Definition
The time required for the concentration of a drug or substance in the body to be reduced by one-half through normal metabolic and elimination processes.
Plain English
How long it takes the body to get rid of half of a drug that is in your system. After one half-life, half of the dose is still working in you. After another half-life, half of that is still there, and so on.
Context Anchor
Seen in aviation medical and drug discussions when judging how long a medication or other drug may continue to affect a pilot.
Derivation
From 'half' plus 'life,' meaning the length of 'life' a substance has in the body before half of it is gone. The term was originally used in physics for radioactive decay and was later adopted by pharmacology to describe how long drugs persist in the body.
Why Pilots Care
Pilots must know a drug's half-life to determine safe return-to-flight times and avoid impairment from lingering effects.
Analogy
Think of a tank that drains by half every hour. After one hour it is not empty; it still has half left. After another hour it still has a quarter of the original amount left.
Grounding Statement
Half-life is about how much of the drug remains in the body over time, not just whether the pilot still feels its effects.
Intuition Check
Half-life does not mean the drug is gone after that amount of time. It means only half of the remaining drug has been reduced.
Example Sentence 1
Because the antihistamine she took had a 12-hour half-life, she grounded herself for the rest of the day rather than risk flying impaired.
Example Sentence 2
A drug with a short half-life clears faster than one with a long half-life, affecting when a pilot can resume flying duties.