Understanding tamoxifen
How it works and what to expect
Sources checked: September 2026
The short version
Tamoxifen blocks estrogen from attaching to receptors on cancer cells. It can be used by people before or after menopause and is typically taken daily for several years.
Tamoxifen works by blocking estrogen from attaching to receptors on -positive cancer cells, which can help slow or stop their growth. Unlike aromatase inhibitors, it can be used by people who haven't gone through menopause as well as those who have.
- Taken as a daily pill, usually for five to ten years
- Common side effects can include hot flashes, mood changes, and irregular periods
- Rare but serious risks, like blood clots, are usually discussed before starting
When to call promptly
Contact your care team promptly about leg swelling or pain, sudden shortness of breath, or unusual vaginal bleeding while on tamoxifen.
Questions you may want to ask
Why is tamoxifen being recommended over an aromatase inhibitor for me?
What side effects are most important for me to watch for?