Dose–response relationship

A dose–response relationship describes how the frequency or severity of an effect changes with the amount of exposure to a substance, agent, or intervention.

Threshold dose: The exposure level below which a specified effect is not observed or expected under a model. A threshold marks where the measured effect begins to rise above baseline.
Dose: The amount of a substance administered to or received by an organism, often expressed relative to body mass. Dose is the exposure quantity plotted against an effect in many relationships.
Reference dose: An estimate of daily human exposure likely to pose negligible risk of harmful effects over a lifetime. Regulators derive it from dose–response evidence, typically applying uncertainty factors.
Linear no-threshold model: A model assuming risk increases linearly with dose and has no safe threshold, including at low doses. It is one policy-relevant interpretation of dose–response data when low-dose effects are uncertain.
No-observed-adverse-effect level: The highest tested exposure at which a study detects no adverse effect compared with controls. This study-derived point is often used when estimating a threshold for harm.
Exposure assessment: The estimation of how much of an agent reaches people, populations, or environmental receptors over time. Actual exposure may differ from the administered dose used in a study.
Benchmark dose: A dose estimated to produce a predefined change in response, calculated by fitting a dose–response model. It uses the curve itself to estimate a point of departure for risk assessment.
Threshold model: A model in which an effect occurs only after exposure exceeds a defined dose. It differs from no-threshold models by treating sufficiently low exposure as effect-free.
Hormesis: A biphasic response in which low exposure stimulates an effect while higher exposure inhibits it. It contradicts the assumption that effects always increase in one direction with dose.
Adverse effect: A harmful or undesirable change in health or function caused by an exposure or intervention. The chosen adverse outcome determines what response the relationship measures.

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