Drug Toxicology is the study of the effect of chemical and biological substances on human health.Toxicological studies can involve direct testing on animals, epidemiological studies on humans, or in vitro studies, in which chemicals and potential target species represented by tissue cultures are mixed directly in the laboratory. The evaluation of drug safety and toxicology has benefited in recent years from biomarker applications, particularly in the area of biomarker discovery. As the number of drugs and drug targets grows, there is a commensurate need for readily measurable markers that can provide an early indicator of undesirable side effects. Toxicological risk-assessment process for pharmaceutical or other compounds is always incomplete and associated with uncertainties.