Introducing our Team of Experts
Passionate Professionals Committed to Your Wellbeing
Kory Stassi
Owner
In 2023, Dr. Stassi began his TRT journey and was amazed by the results. Inspired by his own experience, he set out to create a clinic where others could benefit from the transformative effects of testosterone replacement therapy and peptide therapy. By 2024, the idea had taken shape, and in March 2025, Optimal Performance by Stassi became a reality. As the owner and operator, Dr. Stassi has built a team of top-tier providers and staff, dedicated to delivering the highest level of care and an unparalleled patient experience.
Mary Brooks, MSN, APRN, FNP-C/PMHNP-BC, FPA
Nurse Practitioner
Mary’s nursing career began in 2010 when she first became a Registered Nurse. In 2017 She graduated from Maryville University in St. Louis, MO with my master’s degree in nursing and became a board-certified Family Nurse Practitioner (FNP-C) licensed in Illinois. She has been blessed to work in many facets of healthcare since and has also become a board-certified Psychiatric Mental Health Nurse Practitioner (PMHNP-BC). With a strong foundation in both primary care and mental health, she brings an approach that aligns overall wellness and hormone optimization with physical, mental, and lifestyle well-being.
She has extensive experience caring for adults across the lifespan and am passionate about helping patients feel their best through individualized, evidence-based treatment plans. My clinical focus includes hormone replacement therapy, mood and energy concerns, stress management, metabolic health, and overall wellness optimization.
By integrating physical health, mental well-being, and lifestyle factors, she partners closely with patients to identify root causes, educate them on their options, and support sustainable improvements in quality of life. Known for a thoughtful, compassionate, and collaborative approach, she is committed to creating a safe, supportive environment where patients feel heard and empowered in their care.
Tommi Thien
Clinic Operations Director
Tommi joined the Stassi team in August of 2017 and has played a vital role in ensuring the smooth operation of the office. With extensive experience in patient care and office management, Tommi handles day-to-day office activities, ensuring that both administrative and patient-related processes are efficiently managed. Her attention to detail and commitment to the team make her an essential part of the practice's success.
Graduating with a business degree from Eastern Illinois University, Tommi has developed a strong foundation in organizational skills and business management, which she applies daily in her role. Outside of work, she is a devoted mother to her two children, Noah and Bella, and wife to Jacob. She has a passion for reading, traveling, and spending quality time with her family. With a dedication to both her professional and personal life, Tommi ensures that Optimal Performance by Stassi and Stassi Chiropractic runs smoothly and that patients and staff have a positive and efficient experience.
