Phase I, II, III, or IV study

A codification system for the various phases of clinical trials of new technologies.

Note: The system applies mainly to drugs and devices. These trials are part of the development and approval process required by regulatory agencies.

Phase I trial:
A trial usually involving 20 to 80 healthy volunteers to determine a drug’s safety, safe dosage range, absorption, metabolic activity, excretion and duration of activity.

Phase II trial:
A controlled trial involving 100 to 300 subjects to determine a drug’s efficacy and adverse reactions to the drug (these trials are sometimes divided into Phase IIa pilot trials and Phase IIb well-controlled trials).

Phase III trial:
A large controlled trial to determine a drug’s efficacy and monitor adverse events during longer-term use (these trials are sometimes divided into Phase IIIa trials, conducted before the marketing authorization application, and Phase IIIb trials, conducted after the marketing authorization application, but before approval).

Phase IV trial:
A post-marketing pharmacovigilance study to monitor a drug’s long-term effects and provide additional information on the drug’s safety and efficacy, including for patient groups with different dosing regimens.