Clinical Trial

What is a Clinical Trial?

A clinical trial is a study in people that evaluates a medical intervention, such as a drug, device, diagnostic tool, or treatment approach. It provides evidence about benefits and harms in the population studied. Conducting a trial does not, by itself, establish that the intervention is safe or effective.

Phases of Clinical Trials

These phases describe a common drug-development pathway. Other intervention types and study designs need not follow the same sequence.

• Phase I

  Phase I trials are the first stage of testing a new medical intervention in humans, typically involving a small group of healthy volunteers or people with the condition, depending on the intervention. Phase I examines safety, tolerability, dose, and pharmacokinetics: how the drug moves through and is processed by the body.

• Phase II

  Phase II trials involve a larger group of participants who have the condition that the intervention is intended to treat. The main objective of a Phase II trial is to further evaluate safety, as well as to assess the efficacy of the intervention and determine the optimal dose for further testing.

• Phase III

  Phase III trials are large-scale studies that enroll hundreds or thousands of participants, often at multiple sites. The primary aim of a Phase III trial is to establish the efficacy of the intervention in comparison to the current standard of care or a placebo, while continuing to monitor safety and any potential side effects. Positive results from a Phase III trial are typically required for regulatory approval.

• Phase IV

  Phase IV trials, also known as post-marketing surveillance studies, are conducted after a medical intervention has received regulatory approval and is available to the public. The purpose of a Phase IV trial is to monitor the intervention's long-term safety and effectiveness in a larger patient population, as well as to identify any rare or unexpected side effects that may not have been detected in earlier trial phases.

Key Components of Clinical Trials

• Informed Consent

  Before participating in a clinical trial, potential participants must provide informed consent, indicating that they understand the purpose of the study, the potential risks and benefits, and their rights as study participants. The consent process should give people the information and opportunity they need to decide whether to participate.

• Randomization

  Many clinical trials employ randomization, a process in which participants are randomly assigned to either the experimental group receiving the medical intervention or the control group receiving the standard of care or a placebo. Randomization helps minimize potential biases in the study and supports causal inference, but chance imbalance, attrition, nonadherence and other biases can still affect the result.

• Blinding

  Blinding, or masking, is a technique used in some clinical trials to prevent participants and researchers from knowing which group a participant has been assigned to. Masking can reduce biases caused by knowing the assigned treatment, including differences in expectations or outcome assessment. It does not guarantee an unbiased result.

Regulatory Oversight and Ethical Considerations

• Regulatory Authorities

  Clinical trials are subject to oversight by regulatory authorities, such as the U.S. Food and Drug Administration (FDA) or the European Medicines Agency (EMA), which are responsible for ensuring that clinical trials are conducted in accordance with established guidelines and regulations. Regulatory authorities also review the results of clinical trials to determine whether a medical intervention should be approved for use in the general population.

• Institutional Review Boards (IRBs)

  Institutional Review Boards (IRBs) or Ethics Committees are responsible for reviewing and approving the ethical aspects of clinical trials, including the study design, informed consent process, and measures to protect the safety and well-being of study participants. IRBs consist of experts from various disciplines, as well as community representatives, to ensure that the interests of both the scientific community and the public are considered.

• Adverse Event Reporting

  Throughout a clinical trial, researchers are required to monitor and report any adverse events or side effects experienced by participants. These reports help assess harms and inform decisions about continuing, changing, or stopping the study.

Sources and evidence

• U.S. Food and Drug Administration: Step 3: Clinical Research. Describes the usual phases of drug development.
• Sally Hopewell et al.: CONSORT 2025 explanation and elaboration: updated guideline for reporting randomised trials. Guidance for reporting randomized trials.