RareTrial

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Clinical Trial
Glossary.

Every term you will encounter, explained without jargon.

A

Adverse Event

An unwanted symptom, injury, or health problem that occurs during a clinical trial. It may or may not be caused by the treatment. All adverse events must be reported to the study team, no matter how minor they seem.

Arm

A group of participants in a clinical trial who all receive the same treatment or intervention. Many trials have two or more arms - for example, one arm receives the new drug and another receives a placebo.

B

Blinding

When one or more parties involved in a trial do not know which treatment is being given. In a single-blind study, participants do not know. In a double-blind study, neither participants nor researchers know. Blinding prevents bias.

C

Clinical Trial

A research study conducted with people to evaluate a medical approach - such as a drug, device, diagnostic procedure, or behavioural change. Results from trials inform whether a treatment should be approved for wider use.

Cohort

A group of people who share a common characteristic and are studied over time. A cohort study follows a group to observe what happens to them.

Compassionate Use

Also called Expanded Access. A pathway that allows patients with serious or life-threatening conditions to access experimental treatments outside of a clinical trial, before they have received regulatory approval.

Control Group

The group in a clinical trial that does not receive the experimental treatment. They may receive a placebo, an existing standard treatment, or no treatment. The control group provides a comparison point.

D

Double-Blind

A study design where neither the participant nor the researchers know who is receiving the experimental treatment and who is receiving the control. This is one of the strongest methods for eliminating bias.

E

Eligibility Criteria

The specific requirements a person must meet to participate in a clinical trial. Inclusion criteria define who qualifies. Exclusion criteria define who is ruled out. These exist to protect safety and ensure reliable results.

Endpoint

A measurable outcome that researchers track to determine whether a treatment is working. The primary endpoint is the most important measure. Secondary endpoints provide additional information.

Expanded Access

A pathway that allows patients with serious or life-threatening diseases to access investigational drugs or devices outside of a clinical trial. Also called compassionate use. Requires approval from the FDA and the drug manufacturer.

F

FDA

The US Food and Drug Administration. The federal agency responsible for approving drugs, medical devices, and biological products in the United States. A drug must be proven safe and effective in clinical trials before the FDA will approve it.

I

Informed Consent

The process of explaining a clinical trial to a potential participant before they agree to join. The researcher must explain the purpose, procedures, risks, benefits, and alternatives. You can withdraw consent at any time and for any reason.

Institutional Review Board (IRB)

An independent committee - also called an Ethics Committee - that reviews and approves clinical trial protocols before the study begins. The IRB exists to protect the rights, safety, and wellbeing of research participants.

Intervention

The treatment, drug, device, or procedure being tested in a clinical trial. An interventional study tests a specific intervention. An observational study watches participants without intervening.

Investigational Drug

A drug that has not yet been approved by the FDA for general use. Also called an experimental drug or study drug. Clinical trials test investigational drugs to determine whether they are safe and effective.

N

NCT Number

The unique identification code assigned to every study registered on ClinicalTrials.gov. NCT stands for National Clinical Trial. Always starts with "NCT" followed by 8 digits (e.g., NCT01234567). Use this number to look up a specific trial.

O

Open-Label

A study design where both the participant and the researcher know what treatment is being administered. The opposite of blinded. Often used in Phase 1 trials, or in extension studies after a blinded period ends.

Orphan Drug

A drug developed specifically to treat a rare disease (one affecting fewer than 200,000 people in the US). The FDA offers incentives for orphan drug development, including faster review and market exclusivity.

Outcome Measure

A specific measurement used to evaluate whether a treatment is having an effect. Examples include survival time, quality of life scores, lab values, or physical function tests.

P

Phase 1

The first stage of testing a new treatment in humans. Usually involves 20-80 people. The main goal is to assess safety, determine a safe dose range, and identify side effects. Participants are sometimes healthy volunteers.

Phase 2

Tests whether the treatment actually works and continues to assess safety. Usually involves 100-300 people who have the disease being studied. Researchers look for evidence of effectiveness and monitor side effects more closely.

Phase 3

Large-scale testing comparing the new treatment to existing treatments or a placebo. Usually involves 1,000-3,000 people across multiple study sites. FDA approval requires at least one successful Phase 3 trial.

Phase 4

Studies conducted after a treatment has been approved by the FDA. Also called post-market surveillance. These trials monitor long-term safety, effectiveness in broader populations, and new uses of the approved treatment.

Placebo

An inactive substance (like a sugar pill or saline injection) that looks identical to the real treatment. Placebos are used in control groups to allow an unbiased comparison. Receiving a placebo does not mean you receive no care.

Principal Investigator

The lead researcher responsible for a clinical trial at a specific study site. Abbreviated PI. The PI is responsible for following the study protocol and protecting participants at their site.

Protocol

The detailed written plan for a clinical trial. It describes the purpose, design, methods, eligibility criteria, outcome measures, and statistical analysis plan. All participating sites must follow the same protocol.

R

Randomization

The random assignment of participants to different treatment groups. Like flipping a coin. Randomization helps ensure that the groups are similar and that any difference in outcomes is due to the treatment, not other factors.

Rare Disease

In the United States, a disease affecting fewer than 200,000 people. In the European Union, fewer than 1 in 2,000 people. Also called an orphan disease. There are an estimated 7,000 rare diseases, affecting 300 million people worldwide.

S

Screening

The process of checking whether a potential participant qualifies for a trial. Includes medical tests, questionnaires, and interviews. Screening does not guarantee enrollment. Some people who pass screening are still not enrolled due to study capacity.

Serious Adverse Event (SAE)

A medical problem during a trial that is life-threatening, results in death, causes hospitalisation, leads to permanent disability, or results in a birth defect. SAEs must be reported to the IRB and the FDA.

Sponsor

The organization or individual that initiates, manages, and finances a clinical trial. Sponsors are often pharmaceutical companies, biotech firms, government agencies (like the NIH), or academic institutions.

Study Coordinator

The person at a study site who manages day-to-day operations: scheduling visits, collecting data, communicating with participants, and tracking eligibility. Usually your main point of contact at a trial site.