According to Paracelsus, what determines whether a substance is a poison?

Paracelsus, a pioneering figure in toxicology, famously stated, "The dose makes the poison," which underscores the foundational principle that the toxicity of a substance is largely determined by the amount administered rather than the substance itself. This concept highlights that even benign compounds can be harmful or toxic if consumed in sufficiently high amounts.

For example, water is essential for life, but in excessive quantities, it can lead to water intoxication and serious health consequences. Conversely, many substances considered toxic can be safely used in small quantities. This principle emphasizes the critical role of dosage in assessing the potential harm of any substance, making it the core aspect in determining whether something acts as a poison.

The other options, while relevant to the overall study of toxicology, do not encompass the general rule established by Paracelsus. The chemical composition may indicate potential toxicity, but it is the dosage that truly determines the outcome. Similarly, the route of administration and the method of synthesis can influence the effect of a substance, but they do not serve as the definitive factor in determining toxicity. Thus, dosage remains the key element in distinguishing a poison from a non-poisonous substance according to Paracelsus' principle.