Medical Oncologist
Hormone therapy
Tamoxifen or an aromatase inhibitor: how the choice is made
The choice between tamoxifen and an aromatase inhibitor depends mainly on menopause. Aromatase inhibitors work after menopause or with ovarian suppression; tamoxifen works before and after. Bone health, clot risk and side effects also count. This page explains, in general terms, how the decision is made.
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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
- How do oncologists choose between tamoxifen and an aromatase inhibitor?
- Tamoxifen and aromatase inhibitors, in general terms
- The factors your oncologist considers
- The vocabulary, in plain language
- What the difference really amounts to
- Managing the common side effects of each
- Choices for women who have not reached menopause
- Practical points for taking hormone tablets for years
- What people assume about tamoxifen and aromatase inhibitors
- Common questions about choosing a hormone tablet
The short answer
How do oncologists choose between tamoxifen and an aromatase inhibitor?
The main deciding factor is whether you have been through menopause. Aromatase inhibitors, such as letrozole, anastrozole and exemestane, only work when the ovaries are no longer making oestrogen, so they are used after menopause or together with ovarian suppression before it. Tamoxifen works both before and after menopause. After menopause, aromatase inhibitors lower the chance of recurrence a little more than tamoxifen for most women, but side effects and other health conditions also shape the choice.
How the two work differently
Tamoxifen blocks oestrogen from attaching to cancer cells. Aromatase inhibitors lower the amount of oestrogen the body makes after menopause, by blocking an enzyme in fat and other tissues. Both starve hormone-sensitive cancer cells of the signal they use to grow.
What else is weighed
Bone health, the risk of blood clots, womb health, joint problems, your cancer's risk level and your own experience of side effects all feed into the choice. Many women switch between the two at some point.
When the usual choice is set aside
A history of blood clots may steer away from tamoxifen. Severe osteoporosis or disabling joint pain may steer away from an aromatase inhibitor. In these situations the other option is usually still effective.
This page gives general information only. Which tablet suits you is a decision for your oncologist.Side by side
Tamoxifen and aromatase inhibitors, in general terms
Tamoxifen
Aromatase inhibitors
Works before and after menopause
After menopause, or with ovarian suppression
Blocks oestrogen at the cancer cell
Lowers oestrogen levels in the body
Small risk of blood clots and womb changes
Joint pain and bone thinning more common
Tends to protect bones after menopause
Bone density scans usually needed
Hot flushes common
Hot flushes and vaginal dryness common
What decides it
The factors your oncologist considers
Menopausal status comes first, but several other factors can change the choice.
Menopausal status
Whether your periods have stopped naturally, stopped with chemotherapy, or are expected to return. Chemotherapy can stop periods without permanently ending ovarian function.
Your cancer's risk
For higher-risk cancers in younger women, an aromatase inhibitor with ovarian suppression may be preferred over tamoxifen alone.
Blood tests may confirm menopause.Bones and joints
Existing osteoporosis or severe arthritis can make an aromatase inhibitor harder to take.
Clots and womb health
A past clot, stroke, or certain womb conditions can make tamoxifen less suitable.
Tell your oncologist about
- Any past blood clots
- Bone density problems
- Other medicines you take
Words you will hear
The vocabulary, in plain language
- Tamoxifen
- A hormone tablet that blocks oestrogen from reaching cancer cells.
- Aromatase inhibitor
- A hormone tablet that lowers oestrogen made after menopause.
- Letrozole, anastrozole, exemestane
- The three aromatase inhibitors commonly used.
- Ovarian suppression
- Injections or surgery that stop the ovaries making oestrogen.
- Postmenopausal
- After the ovaries have permanently stopped producing oestrogen.
- Sequential therapy
- Taking one tablet for a few years and then switching to the other.
Being straight with you
What the difference really amounts to
After menopause, aromatase inhibitors lower the chance of recurrence a little more than tamoxifen in large studies. The difference is real but modest, and both tablets are effective. The better tablet for you is the one that suits your body and that you can keep taking for years.
Taking it consistently matters more than the choice
A tablet taken regularly for the planned years does far more good than a slightly stronger tablet abandoned after a year because of side effects. If side effects are hard, a switch is usually better than stopping.
Menopause after chemotherapy is tricky
Periods that stop during chemotherapy can return, sometimes a year or more later. Starting an aromatase inhibitor without confirming menopause can allow the ovaries to restart, which is why blood tests or ovarian suppression are often used.
