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Useful Terms

Since clinical trials involve both medical and scientific practices and procedures, you may hear or read terms that are unfamiliar to you. Here is an explanation of many of the terms commonly used in clinical trials:

Adverse Event

An unfavorable change in the health of a participant, including abnormal laboratory findings, that happens during a clinical study or within a certain time period after the study is over. This change may or may not be caused by the intervention being studied.

Approved Drug

In the U.S., the Food and Drug Administration (FDA) must approve a substance as a drug before it can be marketed. The approval process involves several steps, including pre-clinical laboratory and animal studies, clinical trials for safety and efficacy, the filing of a New Drug Application by the manufacturer of the drug, FDA review of the application, and FDA approval/rejection of the application.

Blinding or Masking

This is the process through which one or more parties to a clinical trial is unaware of the treatment assignments. Blinded studies are conducted to prevent the unintentional biases that can affect subject data when treatment assignments are known. Types of blinding or masking include:

Single blind - A type of masking in which one party involved with the clinical trial, either the investigator or participant, does not know which participants have been assigned which interventions.

Double blind - A type of masking in which two or more parties involved with the clinical trial do not know which participants have been assigned which interventions. Typically, this includes the investigator and participant.

None/open label - Describes a clinical trial in which masking is not used. That means that all parties involved with the trial know which participants have been assigned which interventions. 

Cardiology/Vascular Diseases

These diseases involve the structure and function of the heart and blood vessels. Studies in these areas include: heart failure, coronary artery disease, high cholesterol, blood clots, circulation disorders and others.

Clinical Research

Medical research that involves people to test new treatments and therapies.

Clinical Study

A research study using human subjects to evaluate the effect of interventions or exposures on biomedical or health-related outcomes. Two types of clinical studies are interventional studies (or clinical trials) and observational studies.

Control Group

A comparison group of study subjects who are not treated with the investigational agent. The subjects in this group may receive no therapy, a different therapy or a placebo.

Drug Safety and Monitoring Board (DSMB)

An independent committee composed of community representatives and clinical research experts that reviews data while a clinical trial is in progress to ensure that participants are not exposed to undue risk. A DSMB may recommend that a trial be stopped if there are safety concerns or if the trial objectives have been achieved.

Effective Dose

This refers to a product's ability to produce beneficial effects for the duration or course of a disease. The effectiveness of the product is measured by evaluating the clinical and statistical results of clinical tests.

Eligibility Criteria

The key standards that people who want to participate in a clinical study must meet or the characteristics that they must have. These include inclusion criteria and exclusion criteria. For example, a study might only accept participants who are above or below certain ages. Inclusion criteria are the factors (or reasons) that allow a person to participate in a clinical study. Exclusion criteria are the factors (or reasons) that prevent a person from participating in a clinical study.

FDA (Food and Drug Administration)

The FDA is an agency within the U.S. Department of Health and Human Services. It is responsible for protecting the public health by making sure that human and veterinary drugs, vaccines and other biological products, medical devices, the nation's food supply, cosmetics, dietary supplements and products that give off radiation are safe, effective and secure.

Human Subjects Review Board

A group of people who review, approve, and monitor the clinical study protocol. Their role is to protect the rights and welfare of human research subjects participating in a study. The group typically includes people with varying backgrounds, including a community member, to make sure that research activities conducted by an organization are completely and adequately reviewed. This is also known as an institutional review board (IRB) or ethics committee.

IRB (Institutional Review Board)

An independent group of professionals designated to review and approve the clinical protocol, informed consent forms, study advertisements and patient brochures, to ensure that the study is safe and effective for human participation. It is also the IRB's responsibility to ensure that the study adheres to the FDA's regulations.

Inclusion/Exclusion Criteria

Factors that allow someone to participate in a clinical trial are called inclusion criteria. Those that exclude or not allow participation are called exclusion criteria.

Informed Consent

A process that explains risks and potential benefits about a clinical trial to a patient before they decide whether to participate. It is a process in which researchers communicate with potential and enrolled participants about a clinical study. This is when researchers: 
  1. Provide all the important information about the study, so that potential participants can decide whether to enroll (or if enrolled, to continue participating).
  2. Ensure that potential participants understand the risks and potential benefits of participating in the study, and the alternatives to the research being conducted. 
  3. Stress that enrolling in (and staying in) a clinical study is completely voluntary. Because giving consent to participate in research is not a contract, participants can leave a study at any time.
The goal of the informed consent process is to protect participants. It begins when a potential participant first asks for information about a study and continues throughout the study until the study ends. The researcher and potential participant have discussions that include answering the participant's questions about the research. All of the important information about the study must also be given to the potential participant in a written document that is clear and easy to understand. This informed consent document for a study is reviewed and approved by the Human Subjects Review Board before it is given to potential participants. Generally, a person must sign an informed consent document to enroll in a study.


