Half-life vs duration
People often use “half-life” as shorthand for “how long a drug lasts.” They are not the same concept. Half-life is a pharmacokinetic measurement about how quickly a concentration decreases. Duration is a subjective and pharmacodynamic outcome.
Why effects can end before elimination
- Concentration thresholds: effects can fade once concentration falls below a personal threshold even though the substance is still present.
- Tolerance and adaptation: the same concentration can produce different effects over time or across individuals.
- Route and absorption: fast absorption can create a high peak and a shorter-feeling experience even if elimination is slow.
Why effects can outlast the parent compound
- Active metabolites: some substances are converted into other compounds that have their own kinetics and effects.
- Downstream biology: some effects involve signaling cascades that continue after concentration drops.
- Sleep and circadian factors: perception of duration can be shaped by when the experience happens.
How HalfLifeDB uses half-life
HalfLifeDB uses one half-life number to illustrate exponential decay. It is best used to compare “short” vs “long” half-lives and to understand why repeated dosing can cause overlap.
HalfLifeDB does not estimate impairment, safety, or subjective experience. See the disclaimer for limitations.