Accepts Healthy Volunteers
Indicates whether a clinical study allows people who do not have the condition, related conditions, or symptoms being studied to participate in that study.
Adverse Event (AE)
An unfavorable change in the health of a participant, including abnormal laboratory findings, that occur during a clinical study or within a certain time period after the study has ended. This change may or may not be caused by the intervention being studied.
A group or subgroup of participants in a clinical trial that receives specific interventions, or no intervention, according to the study protocol. This is decided before the trial begins.
A clinical trial design strategy in which one or more parties involved in the trial, such as the investigator or participants, do not know which participants have been assigned which interventions. Types of masking include Open Label, Single Blind Masking, and Double-Blind Masking.
Cardiovascular Disease
Also called heart disease is a class of diseases that involve the heart, the blood vessels (arteries, capillaries, and veins) or both.
Clinical Research/Clinical Trial
A medical research that involves people to test new treatments and therapies. Aims to advance medical knowledge, either through direct interaction or through the collection and analysis of blood, tissues, or other samples.
An online registry of clinical trials that are being conducted around the world. is operated by the National Library of Medicine at the National Institutes of Health and can be accessed by anyone.
Confidentiality Regarding Participants
The practice of maintaining all private information related to clinical trial participants, including their personal identity and all personal medical information. Results from the study will usually be presented in terms of trends or overall findings and will not mention any specific participants.
Control Group
The group of participants that receives standard treatment or a placebo. The control group may also be made up of healthy volunteers. Researchers compare results from the control group with results from the experimental group to find and learn from any differences.
Double-Blind Masking
A type of masking in which two or more parties involved in the clinical trial do not know which participants have been assigned which interventions. Typically, the parties include the investigator and participants.
Eligibility Criteria
The key standards or characteristics that people who want to participate in a clinical study must meet. Eligibility Criteria include both inclusion and exclusion criteria. For example, a study might only accept participants who are above or below certain ages.
Exclusion Criteria
The factors or reasons that prevent a person from participating in a clinical study.
A study done to answer a question. Other words to describe an experiment are research or study.
Experimental Group
The group of participants in a study that receive the experimental or study intervention.
Inclusion Criteria
The factors or reasons that allow a person to participate in a clinical study.
Informed Consent
A process used by researchers to communicate with potential and enrolled participants about a clinical study. Learn more about informed consent.
A person who is hospitalized for at least one night to receive treatment or participate in a study.
Institutional Review Board (IRB)
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 research activities conducted by an organization are adequately reviewed. Also known as an ethics committee.
A process or action that is the focus of a clinical study. Interventions include 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.
Investigational Drug
A drug being studied to see if your disease or medical condition improves while taking it. Can also be referred to as an experimental drug. Scientists may be studying the following aspect of the drug: If the drug is safe and effective. How the drug might be used in that disease. How much of the drug is needed. Information about the potential benefits and risks of taking the drug.
Interventional Study
A type of clinical study in which participants receive one or more interventions (or no intervention) so researchers can evaluate the outcomes. Participants may receive diagnostic, therapeutic, or other types of interventions.
Investigation New Drug (IND)
A drug or biological product that is used in a clinical trial, but has not been approved by the Food and Drug Administration (FDA). The drug is either not available for a doctor to prescribe or is available but has not been approved by FDA for the use being studied.
A researcher involved in a clinical study. Related terms include Site Principal Investigator, Site Sub-Investigator, Study Chair, Study Director, and Study Principal Investigator.
Minimal Risk
The probability and magnitude of harm or discomfort anticipated in the research are not greater than those ordinarily encountered in daily life or during the performance of routine physical or psychological examinations or tests.
National Institutes of Health (NIH)
The National Institutes of health (NIH) is part of the U.S. Department of Health and Human Services, is the nation's medical research agency — making important discoveries that improve health and save lives.
NCT Number
A unique identification code given to each clinical study registered on The format is "NCT" followed by an 8-digit number (for example, NCT00000419).
Observational Study
A type of 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).
Open Label
A clinical trial in which all parties involved in the trial know which participants have been assigned which interventions.
See our Frequently Asked Questions
A placebo is a pill or liquid that looks like the new treatment but does not have any treatment value from active ingredients.
Placebo Effect
When someone taking a medication receives benefits that are not from the chemicals in the medicine. Double-blind research design helps minimize the placebo effect.
Principal Investigator
The person who is responsible for the scientific and technical direction of the entire clinical study (for example, for all sites of a multisite study).
The written description of a clinical study. It includes the study's objectives, design, and methods. This may also include relevant scientific background and statistical information.
Randomization is the process by which two or more alternative treatments are assigned to volunteers by chance rather than by choice.
An organized system that uses observational study methods to collect uniform data (clinical and other) to evaluate specified outcomes for a population defined by a particular disease or condition.
Regulatory Agency
A public authority or government agency responsible for exercising autonomous authority over some area of human activity in a regulatory or supervisory capacity. Regulatory agencies deal in the area of administrative law—regulation or rulemaking (codifying and enforcing rules and regulations and imposing supervision or oversight for the benefit of the public at large).
A study done to answer a question. Scientists do research when they’re not sure what will work best to help people with an illness. Other words to describe clinical research are clinical trial, protocol, study, and experiment.
Serious Adverse Event (SAE)
An adverse 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.
Single Blind Masking
A type of masking in which one party involved in the clinical trial, either the investigator or participants, does not know which participants have been assigned which interventions.
Single-blind Research Design
A study in which one party, either the investigator or participant, is unaware of what medication or intervention the participant is taking; also called single-masked study.
Single- or Double-Blind Studies
Single- or double-blind studies (also called single- or double-masked studies) are studies in which the participants do not know which medicine is being used, so they can describe what happens without bias.
Clinical trials are sponsored or funded by various organizations or individuals, including physicians, foundations, medical institutions, voluntary groups, and pharmaceutical companies. Federal agencies such as NIH, FDA, the Department of Defense, and the Department of Veterans Affairs can also be a sponsor on a clinical trial.
Standard Treatment
The most prevalent and best available treatment at the time of the study.
Standardized Procedures
These are study rules that researchers must follow exactly for every participant, regardless of what each participant is used to.
Conducted by a principal investigator who is often a doctor. Members of the research team regularly monitor the participant’s health to determine the study’s safety and effectiveness. Other words to describe a study are clinical trial, protocol, experiment, and research.
Type of Clinical Trials
See our Frequently Asked Questions
U.S. Food and Drug Administration (FDA)
An agency within the U.S. Department of Health and Human Services. The FDA 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.

(Sources:, NIH, FDA)