Letrozole: what it does and what to watch
Also known as: Aromatase inhibitor, Hormone therapy · Hormone therapy (aromatase inhibitor) · Updated 2026-08-20 · Educational — not medical advice
In plain language: This medicine blocks the aromatase enzyme responsible for the final step in converting other hormones into estrogen in body tissues outside the ovaries, sharply lowering estrogen levels in the body. Because many breast cancer cells depend on estrogen to grow, reducing its availability can slow or stop tumor growth.
What it's used for
- Treatment of hormone-receptor-positive breast cancer, mainly in postmenopausal women
- Reducing the risk of breast cancer recurrence after primary treatment
- Sometimes used to stimulate ovulation for fertility purposes
Common side effects
- Hot flushes
- Joint and muscle aches
- Fatigue
- Night sweats
- Mild nausea
Get medical help if…
Bone thinning and increased fracture risk with long-term use
Rise in cholesterol levels
Rare heart-related effects, more relevant in people with existing heart disease
Lab values it can move
Few guides tell you this part: medicines show up in blood work. If you take Letrozole and a value below looks off on your report, this may be part of the story — never stop a medicine without your doctor.
This medicine's effect on lowering estrogen can raise LDL cholesterol over time, so lipid levels are sometimes checked periodically.
LDL CholesterolOverall cholesterol may rise during treatment, related to the drop in estrogen, and is monitored as part of routine care.
Total CholesterolGood to know
- Bone density scans are often recommended before and periodically during treatment, since estrogen normally helps protect bone strength
- Joint aches are common and usually manageable, but persistent or severe pain should be discussed with a prescriber
- Cholesterol levels may be checked periodically during treatment
- Calcium and vitamin D intake, along with weight-bearing activity, are often encouraged to support bone health
- This medicine is usually taken for several years as advised by an oncology team
Questions people ask
Why does this medicine affect my bones?
Estrogen normally helps maintain bone density, and this medicine works by sharply lowering estrogen levels throughout the body. Over time, this can lead to bone thinning and a higher risk of fractures. Bone density scans, along with adequate calcium, vitamin D, and weight-bearing exercise, are commonly recommended to help protect bone health during treatment.
Will the joint aches from this medicine ever go away?
Joint and muscle aches are a common effect of lowering estrogen and often ease somewhat over the first months of treatment, though they can persist for some people. They are usually manageable with simple measures, but severe or worsening joint pain should be discussed with a prescriber, since dose timing or supportive measures can sometimes help.
Taking Letrozole? See what your blood work says.
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