HealthcareDiscovery.AI / Doctors / California / Ontario / Internal Medicine

Internal Medicine in Ontario, California

Data updated monthly · Last refresh September 2026

8 Internal Medicine providers practice in Ontario. Listings are drawn from federal public records and are not endorsements.

Internal Medicine providers in Ontario

Listed alphabetically. Payment figures come from the federal Open Payments program, which requires drug and device companies to report what they pay physicians for consulting, speaking, meals, travel and royalties. A disclosed payment is a financial relationship, not evidence of wrongdoing, and many totals reflect a single meal. Figures cover calendar year 2025.

Dr. David Daniels, MD
Ontario, CA · $28 in drug and device payments (2025) · (909) 941-2572
Dr. David Hirota, M.D.
Ontario, CA · No drug or device payments recorded (2025) · (909) 566-0445
Dr. Dianne Quintana, M.D.
Ontario, CA · $71 in drug and device payments (2025) · (909) 469-9013
Dr. Eric Gureghian, MD
Ontario, CA · No drug or device payments recorded (2025) · (909) 605-8000
Dr. Kishan Thapar, M.D.
Ontario, CA · No drug or device payments recorded (2025) · (909) 932-1045
Dr. Liwanag Asuncion, M.D.
Ontario, CA · No drug or device payments recorded (2025) · (440) 225-7095
Dr. Rodman St. Clair, M.D.
Ontario, CA · No drug or device payments recorded (2025) · (909) 605-8015
Dr. Yan Zhang, MD
Ontario, CA · $15 in drug and device payments (2025) · (626) 991-0668

Conditions Internal Medicine providers in Ontario, California commonly treat

Patients often search by condition rather than specialty. These are conditions typically managed by Internal Medicine providers. Individual practices vary, so confirm with the provider before booking.

Common questions

How many Internal Medicine providers are in Ontario, California?

There are 8 Internal Medicine providers with active NPI records practicing in Ontario, according to federal NPPES data refreshed monthly.

What conditions do Internal Medicine providers in Ontario treat?

Internal Medicine providers in Ontario commonly treat high blood pressure, type 2 diabetes, high cholesterol, preventive care, chronic disease management and related conditions. Individual practices vary, so confirm with the provider before booking.

Where does this data come from?

Provider records come from the federal NPPES registry and CMS Doctors and Clinicians files. Payment figures come from the CMS Open Payments program for calendar year 2025. The directory refreshes monthly.

All specialties in Ontario Internal Medicine across California

Try a city like Tucson, a zip like 85016, or a specialty like psychiatry. For a doctor by name, use the full search.
Sources: NPPES (CMS), Doctors and Clinicians national files, CMS Open Payments 2025. Updated monthly. Records are public federal data and are not verified credentials, licensure checks, or endorsements. This directory is informational and not medical advice. How we build this directory.