Both carry long-term effects
Tamoxifen brings a small risk of clots and womb changes. Aromatase inhibitors bring bone thinning and joint pain. Neither is free of trade-offs.
What this page cannot tell you
It cannot tell you which tablet suits you. Ask your oncologist why they recommend the one they do.
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Side effects
Managing the common side effects of each
Most women have some side effects on hormone therapy. Knowing what to expect, and what helps, makes the years of treatment more manageable.
On tamoxifen
Hot flushes are the most common complaint. Report any unusual vaginal bleeding, especially after menopause, because tamoxifen can thicken the womb lining. Leg swelling, pain or sudden breathlessness need urgent attention because of the small risk of clots.
On an aromatase inhibitor
Joint stiffness and aching, particularly in the hands and knees, are common. Regular exercise, weight management and simple pain relief help many women. Bone density scans, calcium and vitamin D, and sometimes bone medicines, protect the skeleton.
On either
Mood changes, tiredness, vaginal dryness and low libido can occur. They are treatable, so mention them rather than assuming they must be endured.
Before menopause
Choices for women who have not reached menopause
For premenopausal women, the options depend largely on the risk level of the cancer.
Tamoxifen alone
For many lower-risk cancers, tamoxifen alone for several years is an effective choice that keeps the ovaries working.
Ovarian suppression added
For higher-risk cancers, especially in younger women, adding injections that switch off the ovaries, with either tamoxifen or an aromatase inhibitor, lowers the chance of recurrence further. It brings stronger menopause-like symptoms, which your team can help manage.
Thinking about fertility
Pregnancy is not safe on hormone therapy. If you hope to have children, discuss timing, fertility preservation and the possibility of a planned break with your oncologist early.
Day to day
Practical points for taking hormone tablets for years
Whichever tablet you take, the practical side of daily treatment over many years makes a real difference to how well it works.
Keep a steady supply
Running out of tablets is one of the most common reasons for missed doses. Refill your prescription well before the strip runs out, and carry a few spare days' supply when you travel.
Tell every doctor you see
Dentists, family doctors and specialists should know you take hormone therapy, so they can avoid medicines that interact and watch for relevant side effects.
Keep up the checks
Regular reviews, mammograms, and bone scans for aromatase inhibitors remain important even when you feel well. They are part of what makes years of treatment safe.
Commonly believed
What people assume about tamoxifen and aromatase inhibitors
Aromatase inhibitors are always better than tamoxifen.
After menopause they are slightly more effective for most women, but before menopause they only work with ovarian suppression. Tamoxifen remains a very effective choice.
If my periods stopped during chemotherapy, I am postmenopausal.
Periods can return after chemotherapy. Your oncologist may check hormone levels or add ovarian suppression before using an aromatase inhibitor.
Switching tablets means the first one failed.
Switching is common and often planned, or made to ease side effects. It does not mean the treatment stopped working.
Generic tablets are weaker than the brand.
Approved generic hormone tablets contain the same active drug. Ask your pharmacist or team if you have concerns about a product.
Questions we are asked
Common questions about choosing a hormone tablet
Can I switch if side effects are bad?
Often yes. Switching between aromatase inhibitors, or between an aromatase inhibitor and tamoxifen, sometimes eases side effects. Discuss it with your oncologist rather than stopping on your own.
How long will I take the tablet?
Usually at least five years, sometimes longer for higher-risk cancers. Your oncologist will review this over time.
Do I need a bone scan?
Usually yes before and during aromatase inhibitor treatment, because these tablets can thin the bones.
Do some medicines interact with tamoxifen?
Some antidepressants and other medicines can reduce how well tamoxifen works. Give your team a full list of everything you take.
Can men take these tablets?
Men with hormone-sensitive breast cancer usually take tamoxifen. Aromatase inhibitors are used in men only with additional treatment.
What time of day should I take it?
At the same time each day, whichever suits your routine. Consistency matters more than the exact time.
Is it safe to take ayurvedic or herbal remedies?
Some may contain plant oestrogens or interact with treatment. Ask your team before taking any.
Where can I read about my own tablet?
Your oncology team will give you written information about your hormone therapy. Use that as your main reference.
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Sources
- Early Breast Cancer Trialists' Collaborative Group — Aromatase inhibitors versus tamoxifen in early breast cancer (The Lancet)
- National Cancer Institute — Hormone therapy for breast cancer
- Cancer Research UK — Hormone therapy for breast cancer
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.