- Studies test the EFFICACY OF A DRUG OR DEVICE. LAST FROM SEVERAL MONTHS to TWO YEARS, and involves up to several hundred patients (100-300 PATIENT VOLUNTEERS) - RANDOMIZED TRIALS - 1 group of px receives the EXPERIMENTAL DRUG, while a 2nd "control" group receives standard treatment or PLACEBO. - studies are "BLINDED", neither the patients nor researchers know who has received the experimental drug. - allows investigators to provide the pharmaceutical company and the FDA with comparative information about the relative safety and effectiveness of the new drug. - intended to determine, BY ASCENDING DOSES, the multiple dose drug level required for a therapeutic response; clear recognition of the lower levels for adequate therapeutic response> > minimize ADR - EFFECTIVE DOSE be found by rapidly increasing the dosage within the parameters determined by the Phase I study. - evaluate STEADY-STATE MAINTENANCE LEVELS.