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Drug Formulary

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letrozole

( LETT-row-zole )

Other Name(s): Femara®

Appearance: tablet

letrozole patient.pdf

ltrozole pour le patient.pdf

letrozole

Pronunciation:

LETT-row-zole

Other Name(s):

Femara®

Appearance:

tablet

This handout gives general information about this cancer medication.

You will learn:

who to contact for help
what the medication is
how it is given
what to expect while on medication

This handout was created by Ontario Health (Cancer Care Ontario) together with patients and their caregivers who have also gone through cancer treatment. It is meant to help support you through your cancer treatment and answer some of your questions.

This information does not replace the advice of your health care team. Always talk to your health care team about your treatment.

Who do I contact if I have questions or need help?

My cancer health care provider is: _____________________________________________

During the day I should contact: _______________________________________________

Evenings, weekends and holidays: _____________________________________________

This page gives general information about this cancer medication.

You will learn:

who to contact for help
what the medication is
how it is given
what to expect while on this medication

This information was created by Ontario Health (Cancer Care Ontario) together with patients and their caregivers who have also gone through cancer treatment. It is meant to help support you through your cancer treatment and answer some of your questions.

This information does not replace the advice of your health care team. Always talk to your health care team about your treatment.

What is this treatment for?

For treating a certain type of hormone sensitive breast cancer, and other cancers

What should I do before I start this treatment?

Tell your health care team if you have or had significant medical condition(s), especially if you have / had:

liver, kidney or heart problems,
uncontrolled blood pressure,
high cholesterol levels,
muscle or joint pain,
bone thinning / loss or bone fractures (or if you have family members that have / had either of these), or
any allergies.

Letrozole tablets may contain a small amount of lactose. If you cannot tolerate lactose, talk to your health care team.

Remember To:

Tell your health care team about all of the other medications you are taking.
Keep taking other medications that have been prescribed for you, unless you have been told not to by your health care team.

How is this treatment given?

This medication is usually taken once a day by mouth. Talk to your health care team about how and when to take your medication.
Swallow whole with a glass of water, with or without food.
Do not crush or chew tablets.
If you miss a dose, take it as soon as you can remember. If it is close to your next dose (for example, within 2 to 3 hours), skip it and take your next dose as scheduled. Do not take an extra dose to make up for the missed dose.
If you vomit (throw up) after taking your medication, talk to your health care team about what to do.

Warning: If you take too much of this medication by accident, or if you think a child or a pet may have swallowed your medication, you must call the Ontario Poison Control Center right away at: 1-800-268-9017.

DO this while on treatment

DO check with your health care team before getting any vaccinations, surgery, dental work or other medical procedures.
DO talk to your health care team about your risk of getting osteoporosis or heart problems after this treatment.

DO NOT do this while on treatment

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DO NOT take any other medications, such as vitamins, over-the-counter (non-prescription) drugs or substances, or natural health products without checking with your health care team.

DO NOT start any complementary or alternative therapies, such as acupuncture or homeopathic products, without checking with your health care team.

DO NOT use tobacco products (such as smoking cigarettes or vaping) or drink alcohol while on treatment without talking to your health care team first. Smoking and drinking can make side effects worse and make your treatment not work as well.
DO NOT drive, operate machinery or do any tasks that need you to be alert if you feel fatigued, dizzy, or drowsy (less common).

DO this while on treatment

Check Mark Icon

DO check with your health care team before getting any vaccinations, surgery, dental work or other medical procedures.
DO talk to your health care team about your risk of getting osteoporosis or heart problems after this treatment.

DO NOT do this while on treatment

Stop Icon

DO NOT take any other medications, such as vitamins, over-the-counter (non-prescription) drugs or substances, or natural health products without checking with your health care team.

DO NOT start any complementary or alternative therapies, such as acupuncture or homeopathic products, without checking with your health care team.

DO NOT use tobacco products (such as smoking cigarettes or vaping) or drink alcohol while on treatment without talking to your health care team first. Smoking and drinking can make side effects worse and make your treatment not work as well.
DO NOT drive, operate machinery or do any tasks that need you to be alert if you feel fatigued, dizzy, or drowsy (less common).

