Disclaimer

Although we take care to ensure accuracy, Macmillan Cancer Support does not accept liability for the information and materials provided or referenced in Ask an Expert or for any errors or omissions in them, or for third-party information or services such as other websites we may link to. The information and materials provided or referenced in Ask an Expert are for information purposes only and are not intended to be legal, financial or medical advice or opinions. If you need more details on your rights, please contact a financial, legal or other appropriate adviser.

We recommend that you consult your doctor if you are concerned about your health. Any You should not rely on any information and materials provided or referenced in Ask an Expert including by our Experts as they are not a replacement for advice, diagnosis or treatment from your medical team, and our Experts cannot provide a second opinion to that of your medical team.

Your question can be read by others – so please don't post your contact details or any other information that could personally identify you. Please read our Terms and Conditions and Community Guidelines for more details.

Letrozole and scary mood swings

Kalulu
  • 1 reply
  • 44 subscribers
  • 1038 views

I had a lumpectomy about 2 months ago (clear margins and nodes) and have been on Letrozole for 3 weeks. I start radiotherapy in 3 weeks time. I'm OK, apart from not sleeping (average about 4 hours on a good night) and having developed quite frightening mood swings - they're really impacting on my life - I am so angry and wound up all the time I scare myself - and also my husband and the dog! I'm ashamed to feel this way, especially when so many people are so much worse off than I am. I doubt very much if I'd get a GP appointment and the hospitals where I got my surgery and will get my radiotherapy are a 30 mile and 90 mile round trip respectively, so I can't just drop in to see a BC nurse.  I get lots of exercise and eat a healthy diet and I don't recognise the person I am at the moment. Is there anything I can do to mitigate the mood swings and maybe get a decent nights sleep? 

  • Hi Kalulu

    Thank you for getting In touch via our online community here at Macmillan. My name is George, and I am one of the Cancer Information Nurse Specialists on the Macmillan Support Line.

    I'm sorry to hear about the difficulties and side effects you are experiencing since starting your letrozole treatment. Side effects associated with low mood and sleep disturbances can be common and massively impact one's quality of everyday life. 

    Medication side effects often improve over time, but new, continuing, or worsening symptoms should be discussed as soon as possible with either your treating team or GP. They can assess and sometimes modify the treatment or recommend different times to take the medication, which may reduce the severity of the symptoms. Early discussion can help manage side effects better. 

    Low mood and mood changes can be one of this treatment's most concerning side effects. Mood changes occur due to changes in the sex hormones within the body. Relaxation, as well as mindfulness meditation, can be very effective. Still, people may sometimes need a small dose of medication to treat anxiety and low mood to help with the more severe side effects.  

    Difficulty sleeping can have an impact on other areas of your life. Mindfulness, meditation and complementary therapies can be helpful in this situation. It sounds like you are already actively trying many things we recommend, such as exercise and diet. Some medications may help you rest and develop a more natural pattern and are worth discussing with your GP or treating team. 

    It may also be worth contacting Breast Cancer Now as they are in an ideal position to give further advice regarding your concerns. Free specialist counselling can also be accessed via Macmillan.

Help us do whatever it takes, because we’ve never been needed more.

© Macmillan Cancer Support 2025 © Macmillan Cancer Support, registered charity in England and Wales (261017), Scotland (SC039907) and the Isle of Man (604). Also operating in Northern Ireland. A company limited by guarantee, registered in England and Wales company number 2400969. Isle of Man company number 4694F. Registered office: 3rd Floor, Bronze Building, The Forge, 105 Sumner Street, London, SE1 9HZ. VAT no: 668265007