Side effects of hormone-blocking therapy

Hormone-blocking therapies are taken daily for 5 to 10 years. Different drugs have different side effects and you may experience some, or none, of these. 

Side effects are often only mild. For people who experience more severe issues, they usually ease over the first few months.

It can help to know that hormone-blocking therapies are very good at reducing the chance of early breast cancer coming back. This is why you've been advised to take them.

When to talk to your doctor about side effects

It is important that you do not stop taking hormone-blocking therapy without speaking with your doctor or nurse, as this may increase the risk of breast cancer returning.

Talk to your treating team as soon as your side effects become too much for you. Most side effects reduce over time, but your doctors may:

• change you to a different hormone-blocking drug. Each drug has different side effects. One drug may suit you better than another
• arrange a planned break from treatment
• give you advice on how best to manage your side effects.

Common side effects of hormone-blocking therapy

Many women experience menopausal-like symptoms when taking hormone-blocking (anti-oestrogen) therapies, especially tamoxifen. This is because tamoxifen blocks oestrogen receptors on healthy cells as well as breast cancer cells.

Normally, oestrogen enables healthy tissue, especially in the breast, vagina, brain, skin and bones, to continue to grow and stay healthy.

When drugs like Tamoxifen block oestrogen from entering healthy tissue, the side effects can be similar to menopause. We explain ways to reduce the common side effects:

• bone health issues
• joint pains or joint stiffness
• hair loss
• hot flushes
• eye problems such as redness, dryness and blurred vision
• fluid retention (‘oedema’)
• leg cramps
• mood swings, anxiety and depression
• nails thinning
• reduced sex drive (‘libido’)
• skin dryness
• vaginal dryness
• weight gain.

For information on managing side effects read Menopausal symptoms and breast cancer treatment.

Side effects of Aromatase Inhibitors (AIs)

Aromatase inhibitor medications are letrozole (Femara), anastrazole (Arimidex) and exemestane (Aromasin). They can cause your bones to become thin and weak.

Usually, your doctor will check your bone density before you start treatment to check for signs of osteoporosis. They use a simple test such as a DEXA scan. They may also check your vitamin D levels.

If your bones are already weak, you need help to protect from fractures. Doctors may prescribe:

• a bone strengthening drug such as a bisphosphonate, like Zometa, or
• a different hormone-blocking therapy instead, such as anti-oestrogen medication Tamoxifen.

You may experience joint pain (‘arthralgia’) and muscle pain (‘myalgia’) within weeks of starting to take an AI.

This can be mild or severe and sometimes happen with inflammation. Read about Joint pain related to breast cancer treatment.

Less common side effects of AIs

• increased blood cholesterol and lipid levels, which can increase your risk of developing heart problems
• joint and muscle pain that feels like Carpal Tunnel Syndrome (pain, tingling and numbness of the hand when the nerves through the wrist are compressed). In rare cases, AIs can cause Carpal Tunnel Syndrome.
• development of a ‘trigger finger’ (a condition where one of your fingers cannot straighten because the tendons tighten).

Side effects of Tamoxifen

Tamoxifen can slightly increase the risk of premenopausal women developing osteoporosis. However, if women are postmenopausal, tamoxifen slows down bone loss, decreasing the risk of osteoporosis.

Less common side effects of Tamoxifen

• endometrial changes. The lining of the uterus (‘endometrium’) can become thickened (‘hyperplasia’). You may need regular checks with your doctor or gynaecologist to monitor these changes. Rarely, endometrial hyperplasia may develop into endometrial cancer. If you have any abnormal vaginal bleeding or discharge, or unusual pelvic pain, contact your doctor or nurse immediately.
• blood clots. A deep vein thrombosis (DVT) in your leg, or a blood clot in your lung (pulmonary embolus) can develop. Contact your doctor immediately if you have any sudden shortness of breath, chest pain or pain in the calf.
• stroke. This rare side effect is caused by a blood clot in the brain. Seek urgent medical help if you have any symptoms or signs of a stroke, such as a sudden and severe headache, altered conscious state, numbness or weakness in arms or legs, or difficulty speaking.
• eye problems. You may experience blurred or reduced vision and damage to the retina (‘retinopathy’). Cataracts can develop with long-term use. Have regular checks with an eye specialist so they can treat any vision changes promptly.

Long-term side effects of hormone-blocking therapy

Read Menopause symptoms and breast cancer treatment. It details the common side effects and things you can try to reduce their impact on your life and wellbeing.

You can also keep a record of your side effects in BCNA’s My Journey side effects tracker. Tracking your physical and emotional symptoms can identify what might make the side effects worse. You can take this record to appointments, to help your doctors understand the impact and find the best ways to manage your situation.

Medications and supplements that affect hormone-blocking therapy

Some common medications can make hormone-blocking therapies less effective.

It’s important to talk to your doctor if you are taking, or plan to start:

• any other drugs such as anti-depressants
• herbal medicines, for example St John’s Wort
• complementary medicines.

If you are taking another medication, do not stop taking it without talking to your doctor.

Read more about complementary therapies in Complementary therapies and breast cancer.

Resources

We have many resources to help you reduce the impact of hormone-blocking treatments.

Video: Hormone-blocking therapy - is it worth it?

Video: Menopause – It's more than a hot flush! – Ask the Expert series, with Dr Tonia Mezzini

Podcast: Hormone Blocking Therapy – Balancing Quality of Life and Risk of Recurrence

Podcast: The Impact of Breast Cancer on Sexual Health: Physical Changes, Lubrication, Pleasure and Libido

Podcast: Sexual wellbeing after breast cancer

Video: Managing side effects of hormone-blocking treatment – Ask the Expert series, with Dr Michelle White

Read BCNA's article about Bone health and metastatic breast cancer.

Read BCNA's article on Managing symptoms and side effects of metastatic breast cancer.

Booklet: Breast cancer and sexual wellbeing

Factsheet: Bone health and breast cancer