What does a dosage tell you about a chemical?

In the 16th century, Paracelsus, Theophrastus von Hohenheim, famously said that...........$\text{the dose determines the poison}$, still a fundamental principle of toxicology/pharmacology.
$\text{(Sola dosis facit venenum: Only the dose makes the poison")} .$
Which in other words is....$\text{the dose determines the poison}$.
And thus a chemical, a medication, that is $\text{more effective}$, may be administered at a LOWER dose. Administration of higher doses may lead to side effects and injury. A modern toxicologist could not refute this statement. And when a new drug is marketed for a specific condition, some unlittle effort would be placed on establishing a dose-response curve aimed at the discovery of the minimum dose for the maximum response, and an estimate of the dosage that would cause side effects and injury.