Drug discovery is a multifaceted process involving extensive screening, testing, and optimization of lead compounds to identify potential new drugs for therapeutic use. It combines several approaches, including screening large numbers of natural products, chemical modification of known active molecules, identification of new drug targets, and rational design based on biological mechanisms and drug-receptor structure. These approaches are carried out in both academic research laboratories and the pharmaceutical industry.

The process begins with drug screening, which involves various assays to evaluate the pharmacological profile and activity of the drug at different levels, such as molecular, cellular, organ system, and whole animal levels. The candidate molecule undergoes extensive testing to determine its mechanism of action, selectivity, and potential toxic effects. Animal models of human diseases are used to select compounds for further development, especially in cases where preclinical models are well-established.

The candidate compound is screened for its activity on the target protein at the molecular level using techniques like receptor binding assays. Cell function studies determine whether the drug acts as an agonist, partial agonist, inverse agonist, or antagonist at relevant receptors. Whole animal studies assess the drug's effects on organ systems and disease models.

Lead compounds with the desired pharmacological activity and selectivity are identified during the screening and lead generation processes. These lead compounds serve as the basis for further chemical modification and optimization in the lead optimization phase. Lead optimization involves a range of tests and assays to increase the potency of the compound, optimize selectivity, and evaluate other characteristics, such as pharmacokinetic properties. Animal studies assess the compound's activity in vivo, potential adverse effects, genotoxicity, and oral availability.

Only a small percentage of drug discovery projects succeed in generating a drug candidate, and the lead optimization phase can be time-consuming and challenging. Many factors can hinder progress, including the inability to optimize lead compounds or the failure to produce desired effects in animal models. Successful drug candidates proceed to the next phase, preclinical development, before entering human clinical trials.