ChEMBL

Here's a little tip that may be of some use to you. The compound name search feature will also match substrings, so it is easy to type in a USAN/INN stem, and then retrieve all matching compounds - for example, "gliptin" will retrieve all DPP-IV inhibitors with non-proprietary (formal) names. This is pretty useful - of course the substring search functionality is not restricted to USANs/INNs.

A list of the current USAN stems is here. Note, they were never designed to be orthogonal, so the low complexity ones will give a lot of false positives.....