Skip Navigation and Go To Content


The following glossary defines the most commonly used terms used in clinical trials

A-C      D-F      G-I      J-N      O-Q      R-Z 

Adverse reaction(Adverse Event.) An unwanted effect caused by the administration of drugs. Onset may be sudden or develop over time (See Side effects).

Advocacy and support groups 
Organizations and groups that actively support participants and their families with valuable resources, including self-empowerment and survival tools. 

Approved drugs 
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, filing of a New Drug Application by the manufacturer of the drug, FDA review of the application, and FDA approval/rejection of application (See Food and Drug Administration

Arm Any of the treatment groups in a randomized trial. Most randomized trials have two "arms," but some have three "arms," or even more. (See Randomized trial). 
Back to top

1) Information gathered at the beginning of a study from which variations found in the study are measured. 2) A known value or quantity with which an unknown is compared when measured or assessed. 3) The initial time point in a clinical trial, just before a participant starts to receive the experimental treatment which is being tested. At this reference point, measurable values such as CD4 count are recorded. Safety and efficacy of a drug are often determined by monitoring changes from the baseline values.

Bias  When a point of view prevents impartial judgment on issues relating to the subject of that point of view. In clinical studies, bias is controlled by blinding and randomization (See Randomization).

Blind  A randomized trial is "blind" if the participant is not told which arm of the trial he is on. A clinical trial is "blind" if participants are unaware on whether they are in the experimental or control arm of the study. (See Single-blind study andDouble-blind study). 
Back to top

Clinical  Pertaining to or founded on observation and treatment of participants, as distinguished from theoretical or basic science. 

Clinical endpoint  See Endpoint

Clinical investigator  A medical researcher in charge of carrying out a clinical trial's protocol. 

Clinical trial  A clinical trial is a research study to answer specific questions about vaccines or new therapies or new ways of using known treatments. Clinical trials (also called medical research and research studies) are used to determine whether new drugs or treatments are both safe and effective. Carefully conducted clinical trials are the fastest and safest way to find treatments that work in people. Trials are in four phases: Phase I tests a new drug or treatment in a small group; Phase II expands the study to a larger group of people; Phase III expands the study to an even larger group of people; and Phase IV takes place after the drug or treatment has been licensed and marketed. (See Phase III,III, and IV Trials). 

Cohort  In epidemiology, a group of individuals with some characteristics in common. 

Community-based clinical trial (CBCT)   A clinical trial conducted primarily through primary-care physicians rather than academic research facilities. 

Compassionate use  A method of providing experimental therapeutics prior to final FDA approval for use in humans. This procedure is used with very sick individuals who have no other treatment options. Often, case-by-case approval must be obtained from the FDA for "compassionate use" of a drug or therapy. 

Complementary and alternative therapy  Broad range of healing philosophies, approaches, and therapies that Western (conventional) medicine does not commonly use to promote well-being or treat health conditions. Examples include acupuncture, herbs, etc. Internet 

Confidentiality regarding trial participants  Refers to maintaining the confidentiality of trial participants including their personal identity and all personal medical information. The trial participants' consent to the use of records for data verification purposes should be obtained prior to the trial and assurance must be given that confidentiality will be maintained. 

Contraindication  A specific circumstance when the use of certain treatments could be harmful. 

Control  A control is the nature of the intervention control. 

Control group  A group of research subjects who are not treated with the investigational product. The control group may receive a comparative therapy, a placebo or may receive no treatment. The control group study results are compared to the group(s) who receive the investigational products. (See Placebo and Standard treatment).

Controlled trials  Control is a standard against which experimental observations may be evaluated. In clinical trials, one group of participants is given an experimental drug, while another group (i.e., the control group) is given either a standard treatment for the disease or a placebo. 
Back to top

Data 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.

Diagnostic trials Refers to trials that are conducted to find 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.

Dose-ranging study  A clinical trial in which two or more doses of an agent (such as a drug) are tested against each other to determine which dose works best and is least harmful. 

Double-blind study  A clinical trial design in which neither the participating individuals nor the study staff knows which participants are receiving the experimental drug and which are receiving a placebo (or another therapy). Double-blind trials are thought to produce objective results, since the expectations of the doctor and the participant about the experimental drug do not affect the outcome. See Blinded studySingle-blind study, and Placebo.

Drug-drug interaction  A modification of the effect of a drug when administered with another drug. The effect may be an increase or a decrease in the action of either substance, or it may be a positive or negative effect that is not normally associated with either drug. 

DSMB See Data Safety and Monitoring Board
Back to top

Efficacy (Of a drug or treatment). The maximum ability of a drug or treatment to produce a result regardless of dosage. A drug passes efficacy trials if it is effective at the dose tested and against the illness for which it is prescribed. In the procedure mandated by the FDA, Phase II clinical trials gauge efficacy, and Phase III trials confirm it. (See Food and Drug Administration (FDA)Phase II and III Trials).

