Half-Life (Elimination)
Also known as: elimination half-life, drug half-life, t1/2
Verified from StatPearls on 06-02-2026Elimination half-life is a pharmacokinetic measure used to describe how quickly a drug is cleared from the body. It supports calculations around dosing intervals, steady-state concentrations, and excretion patterns. The verbatim definition below, drawn from the National Library of Medicine (NCBI Bookshelf), outlines the underlying principle and notes the distinction between first-order and zero-order elimination.
MedivaScan summary. The authoritative source quote follows below.StatPearls definition
In medical science, the term half-life typically refers to the elimination half-life. The elimination half-life is defined as the time required for the concentration of a specific substance, typically a drug, to decrease to half of its initial amount in the body. Understanding the concept of half-life is essential for determining excretion rates and steady-state concentrations of any specific drug. Although different drugs have varying half-lives, they all share a common principle—after one half-life, 50% of the initial drug amount is removed from the body. The characteristic decline of drug concentrations over time has long been studied in the field of pharmacokinetics and can be described using basic differential equations. Most clinically relevant drugs follow first-order pharmacokinetics, meaning their drug-elimination rates are directly proportional to plasma concentrations. In contrast, a few drugs follow zero-order elimination, in which the drug amount decreases by a constant amount over time, regardless of initial concentration, for example, ethanol. This activity focuses on first-order half-life elimination as it is the most frequently encountered in clinical practice.
National Library of Medicine (NCBI Bookshelf)View on source ›Verbatim quote. Last verified 06-02-2026.