The clinical trial approval process is classified into four progressive phases of testing in order to test the efficacy and safety of a treatment or method. Each phase is treated as a different clinical trial and can last from a few months to a few years. These trials are often conducted in clinics run by contract research organizations (CRO's) and are observed by a full time staff. This phasing approach allows researchers the ability to test methods and treatments on increasingly large populations of patients while keeping risk to patients' health as low as possible.
Phase 1 trials are the first phase of human testing. During this inital phase of testing, researchers test the methods and treatments for safety (side effects), dosage (if applicable), as well as the most effective delivery method (e.g. IV or pill). Phase 1 is often the smallest phase, with groups of up to 100 patients participating, and can contain healthy as well as unhealthy patients.
After the drug has been deemed safe for further testing, treatments proceed to Phase 2 clinical trials. Phase 2 trials typically test larger groups (100-300 patients) and aim to test the effectiveness of the treatment. As such, many Phase 2 clinical trials will randomize patients to conduct single or double-blind studies to determine the treatment's effictiveness compared to a placebo. Researchers will also continue to monitor the patient health in order to observe any side effects the patients may exhibit.
After being deemed effective (at least for a subset of patients) in Phase 2, the treatment progress to the largest and most complex phase - Phase 3. In this phase, researchers will test the effectiveness of the treatment as compared to the current "gold standard" treatment available in a very large patient group.
Sometimes deemed the "pre-marketing phase", study sponsors will also measure consumer response to the treatment during this phase in order to determine its viability on the open market. Though infrequent, some trials may actually be actively marketed during this phase. If the trial is found to have adverse effects, however, all materials must
This phase occurs after a drug has been approved and is actively being sold. The goal of this phase is to observe the treatment "in the wild" for uncaught short or long-term side effects and also to provide support to consumers upon approval. Harmful side effects discovered may cause the treatment to be recalled or restricted to certain uses where the effects are controlled or eliminated.