Will this treatment interact with other medications or natural health products?

Yes, this medication can interact with other medications, vitamins, foods, traditional medicines and natural health products. Interactions can make this medication not work as well or cause severe side effects.

Tell your health care team about all of your:

prescription and over-the-counter (non-prescription) medications
other drugs and substances, such as cannabis/marijuana (medical or recreational)
natural health products such as vitamins, herbal teas, homeopathic medicines, and other supplements, or traditional medicines

Check with your health care team before starting or stopping any of them.

Do not take any treatment containing estrogen (including herbal supplements) while you are on letrozole, as this can make your treatment not work as well.

Talk to your health care team BEFORE taking or using these :

Anti-inflammatory medications such as ibuprofen (Advil^® or Motrin^®), naproxen (Aleve^®) or Aspirin^®.
Over-the-counter products such as dimenhydrinate (Gravol^®)
Natural health products such as St. John’s Wort
Traditional medicines
Supplements such as vitamin C
Grapefruit juice
Alcoholic drinks
Tobacco
All other drugs or substances, such as marijuana or cannabis (medical or recreational)

How will this treatment affect sex, pregnancy and breastfeeding?

Talk to your health care team about:

How this medication may affect your sexual health.
How this medication may affect your ability to have a baby, if this applies to you.

This treatment may harm an unborn baby. Tell your health care team if you or your partner are pregnant, become pregnant during treatment, or are breastfeeding.

If there is any chance you may become pregnant, you and your partner together must use 2 effective forms of birth control at the same time until at least 20 days after your last dose. Talk to your health care team about which birth control options are best for you.
If you are a patient that can get somebody pregnant, you and your partner together must use 2 effective forms of birth control at the same time until at least 6 months (general recommendation) after your last dose. Talk to your health care team about which birth control options are best for you.
Do not breastfeed while on this treatment.

How to safely store and handle this medication

Do not throw out any unused medications at home. Bring them to your pharmacy to be thrown away safely.

Keep this medication in the original packaging at room temperature in a dry place, away from heat and light. Keep out of sight and reach of children and pets.

How to safely touch oral anti-cancer medication

If you are a patient:

Wash your hands before and after touching your oral anti-cancer medication.
Swallow each pill whole. Do not crush or chew your pills.

If you are a caregiver:

Wash your hands before and after touching the oral anti-cancer medication.

If you are pregnant or breastfeeding, or if there is a chance you or your partner may become pregnant:

Wear nitrile or latex gloves when touching tablets, capsules or liquids.
Wash your hands before putting on your gloves and after taking them off, even if your skin did not touch the oral anti-cancer medication.
Throw out your gloves after each use. Do not re-use gloves.

What to do if anti-cancer medication gets on your skin or in your eyes

If medication gets on your skin:

Wash your skin with a lot of soap and water. .
If your skin gets red or irritated, talk to your health care team.

If medication gets in your eyes:

Rinse your eyes with running water right away. Keep water flowing over your open eyes for at least 15 minutes.

What are the side effects of this treatment?

The following table lists side effects that you may have when getting letrozole. The table is set up to list the most common side effects first and the least common last. It is unlikely that you will have all of the side effects listed and you may have some that are not listed.

Read over the side effect table so that you know what to look for and when to get help. Refer to this table if you experience any side effects while on letrozole.

Very Common Side Effects (50 or more out of 100 people)
Changes to your hormone levels Your treatment causes changes in the levels of estrogen in your body. This can affect your mood, energy levels or physical appearance, among other things. You may have many of these symptoms or none at all. Your symptoms may also change at different times in your treatment. What to look for? Hot flashes: A hot flash feels like a sudden warmth in your upper body and face. It can happen quickly and with no warning. Your face may get flushed (turn red) and you may sweat more. Hot flashes can cause you to have trouble sleeping. Other symptoms of having low estrogen levels: Vaginal dryness (possibly with discharge or bleeding) Memory loss Mood changes, depression Thinning of the bones and increased risk of fracture What to do? To help prevent hot flashes: Avoid triggers such as spicy food, alcohol and caffeine (tea, coffee, and soft drinks). Exercise regularly. Ask your health care team what exercises are appropriate for you before you start any new exercise. Quitting smoking may also help. If you have hot flashes: To keep cool, dress in light, cotton clothing or in layers that you can easily remove. Use a fan. Drink plenty of water or other liquids (at least 6 to 8 cups) unless your health care team has told you to drink more or less. Lay a towel on top of your bed sheet before you sleep so you can change it easily if you sweat at night. Hot flashes may improve over time. Talk to your health care team if this or any symptoms of low estrogen are bothersome for you.	Talk to your health care team if it does not improve or if it is severe.

