Definitions

Phase I: Clinical trials that generally last approximately one year and involve between 20 to 80 normal, healthy volunteers. The trials study a drug’s safety profile, including the safe dosage range. The studies also determine how a drug is absorbed, distributed, metabolized, and excreted and the duration of its action.

Phase II: Controlled studies of approximately 100 to 300 volunteers to assess the drug’s effectiveness. These studies take about two years.

Phase III: Studies last about three years and usually involve 1,000 to 3,000 volunteers. Volunteers are closely monitored to determine the effectiveness of a vaccine and identify adverse reactions.

Last Updated: 02/16/2007