Letrozole

What is letrozole?

Letrozole is a prescription-only medicine belonging to a group of drugs known as aromatase inhibitors that lower oestrogen levels. It is primarily used to treat hormone-dependent breast cancer in postmenopausal women. The common branded version of letrozole is Femara[1]. 

What is letrozole used for?

Letrozole is primarily used to treat hormone-dependent breast cancer in postmenopausal women or as an adjuvant treatment in hormone-receptor positive or hormone-dependent breast cancer. Under specialist advice, it can sometimes be used to treat breast cancer in men, or in women who have not reached the menopause, but this would be off-label as the manufacturer has not licensed its use for these conditions. It can also be used for fertility issues, under the care of a specialist, such as ovulation problems in women with conditions like polycystic ovary syndrome (PCOS) – although this is also an off-label use[1]. 

How does letrozole work?

Letrozole works by reducing the amount of oestrogen in the body. It does this by blocking an enzyme called aromatase, which normally converts androgens into oestrogen. Since some breast cancers grow in response to oestrogen, lowering oestrogen levels helps to slow or stop their growth and spread, improving the condition over time[1]. 

Who can take letrozole?

Letrozole can be taken by postmenopausal women with hormone-dependent breast cancer[1]. 

However, it is usually not suitable for premenopausal women, as this would be off-label and outside the medicines licensed conditions. It’s also not safe for people who are pregnant or breastfeeding as may affect the baby, or anyone who is allergic to letrozole or any of its ingredients[1]. 

Please tell your doctor or pharmacist about any conditions you may have before you start treatment and always follow the instructions in the Patient Information Leaflet[2]. 

How do you take letrozole?

Letrozole should be taken at the same time every day, with or without food, by swallowing the tablet whole with a drink of water. Always follow your doctor’s instructions[1]. 

What is the typical dosage of letrozole?

The standard dose of letrozole for breast cancer is 2.5mg once daily. Your doctor will advise you on the exact dose and duration based on your condition, especially for off-label use[1]. 

Can you stop taking letrozole suddenly?

You should not stop taking letrozole without first speaking to your doctor. For breast cancer treatment, letrozole is usually taken long-term – for five years or longer. Stopping treatment too early can reduce its effectiveness and increase the risk of the cancer returning[1]. 

What should you do if you take too much letrozole?

If you take more letrozole than you should, contact a doctor or go to A&E straight away. Take the medication packaging with you. Symptoms of an overdose may include feeling sick, blurred vision or a fast heartbeat, and it’s important to get medical attention to minimise these effects[1]. 

What should you do if you forget a dose of letrozole?

If you forget to take your dose of letrozole, take it as soon as you remember. If it is nearly time for your next dose, skip the missed dose and take the next one at the usual time. Do not take two doses to make up for a missed one[1].  

Creating a routine of taking your dose at the same time each day can help you remember. 

What medicines should you avoid while taking letrozole?

Letrozole can interact with certain other medicines, such as tamoxifen, which can reduce the effectiveness of letrozole. Using letrozole with medicines containing oestrogen, including some hormone replacement therapies and contraceptives, should be avoided as they contain oestrogen which may prevent letrozole from working well[1]. 

Always inform your doctor or pharmacist about all medications and supplements you take before you start a new medicine, and follow the instructions in the Patient Information Leaflet[2]. 

What are the side effects of letrozole?

The most common and mild side effects of letrozole include having hot flushes, tiredness, joint or muscle pain, increased sweating, nausea and raised cholesterol[1]. 

More serious side effects include osteoporosis or bone thinning, , and liver problems (yellowing skin, dark-coloured urine, loss of appetite). If you notice these, or any unusual bleeding, signs of a blood clot, such as swelling or pain in the leg, signs of a skin disorder (rash, reddening skin or peeling, fever, blistering of lips, eyes or mouth) or have an allergic reaction to letrozole, contact your doctor immediately[1]. 

You should contact your GP if you experience any of these symptoms. In rare cases, the medicine may cause a serious allergic reaction (anaphylaxis). You should call 999 or visit A&E immediately if you believe this is happening[1]. 

If you experience any side effects, including those not listed, you are encouraged to report them via the Yellow Card Scheme or contact your doctor, pharmacist, or nurse. This information is intended as a summary for general awareness and does not replace professional medical advice. 

The information provided in the side effects section is not a comprehensive list of all possible side effects associated with this medication. For a complete list of side effects, please refer to the Patient Information Leaflet (PIL) provided with your medication or consult your healthcare professional[2]. 

Frequently asked questions about letrozole

Can I drink alcohol while taking letrozole? 

Yes, you can drink alcohol with letrozole, but you should do so in moderation. This is because alcohol can worsen some side effects such as tiredness or dizziness[1]. 

Will letrozole affect my periods? 

Letrozole may affect periods depending on your condition. For example, in postmenopausal women, periods have usually already stopped. Meanwhile, in fertility treatment, letrozole may help to regulate ovulation and stimulate a period[1]. 

Can men take letrozole? 

Men can take letrozole. It may be prescribed under specialist supervision for conditions such as male breast cancer or fertility issues[1]. 

Are there any monitoring requirements with letrozole? 

Yes, it is recommended osteoporosis risk is monitored by assessing bone mineral density before treatment and at regular intervals. Your doctor may also request other tests to safely monitor your treatment.  

What is does off-label mean? 

Off-label is a term that is used when a medicine that has a license for treating some conditions in the UK but not for the condition or specific group of patients (e.g. children) the prescribing clinician wishes to use it for[4].

For the official NHS guide to letrozole, visit their website.