Before a drug may be tested on humans, pre-clinical studies must be conducted either in vitro but usually in vivo on animals to mainly determine if the drug is safe. Animal studies are also done to provide data regarding absorption, distribution, metabolism ,toxicity and excretion of a new drug / molecule. Different strengths of the experimental drug are administered to test the drug's ability to improve performance and behavior in animals, and to reveal harmful side-effects that may occur. Based on the results obtained from these initial studies , the drug compound may be slightly modified to make it more effective. The duration of the study can range from 1-6 years depending on the proposed action of the new drug and also to make sure that the drug can be safely tried out on humans.
After the drug is found beneficial on animal models the sponsor of the new molecule/ drug files the IND (Investigational New Drug) application. In this application, the pharmaceutical company should describe its plan of action for the next phase of the trial to be carried out in humans, including details such as, how many participants the study will involve; what criteria will be used for enrolling participants; where the studies will take place; and, how drug safety and efficacy will be measured.
If the above details is accepted by the Licensing Authority (Drug Controller of India - DCGI ) or FDA , drug testing in human subjects can begin within 30 days.