A clinical trial is a biomedical or health-related research study carried out with humans to determine the safety and efficacy of a new drug or treatment. A clinical trial can only take place once information has been gathered on the quality of the drug and its non-clinical safety.
Clinical trials can vary in size from a single center in a single country to multiple centers in multiple countries. In the U.S., the Food and Drug Administration (FDA) is responsible for establishing regulations and guidelines for clinical research and for overseeing clinical trials in order to protect the rights of participants and to verify the quality and integrity of the data. The FDA also reviews New Drug Applications, which are submitted by the drug sponsor at the conclusion of a Phase III trial to seek approval for marketing of a new drug in the U.S.
Clinical trials are conducted in phases; the trials at each phase have a different purpose and help researchers to answer different questions. The four phases of clinical trials are:
Phase I: Researchers test an experimental drug in a small group of people for the first time to evaluate its safety, determine a safe dosage range, and identify any side effects. Usually, healthy participants are enrolled in Phase I studies but in cancer, Phase I trials are conducted in patients rather than healthy volunteers.
Phase II: Phase II trials continue to test the safety of the drug, and begin to evaluate how well the experimental drug works in treating a certain disease or condition. The drug is given to a larger group of people and may involve a control group who receive either the current standard treatment or a placebo.
Phase III: Phase III trials are longer-term studies. The experimental drug is given to large groups of people (several hundred to thousands) to gather additional information about effectiveness, safety and side effects, to compare it to other treatments commonly used for the disease or condition, and to collect information that will allow the drug to be used safely. At the end of most Phase III trials, the new drug will be found to be inferior, equal or superior to the standard treatment. Based on favorable results, the drug may at this phase be approved to be sold to the public.
Phase IV: A Phase IV trial may take place after the drug has been on the market to further examine the drug’s risks, benefits and optimal use in ‘real-life’ conditions. Phase IV studies can also include trials of different doses or schedules of administration, other stages of disease, cost studies, quality-of-studies or use of the drug over a longer period of time.
A clinical trial may be ‘blinded’ so that the expectations of a drug’s effects will not influence observed results. In a ‘single-blinded’ trial, participants do not know which treatment they are receiving until the end of the study. In a ‘double-blinded’ study, neither the researchers nor the participants know which treatment the participant has received until the end of the study.