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Sarah J. Zielsdorf MD, MS, ABIM, IFMCP
February 18, 2026 1 min read
Founder & Medical Director, Motivated Medicine Internal Medicine | Functional & Precision Medicine Specialist
Functional & Internal Medicine Expertise
Dr Sarah Zielsdorf is an Institute for Functional Medicine Certified Practitioner (IFMCP) and board-certified in Internal Medicine. As the Founder and Medical Director of Motivated Medicine in West Chicago, Illinois, she leads an innovative consultative practice dedicated to uncovering root causes of chronic disease. With a strong background in microbiology and advanced diagnostics, Dr Z is widely recognised for her analytical precision and comprehensive approach to complex medical cases.
Chronic Illness & Hormone Health Specialist
Dr Zielsdorf specialises in the treatment of chronic, autoimmune-driven conditions and women’s health, with particular expertise in hormone management, including thyroid, adrenal, and sex hormone optimisation. Her work integrates conventional internal medicine with cutting-edge functional strategies to provide highly individualised treatment plans tailored to each patient’s biology.
Low Dose Naltrexone Research & Education Leadership
Dr Zielsdorf serves as Medical and Research Advisor and Education Director for the Low Dose Naltrexone (LDN) Research Trust. She teaches internationally and is the creator of the 2020–2026 LDN Guides. An author featured in The LDN Book (Volumes 2–4) and New Horizons, she is a respected voice in the advancement of LDN therapy worldwide.
Advocate for Translational & Compounded Therapeutics
A tenacious advocate for precision medicine and compounded therapeutics, Dr Zielsdorf maintains strong collaborations with compounding pharmacies throughout North America. Her Motivated Medicine model is rooted in Translational Medicine—bridging global clinical research with direct patient care—while embracing data-driven treatment, whole-body wellness, and the best of conventional medicine.