Letrozole

Say it: LET-roh-zole · Brand names: Femara

Letrozole is a hormone therapy pill called an aromatase inhibitor that lowers the amount of estrogen in the body.

What it is

After menopause, the body still makes some estrogen using an enzyme called aromatase. Letrozole blocks this enzyme so the body makes much less estrogen. Breast cancers that need estrogen to grow then slow down or stop.

Often used for

• hormone receptor positive early breast cancer after menopause, to lower the chance it comes back
• hormone receptor positive breast cancer after menopause that is advanced or has spread

How you get it

Letrozole is a pill you take by mouth at home, once a day, with or without food. It is often taken for 5 years or longer. Your schedule may be different.

Common side effects and what helps

• Hot flashes or night sweats. Dress in layers, keep your room cool, and limit caffeine and alcohol.
• Joint or muscle aches and stiffness. Regular gentle exercise often helps.
• Feeling tired or weak. Rest when you need to, and try short walks.
• Feeling dizzy. Stand up slowly and be careful when driving.
• Thinning bones. Ask your team about calcium, vitamin D, and exercise.
• Higher cholesterol. You may have blood tests to check.
• Headache. Ask your team which pain medicines are safe.
• Swelling in your hands or feet. Raise your legs when you sit.

Call your care team right away if you have

• Chest pain or pressure, or a racing or pounding heartbeat
• Sudden weakness or numbness of the face, arm, or leg, or trouble speaking
• Swelling, pain, or warmth in one leg, or sudden shortness of breath
• Bone pain that is new or very bad, or a broken bone

Before you start, tell your team

• If you are pregnant, may become pregnant, or are breastfeeding
• If you have not gone through menopause
• If you have bone thinning (osteoporosis)
• If you have liver problems or high cholesterol
• If you take any medicine or supplement with estrogen, since it can stop this medicine from working

Good to know

• It can thin your bones over time. You may have bone density scans, and your team may suggest calcium, vitamin D, or other medicines.
• Your cholesterol may be checked.
• It can cause tiredness and dizziness. Be careful driving until you know how it affects you.

At home

• Take the tablet at about the same time each day.
• If you miss a dose or throw up after taking it, ask your team what to do. Do not take extra pills to make up for it.
• Store the pills at room temperature in the original bottle, away from children and pets.

Questions to ask

• How long will I take this medicine?
• Do I need a bone density scan?
• What can I do about joint aches?
• What can I do about hot flashes?

Side effect guides

• Fatigue (tiredness)
• Pain

Last updated: 2026-10-27. Medically reviewed by Veli Bakalov, MD, medical oncologist (October 2026). General education from Step by Step, the patient portal of HemeOncBuddy.