Justin Mager, M.D.
NPI 1669672739 · Internal Medicine Physician · Mill Valley, CA
Justin Mager, M.D. is a Internal Medicine Physician provider in Mill Valley, CA (NPI 1669672739).
Provider details
- NPI number
- 1669672739
- Entity type
- Individual
- Primary specialty
- Internal Medicine PhysicianAllopathic & Osteopathic Physicians
- Credential
- M.D.
- Sex
- Male
- Sole proprietor
- No
- License
- A95972 (CA)
Specialties & taxonomies
Allopathic & Osteopathic Physicians
Profile Score
A profile completeness & documented-activity index — NOT a quality, outcomes, or patient-satisfaction rating.
- Registry tenure38% of score
18 yrs in NPPES registry
- Profile completeness38% of score
100% of core fields populated
- Practice footprint23% of score
1 documented practice location
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 · 3 distinct drugs on file.
| Drug | Part D claims (2024) |
|---|---|
| Losartan Potassium | 34 |
| Rosuvastatin Calcium | 24 |
| Levothyroxine Sodiumbrand: Synthroid | 13 |
Medicare Part D only. These counts cover prescriptions paid through Medicare Part D in 2024 — they do notinclude cash-pay, commercial-insurance, Medicaid, or Part B–administered drugs, and badly undercount high cash-pay categories (e.g. GLP-1 weight-loss, testosterone, and ED medications). Any drug with 10 or fewer claims is omitted by CMS, and beneficiary counts under 11 are suppressed — so a missing drug means no Part D record, never zero. This is a factual claims summary, not an endorsement, not medical advice, and not a consumer report. Source: CMS Medicare Part D Prescribers — by Provider and Drug.
Practice location
Mailing address
Registry dates
- Enumerated
- 2007-07-18
- Last updated
- 2012-11-05
Frequently asked questions
- What is Justin Mager's NPI number?
- Justin Mager's National Provider Identifier (NPI) is 1669672739, a unique 10-digit ID issued by CMS for use in standard healthcare transactions.
- What is Justin Mager's specialty?
- Justin Mager is listed in the NPPES registry with a primary specialty of Internal Medicine Physician (Allopathic & Osteopathic Physicians).
- Where is Justin Mager located?
- Justin Mager's practice location on file with NPPES is 239 Miller Ave, Mill Valley, CA 94941-2841.
- What is Justin Mager's phone number?
- The practice phone number listed in the NPPES registry for Justin Mager is (415) 730-4235.
- Is Justin Mager's NPI active?
- Yes — Justin Mager's NPI (1669672739) is active in the NPPES registry as of the last update on 2012-11-05.
Source: CMS NPPES Data Dissemination (June 2026). NPI Central is not affiliated with CMS. Data is provided as-is from the public registry.