Very Common Side Effects (50 or more out of 100 people)

Side effects and what to do

When to contact health care team

Changes to your hormone levels

Your treatment causes changes in the levels of estrogen in your body. This can affect your mood, energy levels or physical appearance, among other things.

You may have many of these symptoms or none at all. Your symptoms may also change at different times in your treatment.

What to look for?

Hot flashes:

A hot flash feels like a sudden warmth in your upper body and face. It can happen quickly and with no warning.
Your face may get flushed (turn red) and you may sweat more.
Hot flashes can cause you to have trouble sleeping.

Other symptoms of having low estrogen levels:

Vaginal dryness (possibly with discharge or bleeding)
Memory loss
Mood changes, depression
Thinning of the bones and increased risk of fracture

What to do?

To help prevent hot flashes:

Avoid triggers such as spicy food, alcohol and caffeine (tea, coffee, and soft drinks).
Exercise regularly. Ask your health care team what exercises are appropriate for you before you start any new exercise.
Quitting smoking may also help.

If you have hot flashes:

To keep cool, dress in light, cotton clothing or in layers that you can easily remove. Use a fan.
Drink plenty of water or other liquids (at least 6 to 8 cups) unless your health care team has told you to drink more or less.
Lay a towel on top of your bed sheet before you sleep so you can change it easily if you sweat at night.

Hot flashes may improve over time. Talk to your health care team if this or any symptoms of low estrogen are bothersome for you.

Talk to your health care team if it does not improve or if it is severe.

Common Side Effects (25 to 49 out of 100 people)
Side effects and what to do	When to contact health care team
Fatigue What to look for? Feeling of tiredness or low energy that lasts a long time and does not go away with rest or sleep. What to do? Be active. Aim to get 30 minutes of moderate exercise (you are able to talk comfortably while exercising) on most days. Check with your health care team before starting any new exercise. Pace yourself, do not rush. Put off less important activities. Rest when you need to. Ask family or friends to help you with things like housework, shopping, and child or pet care. Eat well and drink at least 6 to 8 glasses of water or other liquids every day (unless your health care team has told you to drink more or less). Avoid driving or using machinery if you are feeling tired. Ask your health care team for the Fatigue pamphlet for more information.	Talk to your health care team if it does not improve or if it is severe.
Headache; Mild joint, muscle pain or cramps What to look for? A mild headache New pain in your muscles or joints, muscle cramps, or feeling achy. What to do? Take pain medication (acetaminophen or opioids such as codeine, morphine, hydromorphone, oxycodone) as prescribed. Rest often and try light exercise (such as walking) as it may help. Ask your health care team for the Pain pamphlet for more information.	Talk to your health care team if it does not improve or if it is severe.
Mild swelling What to look for? You may have mild swelling or puffiness in your arms and/or legs. Rarely, this may be severe. What to do? To help prevent swelling: Eat a low-salt diet. If you have swelling: Wear loose-fitting clothing. For swollen legs or feet, keep your feet up when sitting.	Talk to your health care team if it does not improve or if it is severe.

