ESTHER WON, MD appears in the CMS NPPES registry as a Geriatric Medicine (Family Medicine) Physician provider holding MD credentials at 9961 SIERRA AVE, FONTANA, CA, 92335, with a listed phone of (909) 427-3910. NPI 1902973803 was issued on 11/29/2006. Because NPPES data is self-reported by the provider and refreshed monthly, the address, phone, and specialty reflect what WON most recently submitted to CMS rather than a vetted directory listing, which is why patients should always confirm the practice is still at this location before scheduling.

Medicare Part D records for calendar year 2023 show 989 prescription claims written by this provider, covering 99 Medicare beneficiaries and totaling roughly $69K in drug spend, with an opioid prescribing rate of 5.7%. These figures capture only Medicare Part D — commercial insurance, Medicaid, and cash-pay prescriptions are not included, and any drug-beneficiary cell under 11 is suppressed by CMS for patient privacy.

Geriatric Medicine (Family Medicine) Physician is a narrow specialty nationwide, with 1,779 enrolled providers across 52 states and an average of 4,854 Part D claims per prescriber, so the context for interpreting these metrics differs meaningfully from a primary-care baseline. Important: PlainDoctor is a directory of publicly available government data, not medical advice, a malpractice database, or a quality rating. Inclusion here does not imply a recommendation, and absence of complaints or sanctions on this page does not mean none exist — always verify credentials through the NPPES NPI Registry, your state medical board, and the ABMS or AOA before making healthcare decisions.