Duration of action

Duration of action refers to the window of time during which a substance produces a pharmacologically measurable effect — the span from when effects become perceptible to when they fall below a meaningful threshold.

This is distinct from a substance's half-life (the time for plasma concentration to halve) and its detection window (how long it remains traceable in urine, blood, or hair). A substance can be detectable for days or weeks after its psychoactive effects have ended.

Duration is not a fixed property of a substance alone. It varies with dose, route of administration, individual metabolism, and whether the substance produces active metabolites.

How it works · its role

Effects last as long as a substance maintains sufficient concentration at its target — a receptor, enzyme, or transporter — to drive a response. Once levels fall below that threshold, the effect ends, even if the substance is still present elsewhere in the body.

Route of administration shapes duration significantly. Inhaled or intravenously administered substances reach peak concentration quickly but may also clear faster; oral administration tends to produce a slower, more sustained curve because absorption through the gut is gradual.

Active metabolites can extend duration substantially. When the body converts a substance into a compound that is itself pharmacologically active, the effective duration reflects both the parent compound and the metabolite. Some substances are inactive until metabolised — so-called prodrugs — and their duration depends almost entirely on that conversion step.

Enzymes, particularly the cytochrome P450 family, govern how quickly most substances are processed. Genetic variation, age, liver function, and competing substances all influence enzyme activity — and therefore how long effects last in a given person.

Relevance to substances & effects

Duration shapes the character of an experience as much as peak intensity does. A substance with a short, sharp duration demands different preparation and context than one whose effects extend across most of a day.

Classic psychedelics illustrate the range well. Smoked DMT produces intense effects lasting roughly fifteen to thirty minutes, while LSD can remain active for eight to twelve hours or more. Psilocybin-containing mushrooms typically produce effects over four to six hours, partly because psilocybin is converted to psilocin in the body, and psilocin then clears at a moderate rate.

Benzodiazepines span an even wider range — from short-acting compounds whose effects resolve within a few hours, to long-acting ones whose half-lives and active metabolites extend activity for days. This variation has direct implications for residual impairment and the risk of accumulation with repeated use.

Route of administration creates significant differences within the same substance. Cannabis inhaled typically produces effects that resolve within one to three hours; taken orally, first-pass metabolism converts THC to an active metabolite with a longer duration, and effects can persist for four to eight hours or more.

For substances where duration affects dose timing or interaction risk, understanding duration of action is central to interpreting any safety guidance on these pages.