Michael O'Brien, M.D.
NPI 1821181215 · Family Medicine Physician · Castro Valley, CA
Michael O'Brien, M.D. is a Family Medicine Physician provider in Castro Valley, CA (NPI 1821181215).
Provider details
- NPI number
- 1821181215
- Entity type
- Individual
- Primary specialty
- Family Medicine PhysicianAllopathic & Osteopathic Physicians
- Credential
- M.D.
- Sex
- Male
- Sole proprietor
- Yes
- License
- G61152 (CA)
Specialties & taxonomies
Allopathic & Osteopathic Physicians
Profile Score
A profile completeness & documented-activity index — NOT a quality, outcomes, or patient-satisfaction rating.
- Registry tenure33% of score
19 yrs in NPPES registry
- Profile completeness33% of score
100% of core fields populated
- Practice footprint20% of score
1 documented practice location
- Open Payments transparency13% of score
Has Open Payments disclosures (2024)
Signals a provider has no public data for (e.g. Medicare claims) are left out of the score entirely — never counted as zero — so providers without that data are not penalized. See the full formula and weights in our methodology.
What this provider prescribes (Medicare Part D)
Top drugs by Medicare Part D claim volume, 2024 · 17 distinct drugs on file.
| Drug | Part D claims (2024) |
|---|---|
| Atorvastatin Calcium | 34 |
| Donepezil Hcl | 24 |
| Memantine Hcl | 23 |
| Allopurinol | 23 |
| Tamsulosin Hcl | 21 |
| Pantoprazole Sodium | 17 |
| Sertraline Hcl | 17 |
| Metoprolol Succinate | 16 |
| Mirabegronbrand: Myrbetriq | 16 |
| Gabapentin |
Transparency — industry payments
Based on CMS Open Payments, 2024; not all care is captured.
$34 across 1 record (Open Payments 2024)
Open Payments discloses payments and transfers of value (meals, travel, consulting, research, royalties) from drug and device makers to providers. This is a transparency signal, not a verdict — such payments are legal and common, and their presence is neither an endorsement nor a criticism. Source: CMS Open Payments, program year 2024.
Practice location
Mailing address
Registry dates
- Enumerated
- 2006-09-30
- Last updated
- 2007-08-21
Frequently asked questions
- What is Michael O'Brien's NPI number?
- Michael O'Brien's National Provider Identifier (NPI) is 1821181215, a unique 10-digit ID issued by CMS for use in standard healthcare transactions.
- What is Michael O'Brien's specialty?
- Michael O'Brien is listed in the NPPES registry with a primary specialty of Family Medicine Physician (Allopathic & Osteopathic Physicians).
- Where is Michael O'Brien located?
- Michael O'Brien's practice location on file with NPPES is 20100 Lake Chabot Rd, Castro Valley, CA 94546-5306.
- What is Michael O'Brien's phone number?
- The practice phone number listed in the NPPES registry for Michael O'Brien is (510) 581-7677.
- Is Michael O'Brien's NPI active?
- Yes — Michael O'Brien's NPI (1821181215) is active in the NPPES registry as of the last update on 2007-08-21.
Source: CMS NPPES Data Dissemination (June 2026). NPI Central is not affiliated with CMS. Data is provided as-is from the public registry.