This is a process or action that is the focus of a clinical study. It can include giving participants drugs, medical devices, procedures, vaccines and other products that are either investigational or already available. Interventions can also include noninvasive approaches such as surveys, education and interviews. An intervention type is the general category for the intervention being studied. Intervention types include drug, device, biological and procedure.

Interventional Study

This is a clinical study in which participants are assigned to receive one or more interventions (or no intervention) so that researchers can evaluate the effects of the interventions on biomedical or health-related outcomes. The assignments are determined by the study protocol. Participants may receive diagnostic, therapeutic or other types of interventions.

Investigational/Experimental Drug

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

Investigational Medical Device

A medical device that is the subject of a clinical study designed to evaluate the device’s effectiveness and/or safety.

Medical Device

This refers to any health care product that does not achieve its primary intended purposes by chemical action or being metabolized.

Observational Study

This is a clinical study in which participants identified as belonging to study groups are assessed for biomedical or health outcomes. Participants may receive diagnostic, therapeutic or other types of interventions, but the investigator does not assign participants to specific interventions (as in an interventional study). (This seems a little vague. Can we clarify it?)

Patient Volunteer

This is a patient who has a known health problem and participates in research to better understand, diagnose, treat or cure that disease or condition.

Phases of Clinical Trials

Clinical trials are conducted in “phases.” The trials at each phase have a different purpose and help researchers answer different questions.
  • Phase I Trials—An experimental drug or treatment is provided to a small group of people (20–80) for the first time. The purpose is to evaluate its safety and identify side effects.
  • Phase II Trials—The experimental drug or treatment is administered to a larger group of people (100–300) to determine its effectiveness and to further evaluate its safety.
  • Phase III Trials—The experimental drug or treatment is administered to even larger groups of people (1,000–3,000) to confirm its effectiveness, monitor side effects and compare it with standard or equivalent treatments.
  • Phase IV Trials—After a drug is licensed and approved by the FDA, researchers track its safety, seeking more information about its risks, benefits, and optimal use.


This is a pill or liquid that looks like the new treatment but does not have any treatment value from active ingredients.


A plan for the clinical trial that is carefully planned to safeguard the participants’ health and answer specific research questions.

Principal Investigator

This refers to a doctor who leads the clinical research team and, along with the other members of the research team, regularly monitors study participants’ health to determine the study’s safety and effectiveness. A principal investigator is responsible for the overall conduct of the clinical trial at his orher site.


The process by which two or more alternative treatments are assigned to volunteers by chance rather than by choice.

Serious Adverse Event

This is a medical event that results in death, is life-threatening, requires inpatient hospitalization or extends a current hospital stay, results in an ongoing or significant incapacity or interferes substantially with normal life functions, or causes a congenital anomaly or birth defect. Medical events that do not result in death, are not life-threatening, or do not require hospitalization may be considered serious adverse events if they put the participant in danger or require medical or surgical intervention to prevent one of the results listed above

Side Effect

A side effect is any undesired action or effect of a drug or treatment. Negative or adverse effects may include headache, nausea, hair loss, skin irritation or other physical problems. Experimental drugs must be evaluated for both immediate and long-term side effects.


This refers to the organization or person who oversees the clinical study and is responsible for analyzing the study data. A sponsor-investigator is the person who both initiates and conducts the clinical study. Sponsors can be government agencies such as the National Institutes of Health (NIH), pharmaceutical companies, individual doctors, health care centers and organizations that develop medical devices or equipment.

Standard of Care Treatment

This refers to the currently accepted treatment or intervention considered to be effective in the treatment of a specific disease or condition.

Types of Clinical Trials

The different types of clinical trials that are conducted include:
  • Diagnostic trials, which determine better tests or procedures for diagnosing a particular disease or condition. Diagnostic trials usually include people who have signs or symptoms of the disease or condition being studied.
  • Natural history studies, which provide valuable information about how disease and the patient’s health progress.
  • Prevention trials, which look for better ways to prevent a disease in people who have never had the disease or to prevent the disease from returning.
  • Quality of life trials (or supportive care trials), which explore and measure ways to improve the comfort and quality of life of people with a chronic illness.
  • Screening trials, which test the best way to detect certain diseases or health conditions.
  • Treatment trials, which test new treatments, new combinations of drugs or new approaches to surgery or radiation therapy. 

Vulnerable Subjects

This term refers to a group or individual that cannot give informed consent because of limited autonomy, for example, children, mentally ill patients and prisoners. This also refers to subjects who may be influenced to participate such as students, subordinates and patients.
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