• Phase 0 trial
  • Purpose: Exploratory phase with no therapeutic or diagnostic intent, aimed at gaining insight into pharmacokinetics and pharmacodynamics.
  • Only < ​1% of the therapeutic dose is used.
  • Safety and toxicity are not assessed.
  • Study population: Small sample consisting of either healthy individuals or a population with a disease of interest (∼ 10–15).
  • Study design: Open-label.
• Phase I trial
  • Purpose: Evaluation of pharmacodynamic and pharmacokinetic properties of the drug, safety, and toxicity.
  • Evaluation of the maximum tolerated dose.
  • Study population: Small number of healthy individuals or patients with a specific disease (∼ 15–30).
  • Study design: Open-label.
• Phase II trial
  • Purpose: Evaluation of efficacy, optimal dose range, and side effects (especially common and short-term side effects).
  • Study population: Moderate number of patients with a specific disease (∼ 10–100).
  • Study design: Randomized, Controlled, Anonymized.
• Phase III trial
  • Purpose: Final confirmation of safety and evaluation of efficacy against placebo or the current standard of care.
  • Study population: Randomized control trial with a large number of patients with a specific disease (∼ 100–1000).
  • Study design: Randomized Controlled Trial.
• Phase IV trial
  • Purpose: Postmarketing surveillance, comparing real-life efficacy to that described in research studies. Safety studies following approval (especially evaluation of rare and long-term side effects).
  • Study population: Large number of patients with a specific disease after drug approval.
  • Study design: Open-label.