About
Jonathan Rosaasen, MD earned his Doctorate of Medicine from Loma Linda University School of Medicine in 2002. He completed his internship and Family Medicine residency at Kaiser Riverside, finishing in 2005. He holds board certification from the American Board of Family Medicine and holds an active California medical license.
Dr. Rosaasen spent the early part of his career in large group and government settings before founding his own private practices in Ventura County. He served as President and Medical Director of Moorpark Family Medicine from 2008 to 2017. He currently leads Rosaasen Family Medicine, Inc. as President and Medical Director, and consults for SteadyMD. He is passionate about preventive medicine, lifestyle modification, weight loss, nutrition, and mental wellness. Dr. Rosaasen holds affiliations with Simi Valley Hospital and Los Robles Hospital. He tailors health goals to each individual patient and stays current with clinical research to help patients choose their own path toward better health.
Education & Training
Medical School
Loma Linda University School of Medicine, Loma Linda, CA - Doctorate of Medicine (2002)
Residency
Residency in Family Medicine, Kaiser Riverside, Riverside, CA (2003-2005)
Additional Training
Internship, Kaiser Riverside, Riverside, CA (2002-2003)
Certifications
Conditions Treated
Who is Dr. Rosaasen right for?
Dr. Rosaasen is a strong fit for adults who want a proactive, prevention-focused approach to their health. Patients working on weight management, nutrition, or exercise goals benefit from his hands-on guidance. He is particularly effective with individuals managing chronic conditions who prefer lifestyle-based solutions over medication. Anyone who values direct, around-the-clock access to their own physician will find his practice well suited to their needs.
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Frequently Asked Questions
Dr. Rosaasen specializes in family medicine and preventive medicine. He focuses heavily on lifestyle modification, weight management, nutrition, exercise, and mental wellness. His clinical philosophy prioritizes prevention over medication whenever possible.
Yes, Dr. Rosaasen holds board certification from the American Board of Family Medicine. He also maintains an active California medical license.
Dr. Rosaasen earned his Doctorate of Medicine from Loma Linda University School of Medicine in 2002. He then completed his internship and Family Medicine residency at Kaiser Riverside, finishing in 2005.
Dr. Rosaasen has practiced family medicine for over two decades. He served as President and Medical Director of Moorpark Family Medicine from 2008 to 2017 before launching his current practice in Ventura County.
Every appointment involves Dr. Rosaasen directly. The practice does not route patients through nurse practitioners or physician assistants. You work with Dr. Rosaasen at every visit.
Dr. Rosaasen treats chronic conditions including weight management issues, metabolic concerns, and a range of conditions managed through lifestyle intervention. He also provides comprehensive preventive care and mental wellness support.
Yes, Dr. Rosaasen holds affiliations with Simi Valley Hospital and Los Robles Hospital. When patients require inpatient care, these affiliations support continuity of care.
Dr. Rosaasen sees patients from Thousand Oaks, Moorpark, Simi Valley, and Westlake Village. His practice sits in Thousand Oaks and draws patients from across Ventura County.
Doctor profile last updated March 21, 2026