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There are four phases of a clinical trial:
Phase I: In this phase, it is usually the first time a new treatment, drug or device is used in humans. The treatment under investigation is given to a small number of research volunteers at a very low dose or setting, and is increased over time according to the response. The purpose of this phase is to determine the best way to give the new treatment - either by mouth, injected into the blood or injected into the muscle - and how much of it can be given safely.
Phase II: Phase II helps to determine the effect of a research treatment on a particular disease or condition. Phase II trials involve the development of a protocol, or plan, about how the trial will be conducted and how the data will be analyzed. These plans are submitted to the Institutional Review Board (IRB), who must approve the protocol before the clinical trial begins. The IRB is a group of health professionals and non-medical persons whose job it is to review and monitor clinical research to protect the safety and rights of participants. Some research is also reviewed and monitored by federal agencies, such as the National Institutes of Health or the Food and Drug Administration. In a Phase II clinical trial, there may or may not be a control group. Control groups receive standard, current care. Treatment groups receive the experimental therapy.
Phase III: This phase compares the new treatment with the standard treatment on a larger group of research volunteers to determine effectiveness, dosing, and optimal characteristics of a treatment, drug or device. The same review and approval process takes place as in a Phase II clinical trial. In this phase, there is most likely a control group and a treatment group. Research volunteers are randomized, or assigned to a group based on chance.
Phase IV: This phase of research is conducted after approval has been given by the Food and Drug Administration. The purpose of a Phase IV clinical trial is to continue testing the study drug or treatment to collect information about its side effects in various populations and any side effects associated with long-term use.