Medical Oncologist
CION Cancer Clinics
Side effects of preventive hormone medication | CION Cancer Clinics
Tamoxifen, raloxifene and aromatase inhibitors can lower breast cancer risk, but most women notice some side effects. For most they are mild and manageable, and a few are serious enough to act on the same day. This page explains which effects come with which medicine, what helps, the warning signs that cannot wait, and why stopping is a reasonable choice. At CION Cancer Clinics, our team helps carriers and their families plan checks, next steps and support after a genetic result.
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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
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On this page
- What side effects do preventive hormone tablets cause?
- Which side effects come with which medicine?
- What should I do if side effects start?
- Common side effects and what usually helps
- What this page cannot tell you
- Four things women tell us about preventive tablets
- Common questions about side effects of preventive medication
The short answer
What side effects do preventive hormone tablets cause?
Most women get some side effects, and for most they are mild and manageable. Hot flushes, vaginal changes and joint aches are the common ones. A small number of women get rarer, serious effects such as blood clots, which is why these medicines are only started after a careful check of your health.
Why side effects weigh more in prevention
When a medicine treats cancer, people accept more side effects to get well. When a healthy person takes a tablet to lower a future risk, the balance is different. You are giving up some comfort now for a lower chance of cancer later. Only you can judge whether that trade feels worth it. Many women stop quietly because they do not want to trouble the doctor or worry the family. Please tell someone instead, because most problems have a fix.
What the evidence covers
Most of what is known comes from large trials in women at raised risk for many reasons, not only gene carriers. Side effects are well described. How much benefit a carrier gets may differ by gene, and studies in carriers alone are smaller. Your oncologist can explain what is known for yours. For women with a BRCA1 fault, most breast cancers are not fed by oestrogen, so hormone tablets may help less. That is one reason medication is discussed differently for each gene.
Stopping a preventive medicine because of side effects is a legitimate choice. It is not a failure.Medicine by medicine
Which side effects come with which medicine?
Three kinds of hormone tablet are used to lower breast cancer risk. Each has its own pattern of side effects.
Tamoxifen
Can be used before or after menopause. It blocks oestrogen in breast tissue.
What women notice
- Hot flushes and night sweats
- Vaginal discharge or dryness
- Irregular or missed periods
Rarer and serious: blood clots, stroke, cataracts and, in women past menopause, womb cancer.
Raloxifene
Used only after menopause. It also helps protect bones. Hot flushes and leg cramps are common. Blood clots are the main serious risk, and unlike tamoxifen it does not raise womb cancer risk. Because it strengthens bone, it can suit a woman whose bones are already thinning.
Aromatase inhibitors
Used only after menopause. They lower the amount of oestrogen the body makes. Joint aches and stiffness are the most common complaint, and they can thin the bones, so a bone scan is usually checked. Anastrozole and exemestane are the two tested for prevention. Hot flushes and vaginal dryness also occur.
What they share
All three are usually taken for several years. Most side effects ease once the tablets stop, while much of the protection seems to last beyond the course. Side effects are often worst in the first months and settle for many women.
Before you start, expect questions on
- Any past blood clot or stroke
- Pregnancy plans and contraception
- Every other medicine you take
- Your bone health
Not sure whether this applies to you?
Ask an oncologistIf it happens to you
What should I do if side effects start?
Write down what and when
Note each symptom, when it started and how much it affects sleep, work or family life. A short record makes the follow-up visit far more useful than a vague memory.
Tell your doctor before you stop
Stopping is not dangerous in itself, but your doctor may have a simple fix. Some symptoms have other causes that are worth checking.
Try the practical fixes
Many side effects ease with simple measures, a change in the time you take the tablet, or a short break agreed with your doctor.
Switch or stop if it is not working for you
You may be able to change to a different medicine or a lower dose. If none suits you, stopping and relying on screening is a reasonable plan.
!
Signs that cannot wait
Tamoxifen and raloxifene can cause blood clots. If you develop a painful, swollen calf, sudden chest pain, sudden breathlessness, or a drooping face or weak arm, go to the nearest emergency department the same day and say which tablet you take. Any vaginal bleeding after menopause while on tamoxifen needs a doctor within days, not at your next routine visit.
Side by side
Common side effects and what usually helps
Side effect
What usually helps
Hot flushes and night sweats
Layered cotton clothing, a fan, less alcohol, non-hormonal medicines
Joint aches on aromatase inhibitors
Regular activity, simple pain relief, or switching medicine
Vaginal dryness or discomfort
Vaginal moisturisers used regularly and lubricants during sex
Leg cramps on raloxifene
Gentle stretching; tell your doctor if they persist
Low mood or poor sleep
Tell your doctor early; talking support helps many women
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Being straight with you
What this page cannot tell you
It cannot tell you which side effects you will get, or how strongly. Two women on the same tablet can have completely different experiences. It also cannot weigh the benefit for your gene against the effects you are living with. That conversation belongs with your oncologist.
