Phases of a Clinical Trial
Phase I focuses on safety, tolerance and pharmacokinetics. It usually involves several dozen patients
Phase II focuses on efficacy, dosing regimens, and safety. The double-blind/placebo controlled protocol begins here. It usually involves several hundred patients
Phase III focuses on dosing and efficacy for specific symptoms/indications, as well as continuing to assess side effects. It involves several hundred to a thousand patients
Phase IV, a post-marketing phase, focuses on adverse reactions, long term effects of drug, and/or comparisons to other products.