Caitlin Tillberg, MD

Donna is a Board-Certified Psychiatric Nurse Practitioner dedicated to breaking down mental health stigma and expanding access to compassionate, quality care. With over 20 years of nurse practitioner experience, she has supported patients and families through life’s emotional and physical challenges across outpatient, inpatient, and telepsychiatry settings. Donna is passionate about creating a safe, empowering space where individuals feel seen, heard, and valued on their mental health journey.

Donna helps patients become the best, healthiest version of themselves, both mentally and emotionally. She values open communication, mutual respect, and collaborative decision-making. Her treatment plans include medication management, healthy coping strategies, and tools to build self-awareness and resilience. Known for her warmth and empathy, Donna creates a judgment-free environment where every voice matters.

Donna begins by building trust through a compassionate, in-depth initial interview. Together with each patient, she develops a personalized treatment plan that blends medication management with lifestyle recommendations tailored to individual goals and values. Her holistic approach focuses not just on symptom relief, but on fostering lasting growth, confidence, and overall well-being.

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Dr. David Guggenheim is an experienced clinical psychologist and health care administrator. He has worked with patients at different stages of life, including children, adolescents, and adults, and he has treated patients living with a wide range of mental health conditions, including anxiety, depression, post-traumatic stress disorder (PTSD), substance use, and attention-deficit hyperactivity disorder. Dr. Guggenheim has specific training in Trauma-Focused Cognitive Behavioral Therapy, Motivational Interviewing, and foundational training in dialectical behavioral therapy. Prior to joining Talkiatry, Dr. Guggenheim served as the Chief Behavioral Health Officer at Callen-Lorde Community Health Center in New York City, specializing in LGBTQ+ health care. In that role, he oversaw teams of providers including psychiatrists, psychologists, and social workers, who collectively provided care to thousands of patients in the New York metropolitan area. While at Callen-Lorde, he also served as co-chair for the behavioral health subcommittee of the Community Health Center Association of New York State; worked as an Adjunct Professor at Post University; and performed volunteer clinical work at the Weill Cornell Center for Human Rights. Before joining Callen-Lorde, Dr. Guggenheim worked as Associate Chief Behavioral Health Officer at Community Health Center, Inc., a federally qualified health center in Connecticut. A recognized expert, Dr. Guggenheim has delivered lectures to audiences ranging from medical schools to corporate executives, and he has been quoted in national media including The Advocate, Yahoo Finance, and Teen Vogue. Dr. Guggenheim has also been honored with an Early Career Achievement Award from the American Psychological Association in 2016. Dr. Guggenheim received his Bachelor of Arts from the University of Connecticut in 2002 and his Doctor of Psychology in Clinical Psychology from the American School of Professional Psychology at Argosy University/Washington, DC in 2009.

Melissa Sims, MSN, APRN, PMHNP-BC, is a board-certified psychiatric mental health nurse practitioner who is passionate about delivering high-quality, compassionate, and comprehensive mental health care. She earned her Master of Science in Nursing from the University of Alabama at Birmingham in 2022 and has since worked in both community mental health and correctional settings.

Melissa takes a collaborative approach to care, working closely with other mental health professionals, medical providers, families, and relevant support systems to ensure well-rounded treatment. She emphasizes a patient-centered, individualized approach, combining medication management with psychotherapy to meet each person’s unique needs.

Patients working with Melissa can expect a thorough evaluation, accurate diagnosis, and a personalized treatment plan tailored to their mental health goals. One of her core priorities is to empower individuals to make informed decisions about their care by providing education grounded in research, evidence-based practices, and clinical experience.

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Dr. Gulati is a board-certified adult psychiatrist who has been in practice for over 10 years. She has worked in inpatient units, private practice, and community mental health, as well as served as Chief Medical Officer of a large psychiatric hospital. In 2018 she was awarded the Charleston Choice Award for Best Psychiatrist in Charleston, South Carolina. She currently resides in South Florida. Dr. Gulati's practice centers around treating the whole patient: mind, body, and spirit. She believes the judicious use of psychiatric medications, coupled with psychotherapy and alternative treatments such as meditation and yoga, can bring about transformative changes in the lives of those suffering from depression, anxiety, and other mental conditions and life issues. Dr. Gulati graduated with Honors in Psychology from The University of Florida, received her medical degree from The University of South Alabama School of Medicine, completed a clinical postdoctoral research fellowship at Boston University School of Medicine, and completed her Psychiatry residency training at The University of North Carolina. She is currently obtaining her MBA. After residency, she worked as a psychiatric hospitalist at Trident Medical Center in Charleston and has also worked in private practice. Most recently she served as Chief Medical Officer for an 80-bed psychiatric hospital, Coral Shores Behavioral Hospital in Stuart, FL. In addition to general adult psychiatry, Dr. Gulati received extensive training in one of the nation's largest women's mood disorder programs at The University of North Carolina Chapel Hill and enjoys treating peripartum and postpartum mood and anxiety disorders. She is also well trained in addiction medicine and received additional training in buprenorphine use for opioid addiction.

Mary Birse is a board-certified Psychiatric Mental Health Nurse Practitioner (ANCC) with over 20 years of nursing experience. She graduated magna cum laude with a BSN from Florida Atlantic University and earned her MSN from the University of Florida. She completed a Psychiatric NP Residency at the VA in Charleston, SC. Mary has worked in a variety of settings including the West Palm Beach VA Medical Center, the Palm Beach County Firefighter’s Clinic, various outpatient telehealth platforms, and a child and adolescent inpatient facility. She was also an adjunct professor at Palm Beach State College.

Mary believes in empowering patients through education and collaboration so they can play an active role in their mental health journey. She works to create a warm and welcoming space where patients feel safe, heard, and understood. Whether the treatment path includes therapy, medication, integrative approaches, or a combination, she ensures that the plan reflects the patient's needs and goals.

Mary takes a thorough and holistic approach to care. She spends time understanding each patient’s history and past treatments—what has or hasn’t worked—and listens carefully to their current concerns and future goals. By factoring in lifestyle and preferences, she works with patients to build thoughtful, individualized treatment plans.

Nicole Estevez is a licensed mental health counselor in New York and an out-of-state telehealth provider in Florida. She received her Master of Mental Health Counseling from Alliance Graduate School of Counseling (now Alliance University). Nicole has 9 years of experience providing client-centered individual and family therapy services to a wide variety of clients. Nicole has worked in a variety of settings including an outpatient community clinic, in-home family therapy, treating undocumented minors with trauma history, and telehealth. Nicole has experience working with clients who are experiencing anxiety, depression, bipolar disorder, borderline personality disorder, grief, post traumatic stress disorder, and other mental health concerns. Over the years in the mental health field, she believes that the best approach to therapy is a collaborative process with the client to assist in achieving their goals. Nicole has experience with modalities including cognitive behavioral therapy, psychodynamic, motivational interviewing, and dialectical behavioral therapy.