ClinicalTrials.gov MCP server

Search and read ClinicalTrials.gov studies, sites and outcomes. Hosted by usefulapi: connect it to Claude, ChatGPT, Cursor or any MCP client.

Connect ClinicalTrials.govFree 50 tool calls / monthPro $9/mo · $90/yr · pricing11 tools

What can I ask?

Turn on the ClinicalTrials.gov connector, then ask in plain words. The AI picks the tools.

Find recruiting trials for type 2 diabetes in Ohio.
How many trials are registered for migraine treatment?
Show me the full details and eligibility rules for trial NCT04280705.
What phase 3 trials for asthma are currently recruiting?

What you can do with ClinicalTrials.gov in Claude and ChatGPT

For researchers and health writers who look for studies on ClinicalTrials.gov.

Find trials for a condition, place and status

The AI searches the registry by condition, intervention, sponsor or location and filters by status or geography. You get a list of matching studies.

Read the full record of one trial by NCT ID

The AI fetches a study by its NCT id. It can return only chosen fields, so you can read eligibility rules or outcomes of that trial.

Count the trials that match a topic

The AI returns only the number of studies for a condition, intervention, sponsor, location or status. You see how big a research area is.

Sort trials by enrollment or latest update

The AI searches studies and sorts them, for example by enrollment count or last update date. It sums up the largest or most recently updated trials of a sponsor or condition.

Look up valid status and phase values for a search

The AI lists the values used in fields such as status or phase, and shows the study data model. You can then build a correct filter.

How do I connect ClinicalTrials.gov?

Before you connect

You do not need an account or a key for ClinicalTrials.gov. You log in with your email address and a 6-digit code.

ClinicalTrials.gov needs no credential.

Claude claude.ai · Desktop

Open Customize → Connectors, then click + Add → Add custom connector.
Enter the name ClinicalTrials.gov and this URL, then click Add:
https://clinicaltrialsgov.usefulapi.io/mcp
Claude opens the login page: enter your email and the 6-digit code from [email protected] (no ClinicalTrials.gov key needed).
In a chat, click + → Connectors and turn on ClinicalTrials.gov.

Team and Enterprise: an Owner adds the connector for the organization first.

ChatGPT chatgpt.com

Open Plugins, click +, then Add custom MCP server.
Enter the name ClinicalTrials.gov and this URL, choose OAuth as the authentication, confirm the warning and create it:
https://clinicaltrialsgov.usefulapi.io/mcp
ChatGPT opens the login page: enter your email and the 6-digit code from [email protected] (no ClinicalTrials.gov key needed).
In Plugins, install ClinicalTrials.gov, then choose it in a chat.

No Add custom MCP server option? It depends on your account or workspace settings: see OpenAI's guide.

Claude Code

Run this command, then run /mcp in Claude Code to log in:

claude mcp add --transport http clinicaltrialsgov https://clinicaltrialsgov.usefulapi.io/mcp

Cursor

Add to Cursor or add this to ~/.cursor/mcp.json:

{
  "mcpServers": {
    "clinicaltrialsgov": {
      "url": "https://clinicaltrialsgov.usefulapi.io/mcp"
    }
  }
}

VS Code

Add to VS Code or add this to .vscode/mcp.json:

{
  "servers": {
    "clinicaltrialsgov": {
      "type": "http",
      "url": "https://clinicaltrialsgov.usefulapi.io/mcp"
    }
  }
}

Codex

Run these commands. The second one opens the login page:

codex mcp add clinicaltrialsgov --url https://clinicaltrialsgov.usefulapi.io/mcp

codex mcp login clinicaltrialsgov

Other clients

Windsurf, Cline, Zed and other MCP clients: add this URL as a remote MCP server (Streamable HTTP). The client then opens the login page in your browser.

https://clinicaltrialsgov.usefulapi.io/mcp

Add only the URL. Do not add an Authorization header or an API key to the client config. The server signs you in with OAuth: the login page asks for your email address and a 6-digit code. If the config has such a header, remove it: some clients then send that header instead of the login token, and every call fails with 401.

