Toxicology is the science of poisons: what makes a substance harmful, how it gets into the body, what damage it does, how much is too much, and what can be done about it. It sits between chemistry, biology, and medicine. Three settings matter most. In forensic toxicology, scientists test a dead or living person's blood and tissue for drugs, alcohol, or poison — this is where the common phrase 'toxicology report' comes from, and after a sudden death people often wait weeks for the toxicology results. In clinical toxicology, doctors treat people who have taken too much of something. In regulatory toxicology, scientists decide what level of a chemical is safe in food, water, medicine, or a factory. The idea at the centre of the subject is dose: toxicology does not divide the world into poisons and non-poisons, but asks how much of a substance, taken how, over how long, causes harm. That is why toxicologists like the old saying that the dose makes the poison. It is a technical word, but it is common in news reports, so learners meet it more often than most science words.