Clinical trials are a type of research study that investigates the safety and effectiveness of medical interventions on human health outcomes. Clinical trials are designed with specific objectives and protocols to gather scientific data on the intervention being tested. Before a clinical trial can begin, it undergoes a rigorous review process to ensure its scientific validity and ethical considerations.

Phase I: These studies are typically the first step in testing new drugs or treatments in humans. The primary focus is on assessing the drug's pharmacokinetics (how the body processes the drug) and pharmacodynamics (how the drug affects the body).

Phase II: It is conducted to evaluate its effectiveness in a larger group of patients and are designed to gather preliminary data on the treatment's efficacy for specific conditions and to guide further development.

Phase III: These studies involve thousands of participants and are typically carried out in multiple locations and countries. Phase III trials compare the new treatment against existing standard treatments or placebos to assess its safety, efficacy, and overall benefit-risk profile.

Phase IV: Once a drug or treatment receives regulatory approval and enters the market, phase IV trials, also known as post-marketing or observational studies, are conducted. These studies can provide valuable information on rare adverse effects, drug interactions, and outcomes in different patient populations.