passed an amendment, expressly granting FDA authority to consider other types of confirmatory evidence along with one adequate and well-controlled clinical investigation for approval.

The trials are typically conducted in three phases:
* Phase 1: The drug is tested in 20 to 100 healthy volunteers to determine its safety at low doses. About 70% of candidate drugs advance to Phase 2.
* Phase 2: The drug is tested for both efficacy and safety in up to several hundred people with the targeted disease. Some two-thirds of candidate