your bones and this may be repeated at regular intervals while you are having treatment.

For more information about changes to your bones, download or read our Osteoporosis and breast cancer booklet.

Less common side effects

• Nausea, vomiting or diarrhoea.
• Skin rash.
• Headache.
• Sleepiness.
• Hair thinning.
• Low mood or depression.

These symptoms tend to be mild and improve with time If the symptoms don’t improve, talk to your specialist.

Rare side effects

• Vaginal bleeding.

This can sometimes happen in the first few weeks after starting treatment. It usually occurs when switching from another type of hormone treatment. If the bleeding continues, it’s important to tell your specialist.