Participating in Clinical Trials

Terms to Know

Terms Used in Clinical Trials

  • protocol
  • eligibility (inclusion or exclusion) criteria
  • placebo
  • standard treatment
  • side effects
  • experimental group and control group
  • randomized controlled trial
  • double-blind study


A protocol is the detailed study plan that will be followed to answer specific research questions. It describes

  • what type of people are needed in the trial
  • the schedule of tests, procedures, drugs, and dosages
  • how long the study will last
  • how to measure the beneficial and harmful effects.

Eligibility (Inclusion or Exclusion) Criteria

Eligibility (inclusion or exclusion) criteria are the set of social and medical characteristics researchers use to decide who can take part in a clinical trial. These may include

  • a person's age and gender
  • the type and stage of their disease
  • previous treatment history
  • any other medical conditions.


A placebo, sometimes called a sugar pill, is a substance that looks like the experimental drug but has no active ingredients. Researchers compare the effects of experimental treatments with placebos.

Standard Treatment

Standard treatment is a therapy that is

  • effective for a specific disease or condition
  • currently in wide use
  • usually approved by the U.S. Food and Drug Administration
  • used to compare with the newer treatment, to see which is better.

Side Effects

Side effects are unwanted or unexpected negative effects, such as a headache or skin irritation, caused by taking a drug or treatment. Side effects can be serious and even life threatening.

Experimental Group and Control Group

The experimental group gets the experimental product and the control group gets the standard treatment, a placebo, or no treatment at all. The results from the two groups are compared to determine the effectiveness of the experimental product.

Randomized Controlled Trial (RCT)

A randomized controlled trial (RCT) is a study in which participants are randomly (that is, by chance) assigned to either the control group or the experimental group. Neither the researchers nor the participants can choose the group in which they are placed.

Double-blind Study

In a "double-blind" study, the researchers and participants won't know who has been placed into the experimental group until the study is over.

For more clinical trial terms, go to the Glossary.