WILLIAM O'CONNOR, M.D. appears in the CMS NPPES registry as a Family Medicine Physician provider holding M.D. credentials at 300 MASON ST., VACAVILLE, CA, 95688, with a listed phone of (707) 446-0422. NPI 1639127632 was issued on 05/04/2006. Because NPPES data is self-reported by the provider and refreshed monthly, the address, phone, and specialty reflect what O'CONNOR 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 2,161 prescription claims written by this provider, covering 128 Medicare beneficiaries and totaling roughly $259K in drug spend, split 12% brand-name and 88% generic by claim count, with an opioid prescribing rate of 0.9%. 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.

Family Medicine Physician is a high-volume specialty nationwide, with 147,640 enrolled providers across 56 states and an average of 3,418 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.