Toxicology

Toxicology studies the harmful effects of chemical, physical and biological agents on living organisms, from medicines and pesticides to metals, plant and animal toxins, and industrial pollutants. Its guiding principle, traced back to the Renaissance physician Paracelsus, is that the dose makes the poison: nearly any substance, even water, can cause harm in a large enough amount. Toxicologists therefore map dose-response relationships to find the exposure at which damage begins, and they study how a substance enters the body, travels through it, is metabolized and excreted, and by what mechanism it injures cells and organs.

The field has several branches. Clinical toxicology diagnoses and treats poisoning and overdose, sometimes with specific antidotes. Regulatory and environmental toxicology test chemicals for safety, including whether they cause cancer or birth defects, and inform exposure limits for food, drinking water and workplaces; researchers increasingly use cell-based tests, computer models and organisms such as zebrafish in place of mammals. Forensic toxicology analyzes blood, urine, the fluid inside the eye and other samples, often after death, to show whether alcohol, drugs or poisons played a part in a death, a crash or a crime.

Toxicology is often described as a branch of pharmacology, which studies the intended effects of drugs; the two meet in questions of safe dosing and side effects.