NHS conditions, medicines and guidance.
NHS Health A-Z API is a free Health API that requires apiKey authentication, is served over HTTPS and has unconfirmed CORS support.

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Makeup Information
Yes. The NHS Health A-Z API is listed in the Health category of the public-apis directory, which only includes APIs that are free or have a free tier. Check its documentation for rate limits and paid plans.
Yes. The NHS Health A-Z API uses apiKey authentication, so you need to register for credentials before making requests.
CORS support for the NHS Health A-Z API is unknown. Test a request from the browser, and fall back to a server-side call if it is blocked.
Yes. The NHS Health A-Z API is served over HTTPS, so it's safe to use in production.