Drug development is a process during which drug candidates are extensively tested before they are approved for commercial use. In preclinical development, drugs are tested in vivo on animal models for different pharmacological properties, such as safety, preliminary toxicity, pharmacokinetics, and pharmacodynamics. First, the drugs are checked to ensure they produce no acute hazardous effects such as bronchoconstriction, blood pressure changes and cardiac dysrhythmia. Next, the drugs are evaluated for their preliminary toxicity, monitoring for genotoxicity, reproductive toxicity, maximum tolerated dose, weight loss and possible tissue damage. Drugs are also tested for pharmacological properties, where drugs' absorption, distribution, metabolism, and elimination are studied in the animal model. The next critical step is the large-scale synthesis of drugs with reproducible purity. The stability of the drug molecules is tested under various conditions, and suitable formulations are developed. Successful drug candidates from these preclinical screenings are passed for human testing in clinical trials.