Mary Poupon, PMHNP

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Rebecca Kostopoulos, PMHNP

Director, Psychiatric Nurse Practitioners

Rebecca Kostopoulos, PMHNP, is a board-certified psychiatric nurse practitioner dedicated to helping people struggling with mental health concerns find ways to live a full and balanced life. Rebecca's practice focuses on medication management. Typically, she offers this in conjunction with supportive or emotionally focused therapy during 30-minute follow-up visits. However, occasionally Rebecca may believe that additional therapy is also needed and ask that you bring a therapist into your care team to provide the best outcome. She received her Master of Science in Nursing with a specialty in psychiatry from Columbia University and her Bachelor of Science in Nursing from Boston College. She is trained in psychiatric diagnosis, medication management, and psychodynamic and cognitive-behavioral therapies. Rebecca has extensive experience evaluating and treating adults in a variety of settings over the past 10 years. Previously, she worked at Elmhurst Hospital's Comprehensive Psychiatric Emergency Program and at Gracie Square Hospital in an inpatient unit, in addition to community health settings and skilled nursing facilities. As a nurse practitioner, she believes that addressing mental health concerns is just as important as addressing physical concerns. She values the therapeutic relationship with a collaborative and empathic approach to treatment.

Catherine Sheahan, PMHNP

Staff Nurse Practitioner

Cate Sheahan, nurse practitioner, is dual certified in psychiatry and family medicine. She completed her masters in nursing education at East Carolina University, her post graduate training in family medicine at Duke University and her post graduate training in psychiatry at the University of St. Joseph. Cate has practiced in a variety of settings including clinics, skilled nursing and assisted living facilities, hospitals and community outreach. She appreciates how her years of varied experience have enriched her practice and compassion for others. She enjoys teaching and assisting others to build on their unique experiences and strengths.

Cate believes we are each unique in our experiences and our expression of those experiences. Using a collaborative approach, she seeks to discover, along with you, her patient, what is going on in your life and deciding together what treatment is best suited for you. Cate believes medication can be a solid foundation or a transitional step toward improved mental health. She also believes in 'less is more' when it comes to medications.

During each 30-minute session, Cate will employ supportive, motivational and reframing among other therapeutic techniques to foster confidence, insight and healing as you navigate your mental health journey. She believes the mind, body and spirit are an integrated whole and therefore encourages holistic self-care such as healthy eating, good sleep hygiene, regular exercise and mindfulness practices as part of your treatment. If more intensive therapy is needed, Cate will work with your therapist or make appropriate referrals as needed.

Jaime Sather, PMHNP

Staff Nurse Practitioner

Jaime Sather, PMHNP is a board certified psychiatric nurse practitioner with over 20 years' experience in the mental health field. Specialty areas include ADHD, anxiety, depression, mood disorders, substance abuse, PTSD, and women’s health. Clinical experience with inpatient, outpatient, detoxifications rehab, psychiatric emergency department, IOP, and PHP.

Comprehensive psychiatric evaluations, medication management, and brief psychotherapy are provided. Besides medication management with psychotherapy, individual therapy may be recommended for the best possible patient outcome.

Patients feel comfortable discussing their concerns in a non-judgmental therapeutic environment. Education is provided about diagnosis and treatment options with the patient being empowered to be an active part of their treatment plan.

Maria Lourdes Castineira Garcia, MD

Staff Psychiatrist

Dr. Castineira Garcia is a highly experienced, board-certified psychiatrist specializing in adult and addiction psychiatry, with nearly 20 years of clinical experience in both English and Spanish. Originally from Galicia, Spain, she earned her medical degree from the Facultad de Medicina y Odontología in Santiago de Compostela. After several years as a primary care physician in her home region, she moved to the United States, where she was able to pursue her true passion: psychiatry. Dr. Castineira Garcia has provided high-quality care to culturally diverse communities, working in public sector, non-profit, and for-profit organizations. She has extensive experience helping patients with depression, anxiety, PTSD, and various other mental health conditions.‍Taking a personalized approach to treatment, Dr. Castineira Garcia considers the unique psychology, biology, and lifestyle of each individual when determining the best course of action. Her practice focuses on medication management in conjunction with supportive therapy, conducting follow-up visits in 30-minute increments. She believes that the most successful treatments integrate physical health, therapy, mindfulness, and medication�when necessary�to provide the most effective solutions for her If you are looking for a compassionate and experienced psychiatrist who is fluent in both English and Spanish, Dr. Castineira Garcia is an excellent choice for those seeking to improve their mental health patients.

Margaret Ngumi, PMHNP

Staff Psychiatrist

Margaret Ngumi, MSN, APRN, FNP-C, PMHNP-BC, is a dual board-certified Psychiatric Mental Health and Family Nurse Practitioner with over 20 years of experience in healthcare. She began her career as a Family Nurse Practitioner before recognizing the urgent need for accessible mental health services. This led her to pursue a post-master’s certification in psychiatry, allowing her to provide comprehensive psychiatric care. Margaret has extensive experience treating patients in both inpatient and outpatient settings, addressing conditions such as depression, anxiety, PTSD, mood disorders, and substance use disorders.

