The process of drug development consists of five phases.
Pre-clinical phase: After a substance or compound is developed, extensive laboratory research is conducted and the product or compound extensively tested in animals and human cells. An approval is sought from the FDA (Food and Drug Administration) by the pharmaceutical company to initiate testing in humans.
After the FDA approves testing in humans, Phase I is where investigation on the safety of the new drug in the human body begins. Since this will be the first time the drug is being tested in humans, its sole purpose is to examine how the drug is absorbed, metabolized, and excreted in the human body. A group of 20-80 healthy volunteers is selected during this phase.
If the drug passes Phase I, the trial will then proceed to Phase II. Since the drug is tested to be safe, the number of volunteers, who meet the targeted criteria for the trial, is increased. The volunteers are randomized to different treatment arms, which include the drug currently being investigated, a drug that has already been approved by the FDA, and a placebo or inactive drug.
Phase III studies are randomized controlled trials on large patient groups (300-3,000 or more depending upon the condition) and are aimed at being the definitive assessment of the efficacy of the new therapy.
Phase IV: It is the post-marketing safety surveillance and ongoing technical support of a drug. It is designed to detect any rare or long-term adverse effects over a large patient population and timescale than was possible during the initial clinical trials.