Type 1 · Individual ✓ Active NPI ✓ Valid NPI checksum

Alexander Thomas O'Brien, PMHNP

Psychiatric/Mental Health Nurse Practitioner in Chestnut Hill, MA · enumerated 2021.

Data current as of Jul 13, 2026 · sourced from CMS NPPES

National Provider Identifier

1598420770

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Registry record

Entity type Individual (Type 1)

Name Alexander Thomas O'Brien

Credential PMHNP

Sex Male

Practice address 300 South St, Chestnut Hill, MA, 02467

Phone (617) 469-0300

Enumeration date Nov 3, 2021

Last updated in NPPES Mar 13, 2023

Taxonomy & licenses

363LP0808X Psychiatric/Mental Health Nurse Practitioner Physician Assistants & Advanced Practice Nursing Providers · License 234518 (MA) Primary

What is an NPI number?

A National Provider Identifier (NPI) is a unique 10-digit number that CMS assigns to every U.S. healthcare provider and organization under HIPAA. Type 1 NPIs identify individual providers; Type 2 NPIs identify organizations. The NPI appears on insurance claims, prescriptions, and credentialing paperwork, and never changes, even if the provider moves or changes specialty.

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Frequently asked questions

What specialty is Alexander O'Brien?

Alexander O'Brien is registered in NPPES with the primary taxonomy of Psychiatric/Mental Health Nurse Practitioner. The taxonomy code describes the provider's classification and area of specialization for claims and credentialing.

Is this the official NPI registry?

No. NPI Portal is a private site built on public CMS NPPES data. The official registry is npiregistry.cms.hhs.gov, operated by CMS.

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Source: CMS NPPES (public data). Snapshot 2026-07-13. Provider record last updated 2023-03-13.