What does "half-life" of a drug mean?
Medically reviewed by Drugs.com. Last updated on Oct 11, 2024.
The half-life of a drug is the time it takes for the concentration of the drug in your blood plasma to decrease by half. This measurement helps estimate how long a drug stays in your body and how often doses may be needed.
For example, the half-life of Ambien is about 2 hours. This means that 2 hours after taking Ambien, the concentration of the drug in your bloodstream will be reduced by half. After another 2 hours, it will be reduced by half again, leaving a quarter of the original concentration, and this process continues.
It generally takes about 5.5 half-lives for a drug to be eliminated from the body to the point where it no longer has any clinical effect. For Ambien, it would take around 11 hours (2 hours x 5.5) for it to be mostly cleared from your system.
However, the elimination of a drug varies depending on factors such as age, weight, kidney and liver function, and interactions with other medications. These factors make the half-life an estimate rather than an exact measurement.
For more information, see: Drug Half Life Explained
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