MedlinePlus MCP

Open-source Model Context Protocol server for MedlinePlus Connect, the U.S. National Library of Medicine service for linking clinical codes and medication names to patient-friendly health information.

This server gives an AI agent narrow tools for looking up public MedlinePlus education links. It is intentionally not a medical-record server and does not store patient data.

Why

Agents working near health records need trustworthy reference material, but they should not invent medication side effects, lab explanations, or condition summaries from memory.

medlineplus-mcp keeps the privacy boundary simple:

• Send generic lookup terms or codes to MedlinePlus, such as metformin, an RXCUI, an NDC, a LOINC code, an ICD-10-CM code, a CPT code, or a SNOMED CT code.
• Keep private chart context local in your own agent or application.
• Merge public education links with private patient context only after the lookup result comes back.

Tools

lookup_medication

Look up medication education links using:

• name: English medication name fallback, such as metformin
• rxcui: RxNorm Concept Unique Identifier
• ndc: National Drug Code
• language: en or es

Spanish medication responses generally require RXCUI or NDC.

lookup_diagnosis

Look up diagnosis/problem education links using:

• code: ICD-10-CM, ICD-9-CM, or SNOMED CT code
• codeSystem: icd10cm, icd9cm, or snomedct
• name: optional display name
• language: en or es

lookup_lab_test

Look up lab-test education links using:

• loinc: LOINC code
• name: optional display name
• language: en or es

lookup_procedure

Look up procedure education links using:

• code: CPT or SNOMED CT code
• codeSystem: cpt or snomedct
• name: optional display name
• language: en or es

medlineplus_connect

Low-level escape hatch for supported MedlinePlus Connect request types.

Install

git clone https://github.com/chrisvo/medlineplus-mcp.git
cd medlineplus-mcp
npm install
npm test

Run

npm start

Example MCP config:

{
  "mcpServers": {
    "medlineplus": {
      "command": "node",
      "args": ["/absolute/path/to/medlineplus-mcp/src/server.mjs"],
      "cwd": "/absolute/path/to/medlineplus-mcp",
      "env": {
        "MEDLINEPLUS_CACHE_TTL_MS": "43200000"
      }
    }
  }
}

MEDLINEPLUS_CACHE_TTL_MS defaults to 12 hours. MEDLINEPLUS_CACHE_DIR defaults to .cache/medlineplus-mcp; set it to off to disable persistent disk caching.

Caching

The server uses two cache layers:

• in-memory cache for repeated lookups during the current process,
• filesystem cache so repeated lookups survive process restarts.

By default cache files are written under .cache/medlineplus-mcp/ in the server working directory. Cache keys are SHA-256 hashes of the MedlinePlus Connect request URL, and cached payloads contain only the public response from MedlinePlus plus the generic lookup request.

For a different cache folder:

MEDLINEPLUS_CACHE_DIR=/var/cache/medlineplus-mcp npm start

To disable disk caching:

MEDLINEPLUS_CACHE_DIR=off npm start

Output

Tool responses are JSON text payloads:

{
  "request": {
    "type": "drug",
    "codeSystem": "ndc",
    "code": "",
    "name": "metformin",
    "language": "en"
  },
  "query_url": "https://connect.medlineplus.gov/service?...",
  "attribution": "U.S. National Library of Medicine",
  "updated": "2026-07-18T03:05:36Z",
  "total_results": 1,
  "entries": [
    {
      "title": "Metformin",
      "url": "https://medlineplus.gov/druginfo/meds/a696005.html",
      "summary": "",
      "source": "American Society of Health-System Pharmacists, Inc."
    }
  ]
}

Privacy

Do not send private chart notes, diagnoses, full medication administration records, names, MRNs, dates of birth, or free-form patient narratives to this server unless you are intentionally sending them to MedlinePlus Connect.

Prefer generic lookups:

• Good: metformin
• Good: rivaroxaban
• Good: 4548-4 for a LOINC lookup
• Bad: an entire hospital progress note

Acceptable Use

MedlinePlus says Connect requests should stay under 100 requests per minute per IP address and recommends caching results for 12-24 hours. This server includes in-memory and disk caching by request URL.

See the official docs:

• MedlinePlus Connect
• MedlinePlus Connect Web Service
• Technical Information
• MedlinePlus for Developers

Medical Safety

MedlinePlus content is patient education, not a clinical decision engine. Agents using this MCP should:

• cite returned MedlinePlus links,
• separate public general education from patient-specific interpretation,
• avoid telling users to stop, start, or change medications,
• suggest questions for the care team when private clinical context matters.

License

MIT