Understanding the Four Phases of Clinical Trials

Phase I

Phase I clinical studies are the first stage of drug testing on humans. They typically involve healthy volunteers and require in-patient stay for varying lengths of time. The trials typically test the safety, dosing and tolerability of certain medications.

Phase II

Once the drug’s safety has been determined in the Phase I trial, Phase II trials are performed on larger groups of volunteers to test for efficacy and toxicity.

Phase III

During this phase, trials are conducted across multiple trial centers on large groups of participants to definitively conclude a drug’s efficacy and monitor side effects.

Phase IV

Phase IV trials are post marketing studies after the drug is cleared for sale to further outline benefits and risks.