Adverse Event (also known as "adverse effect" or "side effect"):

An adverse event is a negative reaction that a participant may experience while taking a study drug or receiving some type of study treatment. Adverse events may happen suddenly or develop over time (even after the study is complete). Adverse events include minor events such as a sore throat as well as major events such as the death of a participant.

Blind (or Double-Blind) Study:

In a blind study, there is more than one drug/treatment being used, and you will not be told which one you are receiving. In a double-blind study neither you nor the study staff will know what type of drug/treatment you are receiving. Blind and double-blind studies are performed so that the procedures and results of a study are not unnecessarily influenced by you or the study staff. For example, it might be difficult for you to continue following the study procedures if you were aware that your study medication/treatment was actually a placebo.

Inclusion/Exclusion Criteria:

Inclusion/Exclusion criteria are the standards used to determine whether or not people can participate in research studies. These criteria are based on characteristics such as age, gender, medical history and the medication that a person is currently taking. The purpose of inclusion/exclusion criteria is to keep people safe and to help the study staff select the best participants for a study. For example, a person with a history of high blood pressure should not be participating in the study of a drug that might increase blood pressure. Inclusion criteria are the characteristics that you must have in order to participate. Exclusion criteria are the characteristics that you must not have in order to participate.

Informed Consent Document (ICD, also known as "consent form"):

The ICD is a document that the study staff will give you that explains all of the main details of a study, including the purpose, the risks and possible benefits, what procedures will take place, how your privacy will be protected, if and how much you will be paid, how long the study will take to complete, and what alternatives you have instead of participating in the study.

No study procedures may be performed on you until you sign an informed consent document. If all of your questions have not been answered in that document, the study staff is required to answer any other questions you may have. If you sign an informed consent document, you can decide to withdraw your decision to participate at any time, for any reason, with no penalty to you or your medical care.

Please see Participant FAQs for a description of "informed consent," the process that involves signing the informed consent document.

Institutional Review Board (IRB):

See Participant FAQs for more information.

Open-label Study:

In an open-label study, both you and the principal investigator (or study doctor) know which study drug/treatment you are receiving.


A placebo is something that looks like a drug/treatment, but does not actually contain any medicine or offer possible treatment. Sometimes people call the placebo a "sugar pill," but a placebo is not always in the form of a pill. Placebos can also be medical devices or administered with injections. Placebos are used in studies to make sure that the real study drug or treatment is more effective than taking nothing at all.

Principal Investigator (PI, also known as "study doctor"):

The principal investigator, or PI, is the main researcher in charge of a study. The PI agrees to follow the protocol and commits to protecting the safety of the participants in the study. The PI, usually a medical doctor, is responsible for what happens during the study, including the actions of every member of the study staff. The study staff may include one or more sub-investigators, study coordinators, and other research professionals. 

The PI may be a physician who also conducts research studies or the PI may be an individual who only conducts research studies. Your personal physician may be a PI on a study, and he/she may ask you to participate in one of his/her research studies.


A protocol is a detailed plan that is designed for conducting a research study properly. It explains the questions that the research is trying to answer as well as the steps and rules that the researchers should follow to get accurate results and to help ensure the safety of the participants. If a protocol is not followed correctly, the study results could be incorrect and/or the research participants could be harmed.


Some research studies have groups of participants who are receiving different doses or types of drug/treatment. These studies are called "randomized" studies. When participants are "randomized" to groups, they are assigned by chance (like flipping a coin) to one of 2 or more groups. Randomization, the act of assigning participants to groups, ensures that the study is being fair to the participants, particularly when some groups will be receiving placebo. The groups in a randomized study are sometimes called "treatment arms" (see below).


Screening refers to the period when tests are performed and questions are asked to see if you can participate in a research study. During the screening (sometimes called a "screening period" or "screening visit") the study staff will find out whether or not you meet the inclusion/exclusion criteria. The screening may take place during one visit or over the course of several visits.

Study Phases:

Studies are often divided into four categories or phases:

Phase I studies are usually performed on a very small group of people because the drugs or treatments have only been tested with animals. Phase I researchers can not accurately predict how humans will react and whether or not they may be harmed. Small groups are used in Phase I studies to reduce the number of people who are taking the risks involved with a new drug or possible treatment. This phase is often used to study the dose or amount of drug that humans can tolerate. Both healthy participants and patients can participate in Phase I studies.

Phase II studies take place when a drug or treatment has been used in Phase I studies and it did not cause major harm or create significant risk to humans. Phase II is used to see if a drug or treatment can treat a disease or health problem. There are usually many more participants involved, and they last longer when compared to Phase I studies. Common side effects, risks and treatment possibilities are examined during Phase II studies.

Phase III studies are the final stage a study has to go through before a drug/treatment or device is given approval by the FDA (U.S. Food and Drug Administration). Phase III studies are often much longer (even years longer) than previous phases, and they may involve thousands of people across the world. After this phase is complete, if results are still promising, a drug or device company can seek FDA approval to sell the drug in the United States.

Phase IV studies use drugs or devices that have already been approved by the FDA to see if they can be used in other ways. For example, a researcher might combine an FDA-approved drug with another drug, or study an FDA-approved drug to see if it can be used to treat another type of disease or health problem.

Treatment Arm:

Treatment arms are different study groups that are used in randomized studies (see Randomization above). Sometimes a research study may require different groups of participants to receive different types of treatment. There are many types of treatment arms, including groups that receive different doses of study drug, groups that receive a completely different type of drug/treatment, and groups that receive placebo instead of a real drug/treatment.



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