Breast Cancer – Side Effects of Letrozole (Femara)

letrozoleI was diagnosed with breast cancer. After surgery, chemotherapy and radiotherapy, I was prescribed Letrozole (Femara) and must take one 2.5mg tablet each day for a perios of 5 years. Letrozole is a hormonal therapy drug. It is used to treat breast cancer in women who have been through the menopause. Letrozole has been prescribed in order to reduce the liklihood of the cancer recurring, so I am taking it. However, Letrozole does have many unpleasant side-effects and I suffer with most if them. I was not told about these. I think I should have been.

Letrozole is used after surgery and other treatments to reduce the risk of breast cancer coming back. You will usually take it for a few years. Doctors sometimes prescribe it before or after you have another type of hormonal therapy drug. Sometimes doctors give letrozole before surgery to try to reduce the size of the cancer and avoid having a mastectomy (removal of the breast). Letrozole is also used to control breast cancer that has spread to other parts of the body (secondary breast cancer)

Many breast cancers rely on the hormone oestrogen to grow. This type of breast cancer is called oestrogen receptor-positive (ER positive) breast cancer. My breast cancer fell into this category.

Hormones are substances produced naturally in the body. They act as chemical letrozole-tabletsmessengers and help control the activity of cells and organs. Hormonal therapies interfere with the way hormones are made or how they work in the body. After the menopause, oestrogen is no longer made in the ovaries. Instead it’s made in the fatty tissues of the body. This happens when an enzyme called aromatase changes other hormones into oestrogen. Letrozole is a drug called an aromatase inhibitor. It blocks this process and reduces the amount of oestrogen in the body.


I will explain the most common side effects of letrozole here but it is sensible to tell your doctor or nurse about the side effects you have. They can prescribe drugs to help control some of them and give you advice about managing them.

Hot flushes and sweats

These are common and are often mild, but this can vary. Hot flushes and sweats may lessen after the first few months. Cutting down on nicotine, alcohol and hot drinks containing caffeine, such as tea and coffee, can help. Dress in layers, so you can remove clothes as needed. Natural fabrics, such as cotton, may feel more comfortable. If hot flushes are troublesome, tell your doctor. Low doses of certain antidepressant drugs can help to reduce flushes.

Bone thinning

Taking letrozole for a few years increases your risk of bone thinning, called osteoporosis. This can increase your risk of a broken bone (fracture). You will usually have a bone density scan to check your bone health before and during treatment. If you are at risk of osteoporosis, your doctor may prescribe drugs called bisphosphonates to protect your bones. They will also usually advise you to take calcium and vitamin D supplements. Regular walking, eating a healthy diet, not smoking and sticking to sensible drinking guidelines will also help to strengthen your bones.

Tiredness and lack of energy

You may feel tired, sleepy or feel like you have no energy when you start taking letrozole. Try to pace yourself until this improves. It is important to get the right balance of having enough rest and being physically active. Regular short walks will help you to feel less tired. If you feel sleepy, don’t drive or operate machinery.

Joint and muscle pain

You may have pain and stiffness in your joints, and sometimes in your muscles, while taking letrozole. Let your doctor or nurse know if this happens. They can prescribe painkillers and give you advice. Being physically active and maintaining a healthy weight can help reduce joint pain and keep them flexible. Let your doctor know if it doesn’t get better.

Feeling sick and indigestion or tummy pain

Any sickness is usually mild, but let your doctor or nurse know if this happens. Letrozole may also cause indigestion or tummy pain. Let them know if you have any of these symptoms. They can prescribe drugs to help.

Change in appetite

If you do not have much appetite, try eating small meals often and regularly. If problems with eating don’t get better talk to your doctor or nurse. Some women find their appetite increases. Eating healthily and being physically active will help if you have concerns about your weight, but staying active when you are tired and have joint and muscle pain can be difficult.

Hair thinningletrozole-hair

Some women notice that their hair becomes thinner while taking letrozole. This is usually mild. Your hair will get thicker after treatment finishes. I hope this is true. The hair thinning is quite embarrassing for a woman.

Skin rashes

You may get a mild skin rash . Tell your doctor or nurse if this happens. It is very important to contact your doctor straightaway if you get a severe skin rash.

Mood and behaviour changes

Some women may find they have a low mood while taking letrozole. Or you may have problems concentrating, feel anxious or have difficulty sleeping. Talk to your nurse or doctor if you have these changes so they can give you support and advice.


If you have headaches let your doctor or nurse know. They can usually be controlled with painkillers you can buy yourself.

Feeling dizzy

Letrozole may cause dizziness. Let your doctor or nurse know if this is a problem.

Weight gain

You may put on weight when you’re taking hormonal therapy. Eating healthily and being physically active can help to keep you to a healthy weight: however, it is difficult to be physically acive when you also have the side effects of tiredness or joint and muscle pain.

Vaginal bleeding

Letrozole rarely causes vaginal bleeding. If this happens it is most likely in the first few weeks of treatment, or when you change from another hormonal therapy to letrozole. If bleeding continues for more than a few days, tell your doctor or nurse.

Raised blood pressure

Tell your doctor or nurse if you have ever had any problems with your blood pressure. Your nurse will check it regularly during your treatment. This is one of the few side-effect I do not get!

Raised cholesterol level

Your doctor may check your cholesterol levels with a blood test.

Build-up of fluidletrozole-fluid

You may get swollen feet and ankles because of fluid building up. If you notice this or any other swelling let your doctor know.


In addition to these more common side-effects of Letrozole, there are other possible side-effects that are less common.

Vaginal dryness

Non-hormonal creams and gels or lubricants can help reduce dryness and discomfort during sex. You can buy these at a chemist or your doctor can prescribe them.

Urine infection

Let your doctor know if you have pain or discomfort when you pass urine, or if you need to go more often, or your urine is cloudy or smelly. Drink lots of fluids if you think you may have an infection.

Eye problems

Occasionally women get sore eyes or blurry vision with letrozole. Always tell your doctor or nurse if you notice any change in your vision.

Changes to your heartbeat

If you notice changes to your heartbeat, such as it speeding up, let your doctor know. If you have pain or tightness in your chest, or feel breathless at any time during or after treatment, see a doctor straightaway.


I was told that my side-effects would settle down after a few months. That has not been the case for me, nor ofr many other women who have contacted me. Still, we keep taking the tablets. I would rather complain than have to explain to my family that the breast cancer is back.

Valerie Penny




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