Estrogen-Only Therapy May Raise Autoimmune Disease Risk

Study finds higher autoimmune incidence in women using estrogen-only hormone therapy versus combined regimens.

Updated on Oct. 23, 2026 in Women’s Health

A group of empty laboratory beakers and a pipette resting on a sterile white surface. — A study of over 100,000 women links estrogen-only menopausal hormone therapy to a higher incidence of autoimmune diseases compared to combined regimens. AI Illustration. Upload story photo >

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If you use hormone therapy, does the potential risk of autoimmune issues change your treatment view?

A large study of over 100,000 women found a higher incidence of autoimmune disease among those using estrogen-only menopausal hormone therapy compared to those on combined therapy. These findings provide new context for women navigating hormone therapy decisions with their doctors.

Why it matters

Understanding potential links between hormone therapy and immune system health is vital for women deciding how to manage menopausal symptoms. This research highlights the need to weigh the benefits of systemic hormone use against risks, particularly for those using estrogen alone after a hysterectomy.

In a retrospective study of 100,000 women ages 45 to 70, researchers observed a 4.9% incidence of composite autoimmune disease in estrogen-only therapy users compared to 4.5% in those on combined regimens. These results are considered preliminary and await further prospective validation.

The players

The Menopause Society

A non-profit professional organization dedicated to advancing research and education in women’s midlife health.

The details

The study utilized the TriNetX U.S. Collaborative Network to analyze outcomes at least 180 days after hormone therapy initiation in propensity score-matched groups of 54,692 women. While combined estrogen-progestogen therapy is standard for endometrial protection, estrogen-only therapy is often prescribed following a hysterectomy. The data showed significant hazards for specific conditions including systemic lupus erythematosus, psoriasis, psoriatic arthritis, multiple sclerosis, and lichen sclerosis in the estrogen-only cohort.

October 23, 2026: Findings were presented at the Menopause Society annual meeting.

Health Landscape

This study contributes to the evolving understanding of how menopausal hormone therapy interacts with broader systemic health. It adds to the ongoing research presented at The Menopause Society annual meeting regarding the safety profiles of hormonal treatments.

If you are currently using estrogen-only therapy, this data is worth discussing during your next checkup with your physician. Ask your care team about your specific risk factors for autoimmune conditions and whether your current hormone regimen remains the most appropriate choice.

The takeaway

Large-scale data suggests a potential association between estrogen-only hormone therapy and a slight increase in autoimmune disease risk. Discuss your specific medical history and symptom management plan with your doctor to ensure your treatment aligns with your current health needs.