Why are new drugs tested on laboratory animals before studies in humans?

New drugs are tested on laboratory animals primarily to evaluate safety and potential toxicity before human clinical trials begin. These preclinical studies are designed to identify neurological, physiological, biochemical, and hematological abnormalities, allowing researchers to select the most suitable chemical compounds and dosages for further development.123

By observing how a drug interacts with the systems and organs of animals, scientists aim to predict potential human reactions and minimize risks. For instance, acute toxicity tests in two mammalian species are generally required before Phase 1 human safety studies can commence. This process is intended to prevent adverse outcomes, such as "vaccine enhancement," where a treatment might inadvertently worsen a condition.314

However, the necessity and reliability of animal testing are subjects of significant ethical and scientific debate. Critics point out that animal models do not always accurately predict human responses, noting that many drugs successful in animal trials fail in human testing. Ethical principles demand that we balance the pursuit of medical progress with the moral imperative to minimize animal suffering, leading to the widespread adoption of the "three Rs" principle: replacement, reduction, and refinement.56