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Hormone therapy

Is Letrozole or Anastrozole — a Type of Chemotherapy?

Letrozole and anastrozole are often called chemo tablets, but they are not chemotherapy. They work by a completely different mechanism, cause different side effects, and need entirely different self-care. Knowing which type of medicine you are on changes the advice you should follow.

Medically reviewed by Dr. Naresh Gundu, Medical Oncologist, MBBS (Chalmeda Anand Rao Institute of Medical Sciences, Karimnagar) · DNB Internal Medicine (Sir Gangaram Hospital, New Delhi) · DM Medical Oncology (AIIMS) · Last reviewed September 2026

  • Not chemotherapy — They lower oestrogen levels rather than killing dividing cells. The guidance written for chemotherapy patients does not apply to you.
  • Different side effects — Joint pain and bone thinning are common. Significant hair loss and severe nausea are not.
  • Taken daily as a tablet — This is a long-term oral medicine, usually continued for several years without breaks.
  • Tell your team everything you take — Some herbal and traditional medicines interact with hormone therapy. Your team needs to know.
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Letrozole and anastrozole are not chemotherapy. They are aromatase inhibitors — a type of hormone therapy that lowers oestrogen levels. Because they work differently from chemotherapy, they cause different side effects: joint stiffness and bone thinning are common; hair loss and nausea are not. Advice meant for chemotherapy patients does not apply to you.

What do these words mean?

Aromatase inhibitor
The class of drug that letrozole and anastrozole belong to. They block an enzyme called aromatase, which the body uses to produce oestrogen after menopause. Less oestrogen means less fuel for hormone-sensitive cancer cells.
Hormone receptor-positive (HR+)
A description of breast cancers whose cells carry receptors that respond to oestrogen or progesterone. Your pathology report will say ER-positive, PR-positive or HR-positive. Aromatase inhibitors are prescribed specifically for this type.
Chemotherapy
A separate class of treatment using drugs that attack fast-dividing cells across the body. Letrozole and anastrozole do not work this way, which is why classic chemotherapy effects — significant hair loss, severe nausea, a suppressed immune system — are not part of their profile.
Aromatase
An enzyme found mainly in fat tissue that converts other hormones into oestrogen. After menopause, this is how the body makes most of its oestrogen. Aromatase inhibitors block that conversion, which is how they work.

What do I need to know if I am taking letrozole or anastrozole?

  • Significant hair loss is not an expected side effect — you do not need to plan for a wig.
  • Severe nausea is not expected — you do not need routine anti-nausea medicine.
  • Your immune system is not suppressed. You do not need to avoid crowds or sick contacts because of this medicine.
  • Joint stiffness and aches are common and worth reporting to your team — they can often be helped.
  • Your bone density needs monitoring. Your team may arrange a DEXA scan.
  • This tablet works when taken every day, usually for several years. Do not stop without talking to your team.
  • Tell your team about any herbal, Ayurvedic or traditional medicines you are taking alongside it.

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What side effects does letrozole actually cause?

Joint pain and stiffness — sometimes called arthralgia — is the most commonly reported side effect. It often affects the hands, knees and wrists, and may be worse in the morning.

Bone thinning is a longer-term concern because oestrogen normally helps maintain bone density. Your team may measure your bone density with a DEXA scan and may recommend calcium, vitamin D or other medicines to protect your bones.

Hot flushes, night sweats and disrupted sleep are common. They happen because oestrogen levels fall significantly.

Fatigue is reported by many people on aromatase inhibitors. It is generally milder than the exhaustion associated with chemotherapy and does not follow the same cycle pattern.

Why does it matter whether it is called chemotherapy?

Chemotherapy guidance — eat soft foods for nausea, stay home from crowds, watch for infection, expect hair to fall — is built around effects that aromatase inhibitors do not cause.

Following chemotherapy advice when you are on hormone therapy can make you more anxious than you need to be. It can also lead you to stop your tablet when you feel discomfort, when in fact it needs to be taken consistently over years to work.

If you are unsure whether advice you have read applies to your specific medicine, ask your oncologist. Bring the source with you — your team would rather answer that question than have you follow guidance written for a different treatment.

Did you know?

Joint pain is one of the most commonly cited reasons people stop aromatase inhibitors early, according to ASCO guidance on hormone therapy adherence.

Stopping early reduces the protection the medicine is intended to provide. If joint pain is affecting your daily life, tell your team before you stop — switching from one aromatase inhibitor to the other sometimes reduces the effect.

Source: ASCO Clinical Practice Guidance: Adjuvant Endocrine Therapy for Hormone Receptor–Positive Breast Cancer

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Common questions

Frequently asked questions

Does letrozole cause hair loss?

Letrozole does not cause the hair loss pattern associated with chemotherapy. Some people notice mild thinning after long-term use, but significant hair loss — the kind that requires a wig or causes visible patches — is not a recognised effect of aromatase inhibitors. If you are noticing noticeable thinning, mention it to your team, as there can be other causes worth investigating.

Will I feel sick or nauseous on letrozole?

Severe nausea is not a major expected side effect of letrozole or anastrozole, and you do not need routine anti-nausea medicines. If you are feeling persistently nauseous after starting your tablet, let your team know — it is worth checking rather than assuming it is an expected part of treatment.

What is the difference between letrozole and anastrozole?

Both are aromatase inhibitors that work in the same way. The difference lies in their chemical structure. Your oncologist chose one based on factors specific to your situation, which may include how your body tolerates it and other medicines you take. If joint pain or another side effect is difficult on one, it is reasonable to ask your team whether switching to the other might help.

Do I need to avoid sick people while I am on letrozole?

No. Letrozole and anastrozole do not suppress your immune system the way chemotherapy does. You do not need to avoid crowds, public transport or sick contacts because of this medicine. Standard hygiene — handwashing and sensible caution when someone at home is unwell — is enough. This is one of the important differences from chemotherapy.

Will letrozole or anastrozole affect my bones?

Yes, and your team should already be thinking about this. Oestrogen helps protect bone density, and aromatase inhibitors reduce oestrogen levels significantly over time. Long-term use can lead to bone thinning. Your team may arrange a DEXA scan to measure your baseline bone density and repeat it during treatment. They may also recommend calcium, vitamin D or other medicines. Tell your team about any back pain, or if you have a fall at home.

Can I stop taking letrozole if the side effects are too hard?

Not without speaking to your team first. Stopping early reduces the protection the medicine is intended to provide. If side effects — particularly joint pain or fatigue — are affecting your daily life, there are options your team can offer before stopping is considered. These include adjusting when in the day you take it, switching to the other aromatase inhibitor, or medicines that help with joint pain. Bring it up at your next appointment, or call before then if it is affecting you now.

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