Medical Oncologist
Medicines
Anastrozole vs tamoxifen: which suits you better?
Anastrozole and tamoxifen both treat hormone-receptor-positive breast cancer, but they work differently and suit different people. Anastrozole needs inactive ovaries and has a small edge after menopause; tamoxifen works at any age. This page compares how each works, their side effects, who usually takes which, and when switching between them makes sense.
NG
Medically reviewed by Dr. Naresh GunduConsultant Medical Oncologist · MBBS, DNB (Internal Medicine), DM (Medical Oncology, AIIMS) · last reviewed September 2026, next review due September 2027
On this page
- Anastrozole or tamoxifen: which suits you better?
- Four situations and the usual choice
- How the two tablets compare
- The vocabulary, in plain language
- What the comparison can and cannot show
- When switching between them makes sense
- Questions to help you and your doctor decide
- What people assume about anastrozole and tamoxifen
- Common questions about anastrozole and tamoxifen
The short answer
Anastrozole or tamoxifen: which suits you better?
Both anastrozole and tamoxifen are hormone treatments for hormone-receptor-positive breast cancer, but they work in different ways and suit different people. Anastrozole lowers the amount of oestrogen the body makes, so it only works when the ovaries are no longer active, after natural menopause or with ovarian suppression. Tamoxifen blocks oestrogen from reaching the cancer cells and works whether or not you have been through menopause. For women past menopause with early breast cancer, a large trial found that five years of anastrozole lowered the chance of the cancer returning a little more than five years of tamoxifen, which is why aromatase inhibitors such as anastrozole are often the first choice after menopause. The difference in overall survival between the two has been small. Side effects often decide the matter for an individual woman. Anastrozole more often causes joint pain and stiffness, bone thinning and a modest rise in cholesterol. Tamoxifen more often causes hot flushes and vaginal discharge, and it carries small but important risks of blood clots and cancer of the womb lining, while it tends to protect bones after menopause. Some women start on one and switch to the other, which also works well. For men with breast cancer and for women before menopause who are not having ovarian suppression, tamoxifen is usually the choice. The right tablet for you depends on your menopause status, cancer details, bone and heart health, clot risk and how you tolerate each.
Menopause status comes first
Anastrozole needs inactive ovaries; tamoxifen does not.
Anastrozole has a small edge after menopause
It lowered recurrence slightly more than tamoxifen in postmenopausal women.
Side effects often decide
Bone and joint effects on one side; clot and womb risks on the other.
This page gives general information only. Your oncologist will recommend the tablet that suits your situation.Who each suits
Four situations and the usual choice
These are general patterns; individual advice can differ.
Past menopause, healthy bones
Anastrozole or another aromatase inhibitor is often preferred for its slightly greater benefit.
Past menopause, osteoporosis or clot history
Thin bones lean away from anastrozole, while a past clot leans away from tamoxifen. Each case is weighed carefully.
Bone treatment can make anastrozole possible even with thin bones.Before menopause
Tamoxifen alone is standard. Anastrozole is only used with ovarian suppression, usually for higher-risk cancers.
Men with breast cancer
Tamoxifen is the usual first choice. An aromatase inhibitor alone is not enough in men.
Also worth knowing
- Switching partway is a recognised plan
- Both are used for DCIS in some women
- Both lower risk in some high-risk women
Side by side
How the two tablets compare
Feature
Anastrozole compared with tamoxifen
How it works
Lowers oestrogen, while tamoxifen blocks its effect on cells
Bones
Anastrozole thins bone; tamoxifen tends to protect it after menopause
Joints
Aches and stiffness are more common with anastrozole
Blood clots and womb cancer
Raised with tamoxifen, not with anastrozole
Interactions with antidepressants
Some weaken tamoxifen; anastrozole is not affected in this way
Words you will hear
The vocabulary, in plain language
- Aromatase inhibitor
- A tablet that blocks the enzyme making oestrogen after menopause, such as anastrozole.
- Selective oestrogen receptor modulator
- A medicine like tamoxifen that blocks oestrogen in breast tissue.
- Endometrium
- The lining of the womb, which tamoxifen can thicken.
- Deep vein thrombosis
- A blood clot in a leg vein, a rare but serious risk with tamoxifen.
- Switch strategy
- Taking tamoxifen for a few years, then an aromatase inhibitor, or the reverse.
