New drug development involves animal toxicity studies followed by clinical trial in humans. Potentially useful compounds are studied in animals to evaluate desired effects and toxicity. Animal toxicity studies are done to see whether the chemical is safe or not. For all new drugs, it is mandatory to do toxicity studies in animals. After that the drug enters various phases of clinical trials. Drug development is an extremely arduous, highly technical, time-consuming and very expensive process. Clinical trial is defined as “a carefully and ethically designed experiment with the aim of answering some precisely framed questions”. Clinical trial is systematic study of pharmaceutical products on human subjects—(whether patients or non-patient volunteers)—in order to discover or verify the clinical, pharmacological (including pharmacodynamics/pharmacokinetics) and/or adverse effects, with the object of determining their safety and/or efficacy. There can be 4–5 phases of clinical trials, i.e. phase 0, phase I, phase II—exploratory trials, phase III—confirmatory trials and phase IV.