Less Common Side Effects (10 to 24 out of 100 people)
Side effects and what to do	When to contact health care team
Higher than normal cholesterol or fat levels in the blood What to look for? High cholesterol or fat levels usually do not cause any symptoms. Since your treatment may cause high cholesterol, your health care team may do regular blood tests to check your cholesterol levels. What to do? Your health care team may give you medication to treat high cholesterol or fat levels. If you already take medication for high cholesterol or fat levels, your health care team may change the amount or type of medication you take.	Talk to your health care team if it does not improve or if it is severe.
Dizziness What to look for? You may feel light-headed and like you might faint (pass out). What to do? Lay down right away so you do not fall. Slowly get up and start moving once you feel better. Do not drive a motor vehicle or use machinery if you feel dizzy.	Talk to your health care team if it does not improve or if it is severe.
Constipation What to look for? Having bowel movements (going poo) less often than normal. Small hard stools (poo) that look like pellets. The need to push hard and strain to have any stool (poo) come out. Stomach ache or cramps. A bloated belly, feeling of fullness, or discomfort. Leaking of watery stools (poo). Lots of gas or burping. Nausea or vomiting. What to do? To help prevent constipation: Try to eat more fiber rich foods like fruits with skin, leafy greens and whole grains. Drink at least 6 to 8 cups of liquids each day unless your health care team has told you to drink more or less. Be Active. Exercise can help to keep you regular. If you take opioid pain medication, ask your health care team if eating more fibre is right for you. To help treat constipation: If you have not had a bowel movement in 2 to 3 days you may need to take a laxative (medication to help you poo) to help you have regular bowel movements. Ask your health care team what to do. Ask your health care team for the Constipation Pamphlet for more information.	Talk to your health care team if it does not improve or if it is severe.
Nausea and vomiting (generally mild) What to look for? Nausea is feeling like you need to throw up. You may also feel light-headed. You may feel nausea within hours to days after your treatment. What to do? To help prevent nausea: It is easier to prevent nausea than to treat it once it happens. Drink clear liquids and have small meals. Get fresh air and rest. Do not eat spicy, fried foods or foods with a strong smell. Limit caffeine (like coffee, tea) and avoid alcohol. If you have nausea or vomiting: Take your rescue (as-needed) anti-nausea medication(s) as prescribed. Ask your health care team for the Nausea & Vomiting pamphlet for more information. Talk to your health care team if: nausea lasts more than 48 hours vomiting lasts more than 24 hours or if it is severe	Talk to your healthcare team if nausea lasts more than 48 hours or vomiting lasts more than 24 hours or if it is severe.
Bone pain; Bone loss or Bone fractures Your treatment may cause your bones to thin earlier than normal. Thin bones are weak and fragile. They may break easily from simple falls or movements. Your health care team may check your bone density (measure of how strong your bones are) with a bone scan. What to look for? You may have severe or unusual bone pain especially in your back, hips and wrist. What to do? To help prevent bone loss and fractures Your health care team may ask you to change your diet, or may ask you to take calcium and vitamin D supplements, or other prescription medications. Talk to your health care team before taking any supplements. Get emergency medical help if you experience severe bone pain or are unable to move as these may be signs of a bone fracture. See our Bone Health During Cancer Treatment pamphlet for more information.	Talk to your health care team if it does not improve. Get emergency medical help If you have severe bone pain or are unable to move.

Other rare, but serious side effects are possible with this treatment.

If you have any of the following, talk to your cancer health care team or get emergency medical help right away:

pain, swelling or hardening of vein in your arms or legs
sudden start of coughing, problems breathing, pain in your chest or coughing blood
trouble seeing, speaking, or using your arms and legs
severe rash (may blister or peel), swollen face, lips or tongue, chest or throat tightness
blurred, cloudy or dim vision, difficulty seeing at night
irregular heartbeat, chest pain, fainting, swelling in legs/ankles/belly, shortness of breath

For more information on how to manage your symptoms ask your health care provider, or visit: https://www.cancercareontario.ca/symptoms.

Notes

August 2025 Updated/revised information sheet

The information set out in the medication information sheets, regimen information sheets, and symptom management information (for patients) contained in the Drug Formulary (the "Formulary") is intended to be used by health professionals and patients for informational purposes only. The information is not intended to cover all possible uses, directions, precautions, drug interactions or side effects of a certain drug, nor should it be used to indicate that use of a particular drug is safe, appropriate or effective for a given condition.

A patient should always consult a healthcare provider if he/she has any questions regarding the information set out in the Formulary. The information in the Formulary is not intended to act as or replace medical advice and should not be relied upon in any such regard. All uses of the Formulary are subject to clinical judgment and actual prescribing patterns may not follow the information provided in the Formulary.

letrozole

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Symptom Management

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