It cannot check your other medicines
Some antidepressants can weaken tamoxifen, and blood thinners, hormone treatments and herbal products can all matter. Tell your doctor and pharmacist about everything you take, including ayurvedic and homeopathic remedies. Bring the strips or bottles to your appointment rather than trying to remember the names, because many brands in India contain the same medicine under different labels.
Who this does not apply to
These medicines are not usually suitable if you have had a blood clot or stroke, or if you are pregnant or planning a pregnancy, because tamoxifen can harm a developing baby. If you are taking hormone tablets as treatment after breast cancer, your treating team will guide you on side effects. What your specific variant means is a question for the counsellor who ordered the test.
Commonly believed
Four things women tell us about preventive tablets
"If I get side effects, the medicine is harming me."
Most side effects are a sign the medicine is acting on hormones, not a sign of damage. Serious effects are uncommon and have clear warning signs, which are listed on this page.
"These tablets are chemotherapy."
They are hormone tablets taken once a day at home. They do not cause hair loss or the sickness people link with chemotherapy, and you can work and travel normally.
"Once I stop, all the protection is lost."
Trials suggest much of the benefit continues for years after a full course. Stopping early gives less protection, but it is still your choice to make.
"I should put up with anything, because cancer is worse."
You are healthy, and quality of life matters. If side effects are hard to live with, say so. There are usually other options, including screening alone.
Questions we are asked
Common questions about side effects of preventive medication
How soon do side effects start?
Hot flushes and vaginal changes often start in the first few weeks. Joint aches on aromatase inhibitors can build more slowly over the first months. Many women find symptoms ease with time, so an early review is useful before deciding to stop.
Will tamoxifen stop my periods?
It can make periods irregular or lighter, and sometimes they stop for a while. Tamoxifen is not a contraceptive, and pregnancy is still possible. Use a non-hormonal method, such as a copper coil or condoms, while you take it.
Can I get pregnant after stopping tamoxifen?
Yes. Tamoxifen does not usually harm fertility in the long run. You will be advised to wait a while after the last tablet before trying, so the medicine has cleared. Plan the timing with your doctor.
Do these tablets cause weight gain?
Trials have not shown a clear weight gain from tamoxifen compared with dummy tablets. Many women gain weight around menopause for other reasons. Staying active helps with weight, mood and joint stiffness.
Will I need extra tests while I take them?
On aromatase inhibitors, a bone density scan is usually checked. On tamoxifen, any unexpected vaginal bleeding is checked promptly. Your regular breast screening continues as before. Your doctor will tell you what else suits your health.
Can I take ayurvedic or herbal remedies alongside?
Some herbal products act on hormones or on the liver, and a few can interfere with these tablets. Always tell your doctor what you take, including remedies you think of as natural or harmless.
What if I decide the side effects are not worth it?
That is a reasonable decision. Talk it through first, because a switch or a lower dose may help. If you stop, screening continues and other options remain open to you later.
Who should I call about a side effect?
For anything on the red-flag list, go to an emergency department. For other side effects, contact the doctor who prescribed the tablets. Call the CION helpline if you are not sure who to approach, and someone will point you to the right person.
Your Specialists
Meet CION's oncologists. Bring your family history or genetic report to them.
Our medical oncologists see people with a strong family history of cancer, arrange genetic counselling and testing where it fits, and plan the checks that follow.
Medical Oncologist
Dr. C. Raghavendra Reddy
MBBS(Gold Medal), DNB(General Medicine), DM(Medical Oncology)(Gold Medal)
Medical Oncologist
Dr. Bharati Devi Gorantla
MBBS, MD(General Medicine), DM(Medical Oncology)(Adyar,Chennai), ECMO, MRCP SCE(UK)
Medical Oncologist
Dr. Owais Mohammed
MBBS, MD (General Medicine), DrNB (Medical Oncology), ECMO, MRCP SCE (Medical Oncology) (UK)
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Sources
- National Cancer Institute — Breast Cancer Prevention (PDQ) - Patient Version
- NHS — Tamoxifen
- NHS — Anastrozole
- NICE — Familial breast cancer: classification, care and managing breast cancer and related risks (CG164)
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.
Keep reading
Related pages
Tamoxifen and raloxifene for risk reductionHow the two most used tablets work and who they suitAromatase inhibitors for preventionThe option for women past menopauseChemoprevention explainedWhat taking a medicine to lower risk actually meansDeciding not to act on a genetic resultWhen screening alone is the right plan for you
Talk to us
Struggling with side effects from a preventive tablet?
Tell us which medicine you take and what you are noticing. We will help you reach the right doctor to review it, whether that means a fix, a switch or stopping. One helpline serves every CION centre.