All things are poison, and nothing is without poison; but the dose makes it clear that a thing is not a poison.

[Alle Ding sind Gift und nichts ohn’ Gift; allein die Dosis macht, daß ein Ding kein Gift ist.]

Philippus Aureolus Paracelsus (1493-1541) German alchemist and physician [Bombast von Hohenheim]

“The Third Defense in Writing New Prescriptions [Die dritte Defension wegen des Schreibens der neuen Rezepte], Seven Defenses [Septem Defensiones] (1538)

As quoted in F. Geerk, Paracelsus: Arzt unserer Zeit [Paracelsus: Doctor of Our Time] (1992). Variants:

• "All drugs are poisons; the benefit depends on the dosage."
• "All substances are poisons; there is none which is not a poison. The right dose differentiates a poison and a remedy."

This is frequently (and misleadingly) paraphrased: "Everything is a drug; it depends on the dose."