What do the different phases of a clinical trial mean?

Clinical trials progress through several phases, each designed to answer specific research questions: 

• Phase 1: Involves a small group (20-80 participants), often healthy volunteers or patients with advanced diseases. The focus is on evaluating safety, identifying side effects, determining safe dosage ranges, and understanding how the body processes the investigational product. This phase typically lasts several months, with about 70% of studies advancing to Phase 2. 

• Phase 2: Enrols 100-300 participants with the condition under study to further assess safety and effectiveness. These trials may be randomised and controlled, comparing the investigational product to standard treatments or placebos. Blinding is often used to prevent bias. Phase 2 studies usually take up to two years, with approximately 33% progressing to Phase 3. 

• Phase 3: Includes larger groups (thousands of participants) to confirm effectiveness, monitor side effects, and compare the investigational product to standard treatments. These randomised and blinded trials can last from one to four years, with 25-30% successfully leading to regulatory approval submissions. 

• Phase 4: Conducted after regulatory approval, these post-marketing studies gather additional information on risks, benefits, and optimal use in various populations over extended periods. Findings can influence whether a product remains on the market or if usage guidelines need adjustments.