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UMLS REST API

National Library of Medicine · Health

Health API Key Free & Open Healthcare Life Sciences UMLS Medical Terminology SNOMED

Unified Medical Language System (UMLS) REST API from NIH/NLM. Cross-vocabulary concept lookups spanning ICD-10, SNOMED CT, LOINC, RxNorm, CPT, and 200+ biomedical vocabularies. Essential for medical terminology mapping and interoperability.

Authentication

API Key API key from UMLS license — register free at https://uts.nlm.nih.gov/uts/signup-login. Pass as ?apiKey= query parameter.

Sample Requests

GET Search UMLS concepts

Search across all UMLS vocabularies for a medical concept

https://uts-ws.nlm.nih.gov/rest?apiKey={your_api_key}&string=diabetes mellitus&searchType=words

Hover any highlighted part to learn what it does

curl -X GET "https://uts-ws.nlm.nih.gov/rest?apiKey=%7Byour_api_key%7D&string=diabetes%20mellitus&searchType=words"
import requests
params = {
    "apiKey": "{your_api_key}",
    "string": "diabetes mellitus",
    "searchType": "words"
}
response = requests.get(
    "https://uts-ws.nlm.nih.gov/rest",
    params=params,
)
print(response.json())
const url = new URL('https://uts-ws.nlm.nih.gov/rest');
url.searchParams.set('apiKey', '{your_api_key}');
url.searchParams.set('string', 'diabetes mellitus');
url.searchParams.set('searchType', 'words');

const response = await fetch(url); 
const data = await response.json();
console.log(data);
package main

import (
	"fmt"
	"io"
	"net/http"
	"net/url"
)

func main() {
	baseURL, _ := url.Parse("https://uts-ws.nlm.nih.gov/rest")
	q := baseURL.Query()
	q.Set("apiKey", "{your_api_key}")
	q.Set("string", "diabetes mellitus")
	q.Set("searchType", "words")
	baseURL.RawQuery = q.Encode()
	targetURL := baseURL.String()
	req, _ := http.NewRequest("GET", targetURL, nil)

	client := &http.Client{}
	resp, _ := client.Do(req)
	defer resp.Body.Close()
	body, _ := io.ReadAll(resp.Body)
	fmt.Println(string(body))
}
require "net/http"
require "json"

uri = URI("https://uts-ws.nlm.nih.gov/rest")
uri.query = URI.encode_www_form({
  "apiKey" => "{your_api_key}",
  "string" => "diabetes mellitus",
  "searchType" => "words"
})

http = Net::HTTP.new(uri.host, uri.port)
http.use_ssl = uri.scheme == "https"

req = Net::HTTP::Get.new(uri)

res = http.request(req)
puts JSON.parse(res.body)
<?php
$url = "https://uts-ws.nlm.nih.gov/rest?" . http_build_query([
    "apiKey" => "{your_api_key}",
    "string" => "diabetes mellitus",
    "searchType" => "words"
]);
$opts = ["http" => [
    "method" => "GET",
]];
$ctx = stream_context_create($opts);
$res = file_get_contents($url, false, $ctx);
print_r(json_decode($res, true));

Postman Setup Guide

Get Postman ↗
  1. Register free at https://uts.nlm.nih.gov/uts/signup-login for a UMLS license and API key
  2. In Postman, GET https://uts-ws.nlm.nih.gov/rest/search/current
  3. Add params: string={term}, apiKey={your_key}, searchType=words
  4. Results return CUI (concept identifier) and source vocabularies
  5. Use CUI to fetch concept details: GET /rest/content/current/CUI/{cui}

What can you build with UMLS REST API?

UMLS REST API is a Health API. Developers commonly use health APIs for:

  • accessing medical reference data and drug information
  • building patient-facing health tracking apps
  • integrating with EHR and telemedicine platforms
  • looking up ICD codes and clinical terminology
  • powering wellness and fitness applications

API Key authentication. You'll receive a key after signing up. Send it with every request — in a header or query parameter. Keep it out of client-side code and never commit it to version control. UMLS REST API is free to use, making it a low-risk choice to experiment with.

New to APIs? Read our beginner's guide · Learn about API keys · What is REST?

Open documentation ↗