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Principles of Toxicology

The Dose Makes the Poison

Paracelsus, the 16th-century physician, established the foundational principle: 'All things are poison, and nothing is without poison; the dose alone makes a thing not a poison.' Even water is lethal in extreme quantities (hyponatremia). Toxicology quantifies this principle through the dose-response relationship—the mathematical function relating the amount of a substance received (dose) to the magnitude of the biological effect (response). A dose-response curve typically shows a threshold below which no adverse effect occurs, followed by a rising curve of increasing severity. The LD50 (lethal dose for 50% of a test population) is the most common measure of acute toxicity: table salt has an LD50 of 3,000 mg/kg in rats, while botulinum toxin has an LD50 of 0.001 mg/kg—a three-million-fold difference.

Principles of Toxicology

The Dose Makes the Poison

Paracelsus, the 16th-century physician, established the foundational principle: 'All things are poison, and nothing is without poison; the dose alone makes a thing not a poison.' Even water is lethal in extreme quantities (hyponatremia). Toxicology quantifies this principle through the dose-response relationship—the mathematical function relating the amount of a substance received (dose) to the magnitude of the biological effect (response). A dose-response curve typically shows a threshold below which no adverse effect occurs, followed by a rising curve of increasing severity. The LD50 (lethal dose for 50% of a test population) is the most common measure of acute toxicity: table salt has an LD50 of 3,000 mg/kg in rats, while botulinum toxin has an LD50 of 0.001 mg/kg—a three-million-fold difference.