What does the phrase 'The dose makes the poison' mean?

• A. Any substance can be toxic if taken in a sufficient quantity; toxicity is dependent on the dose rather than the substance itself.
• B. The substance determines the toxicity regardless of dose.
• C. Toxicity is always the same for any substance.
• D. Only toxins have dose-response relationships.

Answer: (A)

Toxic effects depend on how much you are exposed to. The idea is that the amount of a substance determines whether it will harm you, not just the substance itself. A small exposure to almost any chemical is unlikely to cause harm, while a larger exposure can be toxic. The same substance can be therapeutic at a proper dose (like a medicine) and toxic at too high a dose. Potency varies by substance, and factors such as how you take it, how long you’re exposed, and your individual sensitivity can influence the outcome, but the key point is the dose–response relationship: harm rises with dose. Statements that say toxicity is determined solely by the substance, or that toxicity is the same for all substances, or that only toxins have dose–response curves, miss this fundamental idea.