- Recurrence
- Breast cancer that comes back after treatment.
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Being straight with you
What the comparison can and cannot show
Trial results describe groups of women. They cannot say exactly how either tablet would work for you.
The difference is modest
Both tablets lower the chance of recurrence substantially. The extra benefit of anastrozole after menopause is real but small.
The best tablet is the one you can keep taking
A slightly stronger medicine gives no advantage if side effects lead you to stop it early.
Indian data are limited
Most large trials were done in Western countries, although the main findings are applied widely.
What this page cannot tell you
It cannot choose between them for you. Your oncologist can, with your reports and health history.
Changing tablets
When switching between them makes sense
Starting on one tablet does not lock you in. Switching is common and is backed by research.
After two to three years of tamoxifen
Women who reach menopause during treatment are often switched to anastrozole to complete about five years.
When side effects are hard
Severe joint pain on anastrozole may lead to a trial of another aromatase inhibitor or tamoxifen. A clot on tamoxifen usually leads to a switch the other way.
Never both together
Taking anastrozole and tamoxifen at the same time worked less well than anastrozole alone, so they are only used one after the other.
At your appointment
Questions to help you and your doctor decide
A short list of questions makes the discussion clearer, especially if you are unsure about your menopause status.
About my body
Am I definitely past menopause? How healthy are my bones? Do I have a higher risk of blood clots?
About my cancer
How much difference would the choice make for my cancer, and how long will I take it?
About daily life
Which side effects are most likely for me, and what can I do if I struggle with them?
Commonly believed
What people assume about anastrozole and tamoxifen
Tamoxifen is old, so it must be inferior.
Tamoxifen remains an effective, widely used treatment, and the best choice for many people.
Taking both would give double protection.
The combination worked less well than anastrozole alone.
Anastrozole works for everyone with hormone-positive cancer.
It needs inactive ovaries, so it does not work alone before menopause.
Switching tablets means treatment has failed.
Switching is a planned, proven approach and often helps with side effects.
Questions we are asked
Common questions about anastrozole and tamoxifen
Is anastrozole stronger than tamoxifen?
After menopause, anastrozole lowered the chance of recurrence slightly more in trials. Stronger is not quite the right word, though. Both work well, and the better choice depends on your menopause status, other health conditions and which side effects you can live with.
Why was I given tamoxifen instead?
Common reasons include still having periods, uncertain menopause after chemotherapy, thin bones, severe arthritis or a lower-risk cancer. Tamoxifen is an excellent treatment. Ask your oncologist to explain the reasons in your case.
Can I change from tamoxifen to anastrozole later?
Often, yes, once menopause is confirmed. Many women take tamoxifen for two to three years and then switch to complete about five years of treatment. Your doctor may check hormone levels first if your periods stopped because of chemotherapy.
Which has fewer side effects?
Neither is free of them, and they differ in type rather than amount. Anastrozole brings more joint and bone problems. Tamoxifen brings more hot flushes, discharge, and small risks of clots and womb cancer. How each affects you personally can only be learnt by trying.
Does tamoxifen protect my bones?
After menopause, tamoxifen tends to help keep bones stronger. Before menopause it can cause slight bone loss. Anastrozole thins bones in most women, so bone checks and often vitamin D and calcium are advised while you take it.
Do I need womb checks on either tablet?
Routine womb scans are not usually needed on either. On tamoxifen, report any vaginal bleeding after menopause straight away, as it needs checking. Anastrozole does not raise the risk of womb cancer, but unusual bleeding should still be reported.
Can men take anastrozole?
In men, the testes keep making hormones that can be turned into oestrogen, so an aromatase inhibitor alone is not enough. Tamoxifen is usually the first choice. Anastrozole may occasionally be used together with a medicine that lowers testosterone.
Is there a survival difference between them?
In large trials after menopause, anastrozole reduced recurrence a little more, but the difference in overall survival was small and not clearly shown. Taking whichever tablet you are prescribed steadily, for the full course, matters more than which one it is.
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Sources
- National Cancer Institute — Hormone therapy for breast cancer
- American Cancer Society — Hormone therapy for breast cancer
- Breast Cancer Now — Anastrozole (Arimidex)
This page is general information, not a prescription. Do not change or stop any treatment based on what you read here. If anything is worrying you, contact your own treating team — or call our helpline and we will help you reach the right specialist.