Dose

A dose is the amount of a substance administered to a person or animal. It is typically described by mass (milligrams or grams), volume (milliliters), or activity for radioactive materials, and may be scaled to body size (for example, milligrams per kilogram). The administered dose interacts with the drug's formulation and route and is distinct from the dosing regimen, which specifies how often and for how long the substance is given.

In pharmacology, the dose is selected to achieve a therapeutic effect while minimizing adverse effects. The minimum effective dose is the smallest amount that produces the desired effect; the maximum tolerated dose is the highest amount that does not cause unacceptable toxicity. The therapeutic window is the range between these values. A dose-response relationship describes how increasing doses produce increasing effects up to a plateau, and pharmacodynamics may consider potency and efficacy.

Pharmacokinetics describes the fate of the dose: absorption into the bloodstream, distribution to tissues, metabolism, and excretion. Bioavailability measures the fraction that reaches circulation, with oral dosing often affected by first-pass metabolism. The dose, together with the dosing interval and the drug's half-life, determines steady-state concentrations and accumulation with repeated dosing.

Several factors influence dosing, including age, weight, organ function, genetic factors, other medications, and disease. Pediatric and renal/hepatic impairment require adjustments. Safety monitoring is essential to detect underdosing or overdosing and to adjust the plan accordingly.

In radiology and radiation protection, dose can also refer to the absorbed dose, measured in gray, or the effective dose, measured in sievert, used to estimate risk from ionizing radiation.