Lecture #1 october 31, 2012 toxicant: any substance that causes an adverse biological effect (toxic response) toxicosis: chemically caused disease; toxic response; poisoning. Drug: substance that can have pharmalogical effects or toxic effects. All substances, natural or man-made, are poisons (toxicants) if the right dose is given. Every toxicant has a threshold dose. threshold dose: dose below which no adverse effect occurs: factors: response being measured (acute vs. chronic) Due to genetic variability, not every indivudal is affected the same way by a given dose of a given substance. Toxic response increases with increased dose (graded response). individuals: dose = effect, symptom severity, death. Populations: number affected individuals exceptions: immunological reactions. Dose refers only to a weight of substance that should be taken. Dosage refers to the dose per body weight. stimulation of biological systes at low doses, inhibition at high doses.