Clinical trials for new treatments are always tested through several steps called phases. The typical phases of clinical trials are:
Phase 1: Safety
Phase 1 focuses on the safety of a drug. It is usually conducted with healthy volunteers with the goal to determine the drug’s most frequent and serious adverse events, at what dose level and, often, how the drug is broken down and excreted by the body. These trials usually involve a small number of participants.
Phase 2: Safety & Efficacy
A Phase 2 clinical trial is used to gather preliminary data on whether a drug works in people who have a certain condition/disease (that is, the drug’s effectiveness). Participants receiving the drug may be compared to similar participants receiving an inactive substance (called a placebo) or a different drug. Safety continues to be evaluated and short-term adverse events are studied. Usually, fewer than 100 people participate Phase 2 trials.
Phase 3: Safety & Efficacy
Phase 3 gathers more information about a drug’s safety and effectiveness by studying different populations with what would be considered a drug, drug combination, and dosage that might be used in the clinic (i.e. commercially). The drug being studied is compared to a placebo or competitive drug and uses very high standards to ensure the quality of the results – commonly used elements of high-quality clinical study design include being randomized, double-blind, and placebo-controlled. Phase 3 trials may include people from all over the world. The usual number of people in the trial is several hundred to several thousand.
A Phase 3 study is typically undertaken only with expectation that the drug and study design has a good prospect of proving the drug’s clinical utility and being given regulatory and marketing approval by an agency such as the US Food and Drug Administration (FDA).
Phase 4: Additional Research
Phase 4 is sometimes initiated after the FDA has approved a drug for marketing. These trials gather additional information about a drug’s safety, efficacy, or optimal use.