Pricing

Plan	Price	Limit
Free	$0	50 tool calls / month
Pro	$9/mo · $90/yr	10,000 tool calls / month
Pro+	$39/mo · $390/yr	100,000 tool calls / month

Each paid plan covers this ClinicalTrials.gov server only. Ask your AI to run clinicaltrialsgov_upgrade and choose Pro or Pro+, billed monthly or yearly (it returns a Stripe Checkout link). If you already have Pro, ask to change it to Pro+. The change requires your confirmation, keeps your billing interval and charges the price difference for the rest of the period immediately. Cancel any time with clinicaltrialsgov_cancel_subscription: your paid plan continues to the end of the paid period, with no refund for the current period, and asking to resume the same plan with clinicaltrialsgov_upgrade before then undoes the cancel. Or write to [email protected].

Tools 11

Show all 11 tools (the AI picks them for you)

Read only · 7

Search clinical trials (ClinicalTrials.gov)clinicaltrialsgov_search_studies
Search the ClinicalTrials.gov v2 study registry. Provide any combination of query terms (condition, intervention, title, location, sponsor, general term) — multiple query.* terms are ANDed together — plus optional filters (status, geo, advanced Essie expression, explicit NCT ids). Returns { totalCount?, studies: [...], nextPageToken? }. Use `fields` to trim the response to specific fields/modules, `sort` to order (e.g. '@relevance', 'LastUpdatePostDate:desc', 'EnrollmentCount:desc'), and pageSize/pageToken to page.
Get a clinical trial by NCT IDclinicaltrialsgov_get_study
Fetch a single ClinicalTrials.gov study by its NCT id (format NCT######## — the letters 'NCT' followed by digits, e.g. NCT00841061). Returns the full study object { protocolSection, derivedSection?, hasResults? }. Use `fields` to return only specific fields/modules.
Count matching clinical trialsclinicaltrialsgov_count_studies
Return only the total NUMBER of studies matching a query, without fetching any records. Accepts the same query terms and filters as clinicaltrialsgov_search_studies (term, condition, intervention, title, location, sponsor, status, geoFilter, advanced). Returns { totalCount }. GET /studies with countTotal=true and pageSize=1.
List value statistics for study fieldsclinicaltrialsgov_list_field_values
Discover valid values / enums for one or more study fields. Returns per-field value statistics — for each field: its type, unique-value count and topValues [{value, studiesCount}]. Great for finding valid enum values (e.g. OverallStatus, Phase) before building a filter.
Get the study data-model (field tree)clinicaltrialsgov_get_study_metadata
Return the ClinicalTrials.gov study data model as a tree of module nodes (each with name/title/type/children). Use this to explore what fields/modules exist and their nesting, to build `fields` selections or `sort`/filter expressions.
Get study size statisticsclinicaltrialsgov_get_studies_stats
Return overall study-size statistics across the registry: { totalStudies, averageSizeBytes, percentiles, ranges, largestStudies }. Useful for understanding data volume.
Get the ClinicalTrials.gov API versionclinicaltrialsgov_get_api_version
Return the ClinicalTrials.gov API version and the timestamp of the underlying data snapshot: { apiVersion, dataTimestamp }.