Eligibility criteria  Summary criteria for participant selection; includes Inclusion and Exclusion criteria. (See Inclusion/exclusion criteria

Empirical Based on experimental data, not on a theory. 

Endpoint  Overall outcome that the protocol is designed to evaluate. Common endpoints are severe toxicity, disease progression, or death. 

Epidemiology  The branch of medical science that deals with the study of incidence and distribution and control of a disease in a population. 

Exclusion/inclusion criteria  See Inclusion/exclusion criteria

Expanded access  Refers to any of the FDA procedures, such as compassionate use, parallel track, and treatment IND that distribute experimental drugs to participants who are failing on currently available treatments for their condition and also are unable to participate in ongoing clinical trials. 

Experimental drug  A drug that is not FDA licensed for use in humans, or as a treatment for a particular condition (See Off-label use). 
Back to top

FDA   See Food and Drug Administration

Food and Drug Administration (FDA) 
The U.S. Department of Health and Human Services agency responsible for ensuring the safety and effectiveness of all drugs, biologics, vaccines, and medical devices, including those used in the diagnosis, treatment, and prevention of HIV infection, AIDS, and AIDS-related opportunistic infections. The FDA also works with the blood banking industry to safeguard the nation's blood supply. Internet address: 
Back to top

There are no terms beginning with the letter "G". 
Back to top

A supposition or assumption advanced as a basis for reasoning or argument, or as a guide to experimental investigation. 
Back to top

Inclusion/exclusion criteria   The medical or social standards determining whether a person may or may not be allowed to enter a clinical trial. These criteria are based on such factors as age, gender, the type and stage of a disease, previous treatment history, and other medical conditions. It is important to note that inclusion and exclusion criteria are not used to reject people personally, but rather to identify appropriate participants and keep them safe.

IND  See Investigational New Drug

Informed consent The process of learning the key facts about a clinical trial before deciding whether or not to participate. It is also a continuing process throughout the study to provide information for participants. To help someone decide whether or not to participate, the doctors and nurses involved in the trial explain the details of the study.

Informed consent document A document that describes the rights of the study participants, and includes details about the study, such as its purpose, duration, required procedures, and key contacts. Risks and potential benefits are explained in the informed consent document. The participant then decides whether or not to sign the document. Informed consent is not a contract, and the participant may withdraw from the trial at any time. 

Institutional Review Board (IRB)  1) A committee of physicians, statisticians, researchers, community advocates, and others that ensures that a clinical trial is ethical and that the rights of study participants are protected. All clinical trials in the U.S. must be approved by an IRB before they begin. 2). Every institution that conducts or supports biomedical or behavioral research involving human participants must, by federal regulation, have an IRB that initially approves and periodically reviews the research in order to protect the rights of human participants. 

Intent to treat   Analysis of clinical trial results that includes all data from participants in the groups to which they were randomized (See Randomization) even if they never received the treatment. 

Intervention name  The generic name of the precise intervention being studied.

Interventions Primary interventions being studied: types of interventions are Drug, Gene Transfer, Vaccine, Behavior, Device, or Procedure. 

Investigational new drug A new drug, antibiotic drug, or biological drug that is used in a clinical investigation. It also includes a biological product used in humans for diagnostic purposes. 

IRB  See Institutional Review Board.
Back to top

There are no terms beginning with the letter "J". 
Back to top 
There are no terms beginning with the letter "K". 
Back to top 
There are no terms beginning with the letter "L". 
Back to top 
See  blind
Back to top

Natural history study  Study of the natural development of something (such as an organism or a disease) over a period of time. 

New Drug Application (NDA) An application submitted by the manufacturer of a drug to the FDA - after clinical trials have been completed - for a license to market the drug for a specified indication. 
Back to top

Off-label use  A drug prescribed for conditions other than those approved by the FDA. 

Open-label trial  A clinical trial in which doctors and participants know which drug or vaccine is being administered. 

Orphan drugs  An FDA category that refers to medications used to treat diseases and conditions that occur rarely. There is little financial incentive for the pharmaceutical industry to develop medications for these diseases or conditions. Orphan drug status, however, gives a manufacturer specific financial incentives to develop and provide such medications. 
Back to top

Peer review  Review of a clinical trial by experts chosen by the study sponsor. These experts review the trials for scientific merit, participant safety, and ethical considerations. 

Pharmacokinetics   The processes (in a living organism) of absorption, distribution, metabolism, and excretion of a drug or vaccine. 

Phase I trials   Initial studies to determine the metabolism and pharmacologic actions of drugs in humans, the side effects associated with increasing doses, and to gain early evidence of effectiveness; may include healthy participants and/or patients. 

Phase II trials   Controlled clinical studies conducted to evaluate the effectiveness of the drug for a particular indication or indications in patients with the disease or condition under study and to determine the common short-term side effects and risks. 

Phase III trials   Controlled and uncontrolled trials that are expanded after preliminary evidence has been obtained suggesting effectiveness of the drug. These expanded trials are intended to gather additional information to evaluate the overall benefit-risk relationship of the drug and to provide an adequate basis for physician labeling.

