Is weight gain common with tamoxifen and letrozole, and why is it hard to lose weight on hormone therapy?
Weight gain can happen with both tamoxifen and aromatase inhibitors like letrozole, though the research is mixed. Some studies suggest tamoxifen might affect thyroid function in the first year of treatment, potentially Show Full Answer
Is weight gain common with tamoxifen and letrozole, and why is it hard to lose weight on hormone therapy?
Weight gain can happen with both tamoxifen and aromatase inhibitors like letrozole, though the research is mixed. Some studies suggest tamoxifen might affect thyroid function in the first year of treatment, potentially making weight gain more likely. With aromatase inhibitors, weight gain seems more common during the first year of treatment.
Many MyBCTeam members have shared similar struggles. One member said, "Anastrozole and its alternatives make it very hard to lose weight. I've tried unsuccessfully for two years. I met with a dietitian, strictly followed her recommended diet, and exercised every day for six months. I lost only 1.5 pounds."
Another member shared, "I started tamoxifen last July and have gained 25 pounds. I walk five miles every day, and it hasn't touched it. Oh, and mine is also in the belly, where I have never ever gained weight before."
Risk factors for weight gain include:
- Being younger than 60
- Having had a mastectomy
- Smoking cigarettes
It's important to know that other factors can contribute too, like changes in activity level, menopause, or recovery from treatment. Chemotherapy alone can cause 6 to 11 pounds of weight gain.
If you're struggling with weight changes, talk to your oncology team. They can run tests to identify causes and may refer you to a registered dietitian who specializes in supporting people during breast cancer treatment.
December 27, 2025
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