What is a clinical trial?

A clinical trial is a research study that involves people to evaluate the effectiveness of a therapeutic, invasive, surgical or care management intervention through the process of randomization assigning each subject to treatment group by chance in order to balance known and unknown treatment variables that may influence the disease process and response to treatment.


Phase I

In a phase I clinical study, the investigational new drug is tested for the first time in human subjects for the purpose of evaluating the safety of the drug.  The safety profile of the investigational agent is determined by monitoring the metabolism and pharmacologic actions of the drug and determining the maximum tolerated dose in a small population of subjects (20 to 80).  (21 CRF 312.21(a)

    Phase II

    In a phase II clinical trial the purpose of the study is to evaluate the effectiveness and safety of the investigational drug in a larger group of patients (typically 100 to 300)  by determining the most effective tolerated dose and monitoring common side effects and risks associated with the drug.  (21 CRF 312.21(b)

    Phase III

    In a phase III clinical trial the investigational drug has demonstrated effectiveness and the main purpose is to obtain additional information regarding the drug’s safety and effectiveness that is needed for evaluating the risk and benefit of the drug which is necessary for the labeling and marking of the drug. Typically phase III trials are large (300 to 1000 patients) randomized, multi-center trials. (21 CRF 312.21(c)

    Phase IV

    In a phase IV clinical trial the study is conducted after the product has been approved by the FDA for the purpose to gain additional information about the drugs risks, benefits, optimal use and evaluation of the drug in different patient populations. (21 CRF 314.80)