The first in a series of studies each drug goes through before reaching the public. Phase 1 trials involve a small number of subjects (either patients or healthy participants depending on the trial), and seek to determine the metabolism and pharmacologic actions of drugs in humans, as well as any side-effects. Subjects are recruited slowly, beginning with very small dosages, with the dosage and number of subjects building over a period of time

See also:
Phase II trials
Phase III trials
Phase IV trials
Clinical trial
Clinical trial enrolment
Pre-clinical trials