Clinical development focuses on how the drug will interact with the human body and encompasses four key phases of clinical trials, each serving a specific purpose in assessing the safety and effectiveness of new drugs. These phases overlap and build upon one another. Phase I involves a small group of healthy volunteers (typically 20-80 individuals) or, in cases where significant toxicity is expected, patients with the targeted disease, such as cancer or AIDS. The volunteers are tested for potential adverse effects, tolerability, and pharmacokinetic properties. Phase II expands to include a larger group of patients (around 100-300) to evaluate pharmacodynamic effects and identify potential therapeutic candidates. Phase III comprises double-blind, randomized trials involving thousands of patients to compare the new drug with existing alternatives or placebos. These trials are comprehensive, costly, and time-consuming. Finally, Phase IV consists of post-marketing surveillance to monitor rare or long-term adverse effects in a large patient population.

Clinical trials must adhere to Good Clinical Practice (GCP) guidelines, ensuring meticulous patient group selection, data collection, statistical analysis, and documentation. Phase III trials increasingly incorporate pharmacoeconomic analysis to assess clinical and economic benefits. Upon completion of Phase III, the drug undergoes submission to regulatory authorities for licensing, accompanied by a detailed dossier of preclinical and clinical data.

The drug development process, including clinical trials, spans 7 to 12 years. The FDA oversees the approval and monitoring of new drugs, requiring manufacturers to undergo in vitro and in vivo testing before applying for Investigational New Drug (IND) status. Approval from regulatory authorities can take a year or longer, and only about two-thirds of submissions receive marketing approval.