A dose is a quantity of something (chemical, physical, or biological) that may impact an organism biologically; the greater the quantity, the larger the dose. In nutrition, the term is usually applied to how much of a specific nutrient is in a person’s diet or in a particular food, meal, or dietary supplement. In medicine, the term is usually applied to the quantity of a drug or other agent administered for therapeutic purposes. In toxicology dose may refer to the amount of a harmful agent (such as a poison, carcinogen, mutagen, or teratogen), to which an organism is exposed. Chemicals are the most common things for which doses are measured, but there are others, such as radiation exposure. For humans, most doses of micronutrients and medications are measured in milligrams (mg), but some are measured in micrograms because of their potency. Nonmedicinal poisons span the measurement scale; some poisons are so dangerous that a single microgram of it could be deadly, whereas other substances take much more. For example, even water is toxic when consumed in large enough quantities.