Common Terms You Should Know When Enrolling in a Clinical Trial

Clinical trials, also known as clinical studies or clinical research, are studies that explore whether a medical strategy, treatment, or device is safe and effective for humans. When deciding whether to enroll in a clinical trial, you will likely encounter many terms related to clinical research and what the specific trial entails. Some terms are fairly standard across trials, regardless of the type of trial or what is being evaluated. When evaluating trial options, it’s important to understand what is involved with the clinical trial. This is also required before consenting to enroll on a trial (a term called “informed consent”). To help you navigate through the process, we’ve outlined common clinical trial terms that you should know. 

Adverse Event: Any undesirable experience associated with a drug or procedure, also sometimes described as a side effect or negative reaction. Adverse events can range from mild to severe. Serious adverse events are those that can cause temporary or permanent disability and may result in hospitalization or death.

Baseline Characteristics: Data collected at the beginning of a clinical study for all participants and for each arm or comparison group. These data include demographics, such as age, race, and gender, and any study-specific measures (e.g. systolic blood pressure, prior antidepressant treatment).

Blinding or Masking: When those involved in the trial are not aware of the treatment assignments. There can be many different types of blinding. “Single Blind” means that the study participants do not know to which treatment group they have been assigned. “Double Blind” means that both the study participants and the investigators don’t know who has been assigned to each treatment group.

Compassionate Use: A method of providing experimental therapeutics prior to final regulatory agency (FDA) approval for use in humans. This procedure is used with very sick individuals who have no other treatment options available. Often, case-by-case approval must be obtained by the patient’s physician from the regulatory agency for “compassionate use” of an experimental drug or therapy. 

Confidentiality: This refers to the practice of maintaining 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 participant names or reveal any identifying information without obtaining additional consent.

Control Group: The group of participants that receives standard of care treatment. The control group may also be comprised of healthy volunteers.

Eligibility Criteria: This refers to the factors or restrictions that determine who can participate in the clinical trial. This is different for every trial and can sometimes be referred to as the Inclusion Criteria and Exclusion Criteria.

Experimental Group: The group of participants in a study that receive the experimental treatment or study intervention.

First-In-Human Study: A clinical trial where a medical procedure or medicinal product that has been previously developed and assessed through laboratory model or animal testing is tested on human subjects for the first time.

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 and effective.

Informed Consent: When a participant provides informed consent, it means that he or she has learned the key facts about a research study, including the possible risks and benefits, and agrees to take part in it.

Intervention: The treatment, drug or procedure that is being studied in the clinical trial. This term is typically used when compared to a control or standard of care treatment arm. An “Interventional” trial is a term used to describe clinical trials studying a treatment, drug or procedure. This is different from an “Observational” study (see definition below).

Observational Study: In an observational study, investigators assess health outcomes in groups of participants according to a research plan or protocol. Participants may receive diagnostic or other types of interventions as part of their routine medical care, but the investigator does not assign participants to specific interventions or treatments.

Outcome Measure: A planned measurement described in the protocol that is used to determine the effect of interventions on participants in a clinical trial. For observational studies, a measurement or observation is used to describe patterns of diseases or traits, or associations with exposures, risk factors, or treatment.  

Phase: The categories that each clinical trial can fall into based on what properties of the treatment are being studied in the trial and how many participants are involved. There are typically four phases of a clinical trial. Phase I is the administration of a drug or device to a small group to identify possible side effects and determine proper dose. Phase II is done to gauge whether the treatment is effective while continuing to evaluate safety. Phase III compares a new drug or device against the current standard of care. Phase III trials have the potential to lead to Food and Drug Administration (FDA) approvals. Finally, phase IV trials are done after FDA approvals. Sometimes the FDA will require additional safety information to be collected after approval. Phase IV trials are often referred to as “post-market surveillance,” which look to identify problems that were not observed or recognized before approval.

Placebo: A substance that does not contain active ingredients and is made to be physically indistinguishable from the actual drug being studied.

Protocol: The written description of the clinical trial.

Principal Investigator (PI): A medical professional who leads the conduct of a clinical trial at a study site. This person is the lead researcher for the project. The phrase is also often used as a synonym for “head of the laboratory” or “research group leader.”

Sponsor: The sponsor is the organization or person who oversees the clinical study and is responsible for analyzing the study data. Often, the sponsor will also provide financial support for the trial.

Subject: Any participant in a study.

Treatment Arm: A group or subgroup of participants in a clinical trial. Each group receives a specific intervention, study drug dose, or sometimes no intervention, according to the study protocol.

Randomization: The process in which study participants are randomly assigned to different treatment groups. This is to ensure that everybody has an equal chance of being a part of each treatment or control group.

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