Half-life vs duration of action
Explains why how long you feel a drug doesn't match its blood half-life — and the four reasons the two come apart.
Where this fitsConnects to 3 · Unlocks 1
- Connects to
- Half-life and redistribution — Half-life and redistribution come from pharmacokinetics.
- How drugs bind: affinity, shape and binding site — Irreversible and very tight binding stretch effects beyond the half-life.
- Indirect agonists: reuptake inhibitors, enzyme inhibitors and releasers — Releasers depend on stored neurotransmitter, which can run out.
- Unlocks
- Safety: therapeutic index, dosing across species, allergy and polypharmacy — Duration mismatches matter for overdose reversal and polypharmacy.
Orient
Half-life specifically refers to levels of the drug in the bloodstream. This relates to the duration of the psychoactive effect of the drug – but not exactly: brain vs. blood concentration and the redistribution period, irreversible binding, very tight binding, and effects that depend on stored endogenous NT all pull the two apart.
Course terms
Your professor's wording, word for word from the slides. Learn the term and this definition — the explanation underneath is only there to help it make sense.
- Half-life
“Half-life specifically refers to levels of the drug in the bloodstream”Slides 05, p. 40
Not the same as how long you feel it.
- Duration of action
“This relates to the duration of the psychoactive effect of the drug – but not exactly”Slides 05, p. 40
Four reasons they differ, each with a course example (THC, MAOIs, LSD, MDMA).
- Redistribution period
“Redistribution period (first couple hours)”Slides 05, p. 41
THC sticks around in fatty tissues and returns slowly to the bloodstream.
From your course: Course slides 05, pp. 40–41
Tip: the ← and → keys move through the lesson.
Full lesson: Half-life and redistribution