Medical reference data and statistics by Public Health Scotland.
Open Data NHS Scotland API is a free Health API that requires no API key, is served over HTTPS and has unconfirmed CORS support.
Details from opendata.nhs.scot.

Unified API suite · now live
Geocode an address, validate an email, track a flight or pull stock data with one account, one dashboard and one API key.
Public FDA data about drugs, devices and foods
The Open Data NHS Scotland API is provided by Scottish Health and Social Care Open Data (opendata.nhs.scot).
Yes. The Open Data NHS Scotland 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.
No. The Open Data NHS Scotland API requires no authentication, so you can start making requests without signing up.
CORS support for the Open Data NHS Scotland API is unknown. Test a request from the browser, and fall back to a server-side call if it is blocked.
Yes. The Open Data NHS Scotland API is served over HTTPS, so it's safe to use in production.