Forensic toxicology is the only laboratory discipline in which scientific results are used to explain a person's behavior before, during, or after the commission of a crime—or perhaps the causing of a traffic accident. It is part of the science of pharmacology, which is concerned with the quantities and effects of various drugs and poisons on human beings. In forensic toxicology the main interest is the extent to which drugs and poisons may have contributed to impairment or death. Drags cover both legal (such as prescription medicines and alcohol) and controlled substances (such as cocaine, heroin or the newer drugs).

Forensic toxicology has developed as a forensic science in recent years and is now widely used to assist in death investigations, in civil and criminal matters involving drug use, in drugs of abuse testing in correctional settings and custodial medicine, in road and work-place safety as well as in matters involving environmental pollution.