Margaret believes in a collaborative, patient-centered approach to mental health care. She strives to create a safe and supportive space where patients feel heard and empowered to take an active role in their treatment. With a strong emphasis on holistic care, she considers all aspects of a patient’s well-being, including lifestyle, relationships, and overall health. Whether through medication management, therapy, or lifestyle modifications, she is committed to helping patients achieve meaningful and lasting improvements in their mental health.

Margaret begins with a comprehensive psychiatric evaluation to understand each patient’s history, concerns, and treatment goals. She then works closely with them to develop an individualized care plan that may include medication management, therapy, and evidence-based lifestyle interventions. She prioritizes open communication, patient education, and ongoing collaboration to ensure that treatment remains effective and evolves with each patient's needs. Through her compassionate and evidence-based approach, Margaret is dedicated to helping patients find balance and improve their overall quality of life.

Gabrielle Kull, LPC

Staff Therapist

Gabrielle Kull is a Licensed Professional Counselor with a strong foundation in mental health care. She earned her undergraduate degree from Indiana University of Pennsylvania in 2017 and went on to complete her Master's degree at West Virginia University in 2019. Since then, Gabrielle has gained experience working with diverse populations and age groups while working for a non-profit organization that served victims of sexual assault, domestic violence, and other violent crimes. She has a genuine interest in treating a vast array of psychiatric disorders including Post-Traumatic Stress Disorders, Depression, Anxiety, and Obsessive-Compulsive related disorders. Gabrielle became licensed in 2022. She has been trained extensively in Eye Movement Desensitization and Reprocessing (EMDR) therapy since 2019 and achieved her EMDR certification in 2025. She takes a trauma-informed, client-centered approach, meeting individuals where they are in their healing journey. Her practice incorporates evidence-based modalities, including Cognitive Behavioral Therapy (CBT), Internal Family Systems (IFS), and mindfulness techniques, to support her clients in achieving their goals. Gabrielle is committed to ongoing education and continuous learning to ensure she provides the most effective and up-to-date care for her clients. She is currently expanding her specialties to include mental performance counseling with athletes.

Sarah Debrey, MD

Staff Psychiatrist

Dr. Debrey is board-certified in adult psychiatry. Her approach is client-centered, individualized, and collaborative. She focuses on building a strong therapeutic alliance with each client to work towards achieving enhanced functioning and meaning in their lives. She works with individuals experiencing a wide range of mental health concerns, including depression and other mood concerns, bipolar spectrum illnesses, OCD, PTSD, anxiety disorders, and substance use disorders. Though she specializes in medication management, she believes in an integrative and comprehensive treatment program that incorporates multiple aspects of an individual's health and wellness. Along with discussing physical health concerns, diet, exercise, personal connection, and stress management, she incorporates various therapeutic modalities, including CBT, DBT, ACT, and mindfulness, into her work. In some instances, Dr. Debrey may recommend more intensive psychotherapy with a collaborating therapist in order to help facilitate the best care possible. Dr. Debrey received her medical degree from Rush Medical College. She also holds a graduate degree in epidemiology from the Johns Hopkins Bloomberg School of Public Health. Following medical school, she completed her residency in psychiatry at Emory University School of Medicine. During her final year of residency, she served as chief resident at Grady Memorial Hospital. Prior to joining Talkiatry, Dr. Debrey was an assistant professor at Emory University Department of Psychiatry, where she worked as an attending psychiatrist at Grady Behavioral Health. While at Grady, Dr. Debrey worked primarily as a community psychiatrist with a focus on working with individuals experiencing psychosis. She also frequently worked on the inpatient psychiatry service at Grady. As an Emory faculty member, teaching and mentorship were an especially meaningful part of her work.‍

Menachem Liss, DO

Staff Psychiatrist

Dr. Liss was born and raised in a neighborhood in the North Bronx. He attended Queens College, CUNY where he graduated Summa Cum Laude with a B.A. in Hebrew. He completed Medical school at NYIT College of Osteopathic Medicine in Old Westbury, NY and thereafter was accepted to NUMC for psychiatry residency training. For his final year of residency training Dr. Liss was appointed to the position of Chief Resident for Academics & Research for the Psychiatry residency program at NUMC, Nassau University Medical Center. He received two awards during his residency training, including the Acute Mental Health Services Award and the Ambulatory Mental Health Services Award at the end of his 2nd and 3rd years of residency training, respectively. At NUMC, Dr. Liss underwent a rigorous training in a multitude of psychiatric settings and has experience with managing a wide array of psychiatric areas of treatment including mood/bipolar disorders, ADHD, depression, anxiety, personality disorders, as well as the intersection of medical disorders and psychiatric disorders. For his outpatient practice, Dr. Liss anticipates focusing on mood disorders, anxiety disorders, OCD, personality disorders, and family dynamics .Dr. Liss' practice focuses on a duality of treatment strategies: specifically psychotropic medication management in conjunction with non-pharmacologic treatment modalities including supportive psychotherapy, emotive supportive psychotherapy, as well as personalized variants of psychodynamic/interpersonal psychotherapy. Additionally, Dr. Liss has experience facilitating the coordination of psychosocial treatments in underserved populations.‍

