Heard in television ads for cancer treatment centers, the phrase investigational drugs. From an FDA site on “Access to Investigational Drugs”:
Investigational or experimental drugs are new drugs that have not yet been approved by the FDA or approved drugs that have not yet been approved for a new use, and are in the process of being tested for safety and effectiveness.
This passage treats investigational and experimental as synonyms in the drug context — but then the site goes on to use investigational exclusively. This specialized use of investigational (as opposed to the transparent general use ‘of or relating to investigations’) seems to be fairly recent — recent enough that it’s not in the dictionaries I’ve consulted. It seems to have replaced experimental as the appropriate technical term for drugs undergoing testing, perhaps because some people in the relevant community had come to feel that experimental no longer sounded sufficiently technical, but had become part of ordinary language.
