Letrozole brain fog and insomnia

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I had a mastectomy in September 2025, it went smoothly and I didn’t need radiotherapy or chemotherapy. I had a hemicolectomy in June 2024 and I had a good recovery from that too. I also had an incisional hernia repair which went well.

I was fine after all that but once I started Letrozole, I have suffered the hot flushes, causing sleep disturbance, and whereas I was always good at sleeping, I now have insomnia. Despite being tired last night, I didn’t sleep until 5a.m. I am irritable and angry about things that have long since gone. I am frustrated because I can’t concentrate and forget things in a short space of time. This is no life. I woukd rather have another mastectomy and not take this Letrozole, it’s a vicious tablet! My doctor has prescribed Clonidine to reduce the hot flushes and it has had some effect on the hot flushes but not on the brain fog and inability to sleep. Can I stop taking it? Life feels like it’s not worth living

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Hi @biddy2

Thank you for posting. It sounds like a difficult time for you at the moment. You may want to call our helpline to talk this through. The helpline team have time to listen, talk things through and signpost you to additional support and information.

We speak to many people who experience side effects from hormone therapies, such as letrozole, and you’re not alone in finding they are causing a significant impact on your quality of life.

If you haven’t done so already, is it important to talk to your breast care nurse or treatment team again about how you’re feeling so they can support you. Deciding to stop hormone therapy can be a difficult decision and you’re treatment team will be best placed to discuss this with you. Sometimes they may recommend stopping the treatment temporarily to see if the symptoms resolve and then consider an alternative hormone therapy, such as tamoxifen, if appropriate. However, sometimes the negative impact on a person’s wellbeing may outweigh the benefit from taking the treatment. Your team will help you make a decision that is right for you.

You may find our information about managing brain fog (cognitive impairment) and trouble sleeping helpful. We also have a FaceBook Live session about managing sleep disturbance. You may want to task your treatment team or GP to refer you to a menopause specialist to help manage the menopausal symptoms you have. You can also speak to them about complimentary therapy which some people also find helpful.

We offer a range of free supportive services which you may be interested in. They include face to face and online courses and events. Our Moving Forward resources that are for people who have had a diagnosis of primary breast cancer and have come to the end of their main hospital treatment within the last 2 years, may be of particular interest. They include our Moving Forward booklet and Moving Forward courses

Do call our helpline if you would like to talk this through or have any further questions. Your call will be confidential, and the number is free from UK landlines and all mobile networks.

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Best wishes,

Cassie

Breast Care Nurse

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