Anita Green, LPC

Staff Therapist

Anita Green is a Licensed Mental Health Counselor who has worked directly with clients of various demographics and has a variety of mental health challenges. Anita graduated from Texas Wesleyan University in 2014 with a 3.8 GPA in Counseling. She also had the pleasure of studying abroad in Australia and China. Anita has been practicing as a LPC since 2023, focusing on substance abuse disorders and mood disorders that have a direct impact on everyday life. When working with Anita, her treatment will be tailored to the needs of the individual and their struggles. She uses foundational Interventions, including Addiction Counseling, CBT, DBT, ACT, EMDR, Empathy Active Listening, Crisis Intervention, Client Assessment, Therapeutic Boundaries, Self-Care Practices, and Multicultural Competence. Let's take this journey together.

Tiffany Reilly, LMHC

Staff Licensed Mental Health Counselor

Tiffany Reilly is a Licensed Mental Health Counselor with 8 years of experience providing therapeutic services to children, adolescents, and families in Seattle and New York City. She received her Master's in Counseling from Northwest University in 2015. Before coming to Talkiatry, Tiffany worked as a Family Therapist and Supervisor at Children's Aid. This role gave her experience navigating the complexities of adolescence, young adulthood, marriage, and other interpersonal stressors. She was also able to pursue additional trainings in motivational interviewing, trauma systems, and LGBTQIA supportive counseling. Tiffany focuses on treating mood and anxiety disorders, as well as the complexities of grief and loss. She has additional experience working with trauma, conduct disorder, ODD, and personality disorders. She utilizes a variety of therapeutic modalities including Cognitive Behavior Therapy, Psychoanalytic Theory, and Person-Centered Counseling. Tiffany approaches each therapeutic relationship with empathy and compassion, understanding the uniqueness of personal experience. She believes that all behavior maintains something for each individual and that when we bravely uncover our patterns, we can use our inherent strengths to work towards change.

John Bellavia, MD

Staff Psychiatrist

Dr. Bellavia is an experienced board-certified psychiatrist who specializes in adult psychiatry. He was a faculty member of the University of Washington School of Medicine in Seattle for 8 years and has been a medical director and attending psychiatrist in several clinical settings including academic medical centers, outpatient private practice and consultation. Dr Bellavia works collaboratively with each patient to identify presenting problems and stressors and utilizes evidence-based medication treatments along with individualized supportive and short-term psychotherapy strategies to reduce symptoms and improve function. If clinically indicated, he may recommend adding a psychotherapist to your care team. Dr. Bellavia has a particular interest in treating psychiatric conditions including, but not limited to, depression and bipolar disorders, ADHD, anxiety disorders, and adjustment problems. He has extensive experience working with individuals from diverse backgrounds, such as university students, creative and tech professionals, and expat communities. He uses a relaxed, nonjudgmental, empathic approach that is holistic and considers the biological, psychological, social, and cultural factors that impact mental well-being.

Thomas Spina, MD

Staff Psychiatrist

Dr. Thomas Spina is an adult psychiatrist who began his practice at Talkiatry after completing his psychiatry residency at the Eastern Long Island branch of Stony Brook University, where he treated a diverse patient population. Dr. Spina received his undergraduate degree from St. John's University in Queens where he studied Philosophy. Initially interested in a career in law, Dr. Spina decided to change gears and pursue a career in medicine after watching a relative struggle with her diagnosis of Diabetes Mellitus. Dr. Spina then completed medical school at Tel Aviv University in Israel, where he fell in love with psychiatry during his clerkship at Ichilov medical center. During that rotation, he came to appreciate how each patient has his or her own unique story, regardless of their diagnosis. Dr. Spina favors a holistic and integrative approach to psychiatry, combining medication management with supportive therapy, elements of cognitive behavioral therapy, while remaining open to other treatment modalities depending on the needs of his patients. When more focused therapy is indicated, Dr. Spina may recommend that his patient work with a provider specializing in a particular modality of therapy as part of their treatment. Dr. Spina treats adult patients with mood disorders including major depressive disorder and bipolar disorder, anxiety spectrum disorders, OCD, PTSD and specific phobias. In his spare time, Dr. Spina enjoys a variety of hobbies, including Brazilian Jiu-Jitsu, running, baseball, and exploring new eateries and shops.

Mary Poupon, PMHNP

Education and training

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