What Side Effects Can Tamoxifen Cause? (2026 Update)

Hormone therapy such as tamoxifen commonly causes menopause-like symptoms along with a decrease in bone density, and managing it requires attention over several years. That said, severity varies by individual, so if symptoms occur, the general principle is to adjust treatment together with your care team.

Key Takeaways

• For hormone receptor-positive breast cancer, it is common to continue hormone therapy (such as tamoxifen) for 5 to 10 years after surgery.
• Common symptoms resemble menopause—hot flashes, a feeling of joint stiffness, and vaginal dryness—and a decrease in bone density may also occur alongside these.
• When early ovarian insufficiency develops, it can bring irregular or absent menstrual periods, night sweats, mood changes, joint and muscle pain, and sleep disturbances, with osteoporosis and cardiovascular risk reported as long-term effects.
• Because treatment continues over a long period, it is recommended to regularly schedule bone density checks and gynecologic exams alongside it.
• The starting point for management is to record symptoms and report them to your care team rather than simply enduring them.

Why Do Menopause-Like Symptoms Occur With Tamoxifen?

• Hormone therapy is a drug treatment that works by blocking or reducing the action of estrogen. In breast cancers that are hormone receptor-positive, estrogen can stimulate cancer cell growth, so treatment that blocks this is continued for 5 to 10 years after surgery.
• As estrogen signaling in the body decreases during this process, menopause-like symptoms (hot flashes, a feeling of joint stiffness, vaginal dryness) commonly appear. The specific medication used differs depending on whether the patient is pre- or post-menopausal, and in some cases injections that suppress ovarian function are added.

How Much Attention Should I Pay to Decreased Bone Density?

• Because hormone therapy can be accompanied by decreased bone density, it is a general practice to manage this over several years alongside bone density testing.
• If hormone therapy leads to early ovarian insufficiency, it may come with irregular or absent menstrual periods, hot flashes, night sweats, vaginal dryness, mood changes, joint and muscle pain, and sleep disturbances, and osteoporosis and cardiovascular risk have been reported as long-term effects. For this reason, regular bone density and gynecologic exams are recommended both during treatment and after it ends.

What Steps Should I Follow if Side Effects Occur?

1. Step 1 — Record your symptoms: Writing down when each symptom started and whether it is worsening makes consultations faster and more effective.
2. Step 2 — Notify your care team: Rather than enduring symptoms, it is recommended to report any changes right away, and medication should not be adjusted on one's own.
3. Step 3 — Undergo necessary tests: Bone density tests, gynecologic exams, and other tests help confirm the cause and severity of the symptoms.
4. Step 4 — Adjust the management plan: Medication or lifestyle management approaches are determined together based on the symptoms, and whether to continue treatment is decided by the care team based on the clinical course.

FAQ — How Many Years Does Hormone Therapy Need to Continue?

For hormone receptor-positive breast cancer, it is common to continue oral hormone therapy for 5 to 10 years after surgery. Since it is an oral medication, treatment can be continued locally once a prescription and plan are received, and details of which medications to use, in what order, and when to undergo which tests can be summarized and provided in a handover document.

FAQ — Can Symptoms Continue Even After Treatment Ends?

Symptoms caused by early ovarian insufficiency can continue not only during treatment but also after it ends, and effects such as decreased bone density are areas that require long-term management. Regular bone density and related tests are recommended even after treatment has concluded.

Sources and Notes

This article was written based on breast cancer resource notes and long-term side-effect management notes (including materials from the U.S. National Cancer Institute, NCI). This content is intended for general medical information purposes only, and actual diagnosis, treatment methods, and outcomes may vary depending on individual circumstances. Please be sure to consult with your care team to determine accurate diagnosis and treatment.