Table 1.

Definition of clinical studies.

Phase	Definition
0	This phase, also called human micro-dosing studies, includes the administration of single sub-therapeutic doses of the studied drug to a small number of healthy subjects (10 to 15), to gather preliminary data on pharmacokinetics (PK).
1	This phase tests side effects, maximum tolerated dose and the dose-limiting toxicity, and drug formulation in a small number (20–100) of (often healthy) individuals.
2	This phase assesses the preliminary clinical safety and efficacy of selected doses in a dozen to a hundred patients with specific diseases.
3	This phase includes thousands of patients who have the disease or condition, to confirm clinical efficacy, effectiveness, and safety (confirmatory or pivotal studies).
4	Post-authorization safety studies, real world studies, and registries.