Toxicology is largely a subset of Pharmacology and is sometimes defined as Overdose Pharmacology.
The rules of causation are possibly more elegant in pharmacology than in any other science. is the study of how drugs act, from the submicroscopic molecular level to statistical investigations of the effects of drugs on populations of people - pharmacoepidemiology.
Life scientists, unlike physicians not engaged in research, systematically quantitate results for statistical significance. It is second nature to be familiar with chance associations and the unbiquitous 'noise' that can obscure or occasionally mimic true signals.
In another sense, causation by a drug is typically quantitative in terms of the dose or concentration of drug required to cause an efffect.
A Pharmacologist is a scientist. A physician uses drugs and diagnoses diseases using principles of pharmacology. But it is the scientist who discovers how drugs cause their actions; it is the pharmacologist who quantitates causation by analyzing the dose-response for therapeutic and toxic effects.