Your usefulapi plan · 4

Usage status (free-tier meter)clinicaltrialsgov_usage_status
Report the caller's current usage: the plan, calls used this month, the limit of the plan (the free monthly cap or the Pro fair use limit), remaining, and whether the limit is reached. Read-only; does not count against the meter.
Request a missing featureclinicaltrialsgov_request_feature
Tell usefulapi that the user needs something the ClinicalTrials.gov tools cannot do yet (a missing tool, field or filter). Call it only when the user asks for something none of the tools can do, and tell the user that you send the request. Do not call it for errors or for normal requests. Do not include personal data, credentials or customer records. Stored with the product name and the client type (for example Claude or Cursor), without the user's account. At most 5 requests per day. Does not count against the meter.
Upgrade to Pro or Pro+clinicaltrialsgov_upgrade
Get a paid plan for ClinicalTrials.gov (the free tier caps monthly usage). Pro: 10,000 tool calls a month, for normal use — plan "monthly" ($9/month) or "yearly" ($90/year, 2 months free). Pro+: 100,000 tool calls a month, for automations and heavy use — plan "plus" ($39/month) or "plus_yearly" ($390/year). Without a plan it returns both Pro and Pro+, each with a payment link, for the user to choose; with a plan, one link. An existing Pro subscription changes to Pro+ in place (needs confirm: true; the price difference for the rest of the period is charged at once). Cancel any time: the plan then runs to the end of the paid period, so it also suits a one-time job. A link opens Stripe Checkout in the browser; after payment the account upgrades automatically. Does not count against the meter.
Cancel the Pro subscriptionclinicaltrialsgov_cancel_subscription
Cancel the caller's ClinicalTrials.gov Pro subscription at the end of the paid period (no refund for the current period; Pro continues until then, then the free tier applies). Requires confirm: true. Run clinicaltrialsgov_upgrade later to undo the cancel before the period ends. Does not count against the meter.

FAQ

What can I do with ClinicalTrials.gov in Claude or ChatGPT?

Find trials for a condition, place and status. Read the full record of one trial by NCT ID. Count the trials that match a topic. Sort trials by enrollment or latest update. Look up valid status and phase values for a search. See what you can do for the details.

Is this an official ClinicalTrials.gov product?

No. usefulapi is an independent service. It is not affiliated with or endorsed by ClinicalTrials.gov. The server calls the public ClinicalTrials.gov API for you.

Can I connect ClinicalTrials.gov to Claude or ChatGPT?

Yes. In Claude, add this server's URL as a custom connector. In ChatGPT, add it as a custom MCP server in Plugins. Then log in once. Cursor, VS Code, Claude Code and Codex work too. See the setup steps.

What do I need to connect?

Only an email address. You do not need a key for ClinicalTrials.gov.

Do I add an Authorization header to the client config?

No. Add only the URL. Do not add an Authorization header or an API key to the client config. The server signs you in with OAuth: the login page asks for your email address and a 6-digit code. If the config has such a header, remove it: some clients then send that header instead of the login token, and every call fails with 401.

Can the AI change my ClinicalTrials.gov data?

All 7 ClinicalTrials.gov tools are marked read-only.

What does it cost?

The Free plan gives 50 tool calls / month. Pro costs $9/mo or $90/yr, with 10,000 tool calls / month. Pro+ costs $39/mo or $390/yr, with 100,000 tool calls / month. Each subscription covers this ClinicalTrials.gov server only. Cancel any time: your paid plan then runs to the end of the paid period. Run clinicaltrialsgov_usage_status to see how many calls you used.

How do I subscribe or cancel?

Ask the AI to run clinicaltrialsgov_upgrade and choose Pro or Pro+, billed monthly or yearly: it returns a Stripe Checkout link. If you already have Pro, ask to change it to Pro+. After you confirm, your existing subscription changes in place, keeps its billing interval and charges the price difference for the rest of the period immediately. To cancel, run clinicaltrialsgov_cancel_subscription. Your paid plan continues to the end of the paid period.

What if a ClinicalTrials.gov tool that I need is missing?

Tell the AI what you wanted to do. It can send the request with clinicaltrialsgov_request_feature. We store the text with the server name, the type of AI client and the tool you tried, not with your account, and read every request when we plan new tools. You can send up to 5 requests per day.

Which AI clients can I use?

Any client that supports remote MCP servers (Streamable HTTP) with OAuth login: Claude (web and desktop), Claude Code, ChatGPT, Codex, Cursor, VS Code, Windsurf and others.

This is a Model Context Protocol endpoint — meant to be connected from an AI client, not opened in a browser. An invalid_token response at the URL is the auth gate working as designed; clients authenticate automatically.

Need a tool this server does not have, or a connection to another system? We build custom integrations and MCP servers.

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