Letrozole: What it treats and what you need to know

Letrozole is an oral aromatase inhibitor that shows up a lot in breast cancer care and fertility treatment. It lowers estrogen production, which helps stop certain breast cancers from growing and can trigger ovulation for people trying to conceive. Knowing the usual doses, possible side effects, and safety checks helps you use it smarter and safer.

How Letrozole works

Letrozole blocks an enzyme called aromatase so the body makes less estrogen. In postmenopausal women with estrogen-receptor positive breast cancer, that lower estrogen slows cancer growth and lowers recurrence risk. For fertility, short courses of letrozole reduce estrogen briefly, which can boost follicle-stimulating hormone release and help an egg mature. The goal and timing change depending on whether it’s used for cancer or to help ovulate.

Typical doses and timing

For early or advanced breast cancer, the common dose is 2.5 mg once daily, often for several years as your doctor recommends. For ovulation induction, doctors usually prescribe 2.5–5 mg daily for five days early in the menstrual cycle, often starting on cycle day 3, 4, or 5. Never change dose or stop suddenly without talking to your prescriber—timing matters for both safety and effectiveness.

Side effects and what to watch for

Common side effects are hot flashes, joint and muscle pain, fatigue, and mood changes. Letrozole can reduce bone density over time, so your doctor may check bone health with a DEXA scan and suggest calcium, vitamin D, or other treatments. Serious but less common issues include liver enzyme changes or unexpected heavy symptoms—report any unusual aches, persistent fatigue, or new symptoms right away.

Interactions, precautions, and pregnancy risk

Letrozole interacts with strong enzyme inducers or inhibitors that change its blood levels. Tell your clinician about all medicines, supplements, and herbal products you take. It can cause severe harm to a fetus, so it must never be used during pregnancy. If you’re using it for fertility, your doctor will explain timing, pregnancy testing, and when it’s safe to stop.

Monitoring and safe use

Your care team will tailor monitoring: bone density checks, symptom reviews, and routine blood work when needed. If you buy medicines online, use only licensed pharmacies that ask for a prescription and show clear contact details. Ask questions: why this dose, how long, and what to expect day-to-day. That makes side effects easier to manage and keeps treatment on track.

If you have specific concerns—planning pregnancy, a history of bone loss, liver disease, or multiple medications—bring them up with your provider early. Letrozole can be very effective, but it works best when you and your clinician plan treatment and follow-up together.