Understanding the Phases of Clinical Trials
Prescription drugs don’t just show up on pharmacy shelves one day. Each one is first subjected to thorough scientific testing during what are known as clinical trials.
Clinical trials are conducted in phases, each of which is designed to assess a treatment or drug’s safety as well as answer different questions researchers may have about a drug or treatment. Clinical trial phases range from phase 0 to phase 4.
Focus: Safety and Side Effects
In a Phase 1 clinical trial, an experimental drug is given to humans, often for the first time. The purpose of this phase is to determine the most frequent and serious side effects of the drug. During this phase of the study, investigators may also begin to determine dosing of the drug.
Participants are usually healthy, though for some drugs, the first trials in human participants are patients with the disease that the experimental drug is intended to treat.
Focus: Effectiveness and dosage
In this phase, researchers work to collect preliminary evidence that a treatment is effective for the disease it is intended to treat. They also determine the most effective dosages for the experimental drug and the most appropriate method of delivering it (e.g., tablets, extended release capsules, infusions, injections, etc.). Information about the experimental drug’s safety, side effects, and potential risks is collected, too.
Participants studied in Phase 2 clinical trials are usually patients who have the medical condition that the experimental drug is intended to treat.
Phase 3 trials test the results of earlier trials in larger populations. Researchers gather additional information about the effectiveness and safety of an experimental drug. These trials are often randomized and "single-blinded" or "double-blinded," meaning either the investigator or the participant (single) or both (double) do not know who in the trial is getting the experimental drug versus a placebo (commonly referred to as a sugar pill).
Phase 3 trials will usually involve several hundred to several thousand participants with many physician-investigators. Participants will typically have the disease the experimental drug is intended to treat.
Focus: Long-term effectiveness and safety
Also called post-marketing studies, phase 4 trials are conducted after the drug has been approved for marketing by the FDA and made available to the public. Researchers collect additional information about long-term risks, benefits, optimal use, and use in different populations.
These trials often involve a large number of participants from diverse populations. Safety information from phase 4 trials and beyond is reported to the FDA to allow continued monitoring of the drug’s safety even after approval.