Clinical Trial Glossary
Clinical trials use specialized language that can be confusing. This glossary defines 30 key terms in plain English — so patients, caregivers, and advocates can understand the research process.
Trial Phases
Phase 1 Trial
The first stage of testing a new treatment in humans, focused primarily on safety, dosing, and side effects in a small group of volunteers.
Phase 2 Trial
The second stage of testing, which evaluates whether the treatment works for its intended condition and continues to assess safety in a larger group.
Phase 3 Trial
A large-scale study that confirms effectiveness, monitors side effects, and compares the new treatment to existing options — the final step before seeking regulatory approval.
Phase 4 Trial (Post-Marketing)
Studies conducted after a drug has been approved and is on the market, monitoring long-term safety, effectiveness in broader populations, and rare side effects.
Study Design
Randomized Controlled Trial (RCT)
A study design where participants are randomly assigned to receive either the experimental treatment or a control (placebo or standard therapy), considered the gold standard in clinical research.
Double-Blind Study
A study design where neither the participants nor the researchers know who is receiving the treatment and who is receiving the placebo, minimizing bias in results.
Placebo
An inactive substance or treatment (such as a sugar pill) given to the control group in a clinical trial, designed to look identical to the active treatment being tested.
Placebo-Controlled Trial
A clinical trial that includes a placebo group to compare against the experimental treatment, helping researchers determine whether the treatment has a real effect.
Crossover Study
A clinical trial design where each participant receives both the treatment and the control at different times, serving as their own comparison.
Open-Label Study
A clinical trial in which both the participants and the researchers know which treatment each participant is receiving — there is no blinding.
Participants & Eligibility
Informed Consent
The process by which a potential participant learns the key facts about a clinical trial — including risks, benefits, and alternatives — before deciding whether to enroll.
Inclusion Criteria
The specific characteristics that a person must have to be eligible for a clinical trial, such as age range, diagnosis, or stage of disease.
Exclusion Criteria
The characteristics that disqualify a person from participating in a clinical trial, such as certain medical conditions, medications, or pregnancy.
Regulation & Oversight
Data Safety Monitoring Board (DSMB)
An independent committee of experts that monitors the safety data from a clinical trial while it is ongoing, with the authority to recommend stopping the trial if needed.
Institutional Review Board (IRB)
An independent ethics committee that reviews and approves clinical research involving human subjects to ensure participants' rights, safety, and welfare are protected.
FDA Approval Process
The regulatory pathway through which the U.S. Food and Drug Administration evaluates and approves new drugs, biologics, and medical devices for public use.
Investigational New Drug (IND)
An application submitted to the FDA before a new drug can be tested in humans, containing preclinical data demonstrating safety and a plan for clinical trials.
New Drug Application (NDA)
The formal application submitted to the FDA after clinical trials are complete, requesting approval to market a new drug for sale in the United States.
Biologics License Application (BLA)
The regulatory application submitted to the FDA for approval of biological products such as vaccines, gene therapies, and monoclonal antibodies.
ClinicalTrials.gov
The world's largest public database of clinical studies, maintained by the U.S. National Library of Medicine, where researchers are required to register their trials.
Outcomes & Analysis
Adverse Event (AE)
Any undesirable medical occurrence in a clinical trial participant, whether or not it is caused by the treatment being studied.
Serious Adverse Event (SAE)
An adverse event that results in death, hospitalization, disability, a life-threatening situation, or a birth defect — requiring immediate reporting to regulators.
Primary Endpoint
The main outcome measure that a clinical trial is designed to evaluate — the specific result that determines whether the treatment is considered effective.
Secondary Endpoint
Additional outcome measures in a clinical trial that provide supporting evidence about the treatment's effects, safety, or quality-of-life impact.
Statistical Significance
A mathematical determination that the observed results of a clinical trial are unlikely to have occurred by chance, typically defined as a p-value less than 0.05.
Intention-to-Treat (ITT) Analysis
A statistical approach that includes all participants in the analysis based on their original group assignment, regardless of whether they completed the treatment.
Per-Protocol Analysis
A statistical approach that only includes participants who completed the trial exactly as designed, without major protocol deviations.
Study Types
Clinical Trial
A research study that tests a medical treatment, drug, device, or intervention in human volunteers to determine whether it is safe and effective.
Compassionate Use
A pathway that allows seriously ill patients to access experimental treatments outside of clinical trials when no other options exist.
Expanded Access
A program that provides an investigational drug to a group of patients with serious conditions outside of a clinical trial, often while the drug is being reviewed for approval.