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Vesna Pirec MD, PhD

Board Certified Psychiatrist, Chief Medical Officer


Dr. Vesna Pirec has extensive experience with behavioral health issues specific to reproductive cycles in women, including perinatal mental health and postpartum depression, anxiety and psychosis.

Dr. Pirec received her Medical Degree at the University of Belgrade and her PhD in Pharmacology at the University of Illinois in Chicago, Department of Pharmacology.

She is the author of several textbook chapters and articles, and is a member of NASPOG (North American Society for Psychosocial Obstetrics and Gynecology) serving as Elected Board Member en Large, the Marce Sociéty for Perinatal Mental Health, Fellow Member of the American Psychiatric Association (APA), and the Illinois Psychiatric Society.  She speaks several languages, including Spanish.

Prior to joining the staff at Insight, Dr. Pirec was the Program Director of Women’s Mental Health in the Department of Psychiatry at the University of Illinois at Chicago.

Nancy Tyler, MD

Adolescent and Adult Psychiatrist


Dr. Nancy Tyler has extensive experience in mood and anxiety disorders and treatment or eating disorders in adolescents and adults. She has trained and practiced in adult psychiatry, child and adolescent psychiatry and pediatrics.

Dr. Tyler grew up in Long Island, New York and received her Bachelor’s degree from Tufts University.  She earned her MD from SUNY in Buffalo, New York, completed her pediatric residency at Columbia-Presbyterian Medical Center in New York, her psychiatry residency at Beth Israel Medical Center in New York, and her Child & Adolescent Psychiatry Fellowship at North Shore University Hospital at NYU.

Before joining Insight, Dr. Tyler was an Attending Psychiatrist at Alexian Brothers Behavioral Health Hospital where she cared for patients in the Eating Disorders and Self Injury recovery programs.  Her broad experience in a variety of settings provides a solid foundation for delivering compassionate treatment to patients at all levels of care.  Additionally, Dr. Tyler is conversant in Spanish.

Peter Zemenides, MD

Staff Psychiatrist


Dr. Peter Zemenides serves as Staff Psychiatrist for Insight Behavioral Health Centers’ Mood and Anxiety Program and Compulsive Overeating Recovery Effort (CORE). Prior to joining Insight’s medical leadership team, Dr. Zemenides served as Acting Medical Director of the McClendon Center in Washington, DC, a leading treatment center serving the needs of adults diagnosed with serious and persistent mental illness. In this role, he oversaw the assessment and management of patients with psychiatric conditions, including initial and follow up assessment, medication management, psychotherapy, ordering/interpreting diagnostic tests and coordination of care within an interdisciplinary team framework.

Dr. Zemenides served as a Clinical Case Conference Facilitator, Psychiatry Small Group Facilitator and Guest Lecturer at the George Washington University School of Medicine. He has also participated in research initiatives in the Neurology departments at both the University of Illinois Chicago College of Medicine and Northwestern University.

Dr. Zemenides speaks widely on the topic of mental illness at symposia in the United States and abroad, and has authored numerous articles on topics including psychopharmacology, behavioral analysis, psychology of terrorism, delirium and circadian rhythms.

He earned his MD and completed his Residency at the George Washington University School of Medicine following completion of his BA at Northwestern University.

Lisa Oldson, MD

Medical Director of Adult CORE


Lisa Oldson, MD is an experienced physician Board certified in both Internal Medicine and Obesity Medicine, serves as Medical Director of the Adult CORE program at Chicago-based Insight Behavioral Health Centers.

In her role at Insight, Dr. Oldson oversees the delivery of medical support and care for male and female adults (ages 18 and older) participating in obesity treatment and prevention programming.  She is passionate about helping individuals reach and maintain a healthy weight, and her unique experience fusing expertise in General Internal Medicine and Obesity Medicine helps her to effectively support patients throughout their journey.

Prior to joining Insight’s weight management programming, Dr. Oldson served as an Internal Medicine physician at Northwestern Medical Group (formerly Northwestern Memorial Physicians Group), a leading multi-specialty physician organization in the Chicagoland area. Additionally, Dr. Oldson is committed to training the next generation of physicians and has been a Clinical Instructor at Northwestern University’s prestigious Feinberg School of Medicine since 1998.

Dr. Oldson began her career at Rush Medical College in Chicago, Illinois, where she earned her medical degree and completed her residency. She served as Chief Medical Resident, Internal Medicine and was the recipient of several honors related to her clinical skill and leadership acumen.

“As an Obesity Medicine physician coming from a Primary Care background, I understand the impact of obesity on health as well as on self-esteem, employment, relationships, mood and productivity. Every day, we make a myriad of decisions about food, movement and lifestyle that impact our weight. Insight’s compassionate multidisciplinary treatment team educates and guides individuals as they navigate these decisions for themselves and their families. I’m delighted to join this comprehensive group of dedicated providers.”

– Lisa Oldson, MD

Lynn Gettleman Chehab, MD, MPH

Medical Director of AP CORE


Lynn Gettleman Chehab, MD, MPH is a Board certified, fellowship-trained pediatrician and serves as Medical Director of the Comprehensive Overeating Recovery Effort program for adolescents (AP CORE) at Chicago-based Insight Behavioral Health Centers. In her role at Insight, Dr. Chehab oversees the delivery of medically-supported obesity prevention and recovery programming for male and female adolescents (ages 12 through 17).

In addition to her work with adolescent patients in Insight’s evidence-based weight management programming, Dr. Chehab is a pediatrician at NorthShore University Health Systems and serves as a staff physician at the School-Based Health Center at Evanston Township High School. She first became interested in obesity prevention and treatment as a medical student at Stanford University, where she studied how to target low-income women for cardiovascular disease prevention. After finishing her pediatric training in San Francisco and New York, she completed a public health fellowship at the Columbia University College of Physicians and Surgeons and the Mailman School of Public Health in New York City, obtaining a Master’s degree in Public Health with a concentration in community-based pediatric obesity prevention.  While at Columbia, Dr. Chehab created a program to teach pediatric residents at Harlem Hospital how to screen for and treat obesity using simple messages. She also evaluated “Energy Up,” one of the first school-based obesity programs to focus on self-esteem and emotional eating as an important component in obesity treatment. The results of the evaluation were published in the Journal of Adolescent Medicine, and forever changed how Dr. Chehab approached obesity treatment.  Over the past 8 years, in collaboration with staff at the ETHS health center, Dr. Chehab created “6 to Success,” a clinic-based obesity program that combines simple messages with social work support to help adolescents achieve better weight management.