Active, not recruiting

The clinical trial is happening, but researchers are not looking for more participants at this time.

Adverse event

A medical problem that happens or worsens during a clinical trial or within a certain time period after the trial is over. An adverse event may or may not be caused by the investigational treatment a person took.

Clinical trial (or research study)

A clinical trial is a research study designed to learn how our bodies respond to investigational medicines or other investigational treatments. During the clinical trial, participants are assigned to get a treatment or sometimes, no treatment. The purpose of a trial is usually to find ways to prevent, diagnose, or treat a disease or other health condition.

Clinical trial phases

Any treatment (vaccine, medicine, medical device, or procedure) must go through 4 phases of clinical trials. Each phase tests the treatment’s safety, how well it works, amount (dose), and side effects.


A disease, disorder, syndrome, illness, or injury that researchers are studying.

Controlled trial

A type of clinical trial that compares one treatment to another treatment. Often, a new investigational treatment is compared to a standard or usual treatment (called the control). The control may be a group of participants in the same trial or a group of participants from an earlier trial or study.

Eligibility criteria

A clinical trial’s requirements for people who want to join. These include inclusion criteria (factors that allow a person to join a trial) and exclusion criteria (factors that prevent a person from joining a trial). For example, a trial might only accept participants who are above or below certain ages.


The number of participants in a clinical trial. The “estimated enrollment” is the number of participants that the researchers need for the trial.

Exclusion criteria

The factors (or reasons) that prevent a person from joining a clinical trial.

Expanded access

A process regulated by the federal agencies that allows pharmaceutical companies to provide a new investigational treatment (before it’s approved) to patients with serious diseases or conditions who cannot take part in a clinical trial.

Inclusion criteria

The factors (or reasons) that allow a person to join a clinical trial.

Informed consent

Informed consent is the process in which researchers talk with people who are thinking about enrolling, or have enrolled, in a clinical trial. They will have you read an informed consent form (ICF) that describes the possible benefits and risks. It tells you that taking part in the trial is voluntary, and that you may leave the trial at any time.

The goal of the informed consent process is to protect the participants who enroll in clinical trials. The informed consent process starts when a possible participant first asks for information about a trial and continues until the trial ends.

Informed consent form (ICF)

The document used in the informed consent process.

Investigational medication

A drug or biological product that is used in a clinical trial but has not been approved by health authorities (the drug is either not available for a doctor to prescribe or is available but not approved by the health authority for the use being studied).

Institutional Review Board (IRB)

A committee of doctors, data experts, community advocates, and others who help ensure that a trial is done in an ethical manner and the rights of participants are protected. They review, approve, and check on the trial’s plan (protocol) that explains what researchers will do during the trial. For example, they will review the informed consent form. Also called an ethics committee.

Open studies

Studies that are enrolling participants now or in the future, or involve drugs that are available for expanded access (may be used by certain patients before federal agency approval).


A look-alike substance that does not contain an active drug or treatment. A placebo is made to look, taste, and be given like the actual drug being studied.


The written description of a clinical trial. It includes the trial’s goals, design, and methods. It may also include data and science-related background information.


The organization or person who starts the trial, pays for it, and has authority and control over it.


A treatment that helps provide protection to certain infections, usually given as a shot.

Still have questions?

Our FAQ section has answers to commonly asked questions and a glossary of words to know.


Frequently asked questions

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