Phase 1 studies are usually designed with an emphasis on the assessment of safety and tolerability of an investigational drug in a small group of people for the first time. It can include healthy participants or participants with the disease.

Phase 2 studies are usually designed to begin to evaluate the efficacy of an investigational drug in a higher number of participants with the disease, and often used to obtain dose-ranging information. Safety also continues to be assessed during this phase.

Phase 3 studies are designed to confirm the data of Phase 2 studies for an investigational drug. Large numbers of participants with the disease are generally involved to obtain safety and efficacy data to evaluate the overall benefit-risk relationship of an investigational drug to provide an adequate basis for regulatory approvals. Given the size of these studies and to ensure a representative sample of patients, they are often conducted across several countries.