Phase IV trials  Post-marketing studies to delineate additional information including the drug's risks, benefits, and optimal use. 

Placebo  A placebo is an inactive pill, liquid, or powder that has no treatment value. In clinical trials, experimental treatments are often compared with placebos to assess the treatment's effectiveness. In some studies, the participants in the control group will receive a placebo instead of an active drug or treatment. No sick participant receives a placebo if there is a known beneficial treatment. (See Placebo controlled study, below). 

Placebo controlled study  A method of investigation of drugs in which an inactive substance (the placebo) is given to one group of participants, while the drug being tested is given to another group. The results obtained in the two groups are then compared to see if the investigational treatment is more effective in treating the condition. 

Placebo effect  A physical or emotional change, occurring after a substance is taken or administered, that is not the result of any special property of the substance. The change may be beneficial, reflecting the expectations of the participant and, often, the expectations of the person giving the substance. 

Preclinical   Refers to the testing of experimental drugs in the test tube or in animals - the testing that occurs before trials in humans may be carried out.

Prevention trials  Refers to trials to find better ways to prevent disease in people who have never had the disease or to prevent a disease from returning. These approaches may include medicines, vitamins, vaccines, minerals, or lifestyle changes. 

Protocol   A study plan on which all clinical trials are based. The plan is carefully designed to safeguard the health of the participants as well as answer specific research questions. A protocol describes what types of people may participate in the trial; the schedule of tests, procedures, medications, and dosages; and the length of the study. While in a clinical trial, participants following a protocol are seen regularly by the research staff to monitor their health and to determine the safety and effectiveness of their treatment (See Inclusion/exclusion criteria). 
Back to top

Quality of life trials (or Supportive Care trials)   Refers to trials that explore ways to improve comfort and quality of life for individuals with a chronic illness. 
Back to top

Randomization   A method based on chance by which study participants are assigned to a treatment group. Randomization minimizes the differences among groups by equally distributing people with particular characteristics among all the trial arms. The researchers do not know which treatment is better. From what is known at the time, any one of the treatments chosen could be of benefit to the participant (See Arm). 

Randomized trial   A study in which participants are randomly (i.e., by chance) assigned to one of two or more treatment arms of a clinical trial. Occasionally placebos are utilized. (See Arm and Placebo). 

Risk-benefit ratio  The risk to individual participants versus the potential benefits. The risk/benefit ratio may differ depending on the condition being treated. 
Back to top

Screening trials  Refers to trials which test the best way to detect certain diseases or health conditions. 

Side effects  Any undesired actions or effects 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 (See Adverse reaction).

Single-blind study   A study in which one party, either the investigator or participant, is unaware of what medication the participant is taking (See Blind and Double-blind study).

Standard treatment  A treatment currently in wide use and approved by the FDA, considered to be effective in the treatment of a specific disease or condition. 

Standards of care   Treatment regimen or medical management based on state of the art participant care.

Statistical significance  The probability that an event or difference occurred by chance alone. In clinical trials, the level of statistical significance depends on the number of participants studied and the observations made, as well as the magnitude of differences observed.

Study endpoint  A primary or secondary outcome used to judge the effectiveness of a treatment.

Study type 
Treatment trials test experimental treatments, new combinations of drugs, or new approaches to surgery or radiation therapy. 
Prevention trials look for better ways to prevent disease in people who have never had the disease or to prevent a disease from returning. These approaches may include medicines, vitamins, vaccines, minerals, or lifestyle changes. 
Diagnostic trials are conducted to find better tests or procedures for diagnosing a particular disease or condition. 
Screening trials test the best way to detect certain diseases or health conditions. 
Quality of Life trials (or Supportive Care trials) explore ways to improve comfort and the quality of life for individuals with a chronic illness. 
Back to top

Toxicity  An adverse effect produced by a drug that is detrimental to the participant's health. The level of toxicity associated with a drug will vary depending on the condition which the drug is used to treat. 

Treatment IND  IND stands for Investigational New Drug application, which is part of the process to get approval from the FDA for marketing a new prescription drug in the U.S. It makes promising new drugs available to desperately ill participants as early in the drug development process as possible. Treatment INDs are made available to participants before general marketing begins, typically during Phase III studies. To be considered for a treatment IND a participant cannot be eligible to be in the definitive clinical trial. 

Treatment trials   Refers to trials which test new treatments, new combinations of drugs, or new approaches to surgery or radiation therapy. 
Back to top

There are no terms beginning with the letter "U". 
There are no terms beginning with the letter "V". 

There are no terms beginning with the letter "W".

There are no terms beginning with the letter "X". 

There are no terms beginning with the letter "Y". 

There are no terms beginning with the letter "Z".
Back to top



Center for Clinical and Translational Sciences

Clinical Trials Resource Center (CTRC)
7000 Fannin Street, Suite 795

Houston, Texas 77030
phone 713-500-3622
fax 713-500-0334