Why am I getting a HTTP status code of 301 when I do an API request?

Starting April 18, 2016 the API servers are redirecting any http: requests to https. If you are making an API request using http, you should change it to https to avoid this status returned.

Do I need a license to run the RxNorm/RxTerms/Prescribable/RxClass API?

With one exception, no license is needed to use any of the above APIs. The only exception is the /rxcui/{rxcui}/proprietary function in the RxNorm API, which requires the user to have a valid UMLS license and pass a proxy granting ticket as a parameter to the function.

Is there a limit to the number of API calls I can make?

Yes, to accomodate the increasing usage and many users of the APIs, there is a limit on the number of API calls a user can make in a given time period. Consult the Terms of Service for more details.

How will I know if I exceed the terms of service limit?

If the API call limit is exceeded, then the servers will return an HTTP status code of 429 ("Too many requests").

Do the APIs allow Cross-origin resource sharing (CORS)?

Yes

Does RxNav offer information about drug/drug interactions?

RxNav's drug/drug interaction features were discontinued on January 2, 2024. However, the sources from which RxNav drew may remain available. Those sources were: (1) "High-priority drug–drug interactions for use in electronic health records", supplemented using CredibleMeds' list of drugs that have a known risk of Torsades de Pointes (TdP); and (2) DrugBank's drug/drug interaction dataset.