Like any drug, letrozole can cause side effects. Everyone reacts differently to drugs and some people have more side effects than others. 

Common side effects of letrozole include:

Other side effects of letrozole include:

Coping with side effects of letrozole

For many people, side effects improve within the first few months of starting the treatment. However, for some people they may cause distress and disrupt everyday life.  

If you have any side effects, whether they’re listed here or not, talk to your GP or treatment team. They may be able to offer ways of improving your symptoms. 

Your specialist may suggest changing to a different aromatase inhibitor such as anastrozole or exemestane, or another hormone treatment, as some women get on better with a different drug.  

Your breast care nurse may also be able to offer help and support. 

Common side effects 

Aching or pain in the joints and muscles 

Aching or pain in the joints and muscles is often mild and temporary, although for some people it’s more severe and longer lasting.

It can usually be relieved with mild pain relief like paracetamol or an anti-inflammatory drug such as ibuprofen. Before using anti-inflammatory pain relief, ask your doctor about the correct dose, how long you should use it for and any possible side effects, especially if you have a stomach ulcer or asthma. 

Exercise that gently stretches your joints or strengthens your muscles to better support your joints, such as yoga or pilates, may help improve your symptoms. A physiotherapist may also be able to suggest exercises to help. If you have secondary breast cancer, check with your specialist before starting any new type of exercise.

If the pain is severe, your specialist may refer you to a rheumatologist (a doctor who has a special interest in joint and muscle pain). It may also be helpful to see a pain management specialist at a pain clinic. 

Some people benefit from switching to a different hormone therapy. For example, it may be possible to switch to another aromatase inhibitor to see if your pain improves, or some people might be offered the drug tamoxifen as an alternative. 

Menopausal symptoms 

You may have menopausal symptoms such as hot flushes, sweating, sleep disturbance, vaginal irritation such as dryness and itching, and reduced libido (sex drive). Many people find that symptoms improve over time. 

Find out more about menopausal symptoms or sex and intimacy.

Low mood and depression 

Some people feel low or depressed. It can be difficult to know whether this is because of the medication or other reasons such as menopausal symptoms or dealing with the diagnosis of cancer. 

Talk to your GP or treatment team about how to manage a change in mood. Some people find counselling or mindfulness helpful. Others find exercise improves their mood. Your GP or specialist can refer you for counselling or may suggest you take an antidepressant drug. 

Your breast care nurse may also be able to offer support or tell you about support services in your area. 

Difficulty sleeping 

If you have difficulty sleeping (insomnia), some simple things like limiting caffeine in the afternoon and evening, keeping your room dark and quiet, and going to bed and getting up at a set time each day may help. 

Relaxation exercises can also be helpful. There are CDs, podcasts and phone apps that can guide you through these techniques. 

If your insomnia is persistent, your GP may prescribe something to help you sleep.

Fatigue (extreme tiredness)

Studies show that physical activity can help to relieve fatigue. Find out more about fatigue and how to manage it.

Complementary therapies are also helpful for some people. 

Some people report feeling sleepy when taking letrozole. 

Osteoporosis (thinning of the bone) 

Letrozole reduces the amount of oestrogen in the body. A lack of oestrogen over time can cause osteoporosis

Your specialist will sometimes check the strength and thickness of your bone (bone density) with a scan before or shortly after you start taking letrozole. 

Your bone density may be checked every two to three years while you’re taking letrozole, depending on the results from the initial scan or whether your specialist has any concerns. 

To help keep your bones healthy you can increase your intake of calcium and vitamin D. Most people do this by taking a supplement. You may also want to eat more foods that are rich in calcium, such as milk, cheese, yoghurt and cereals. For vitamin D, you can increase the amount of oily fish, mushrooms and eggs you eat.

Stopping smoking and doing regular resistance exercise can also help keep your bones strong. 

Find out more about looking after your bones.

If your bones are already beginning to show signs of thinning or if you already have osteoporosis, you may be given another drug to increase bone density and strength. This will usually be from a group of drugs called bisphosphonates. If you’re concerned about this you may find it helpful to speak to your specialist. 

High blood pressure (hypertension) and high cholesterol 

Letrozole can cause high blood pressure (hypertension) in some people. Your GP will be able to monitor and treat this if necessary. 

It may also cause the level of cholesterol in the blood to rise, although this doesn’t usually need treatment. If you have a history of high cholesterol you may want to discuss this with your specialist or GP.

Other side effects

Headaches, nausea and vomiting 

Letrozole can sometimes cause headaches, nausea and vomiting. 

These usually improve or become easier to manage over time. Mild pain relief such as paracetamol may help with headaches. Taking your letrozole with or after food can help reduce nausea.

Change of appetite 

If you lose your appetite, it may help to take your tablet with food. You may find eating small frequent meals or snacks helps keep up your food intake.  

If your appetite increases it may affect your weight. 

If you struggle to maintain a healthy weight, ask your GP or specialist about being referred to a dietitian. 

Find out more about diet and breast cancer treatment.

Constipation or diarrhoea 

If you have constipation or diarrhoea, it’s important to drink enough fluids. Keeping active and eating a high-fibre diet may help with constipation. 

Your GP or specialist can also prescribe medication to help with constipation or diarrhoea. 

Carpal tunnel syndrome 

Carpal tunnel syndrome causes pain, tingling, coldness or weakness in the hand. Speak to your GP or specialist if you have any of these symptoms. 

Hair and skin changes 

You may have some hair loss or thinning while taking letrozole. However, your hair should return to the way it was before treatment when you stop taking letrozole. A small number of women notice an increase in downy facial hair. 

Some people also report a skin rash.  

Vaginal bleeding 

Vaginal bleeding can happen in the first few weeks after starting letrozole. It most commonly occurs when changing from one hormone therapy to another. If the bleeding continues for more than a few days, tell your specialist. 

Dizziness 

Letrozole may cause dizziness. If you feel dizzy, avoid driving. If dizziness persists see your GP. 

Last reviewed: February 2019
Next planned review begins 2021

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