Potency
pharmacologyThe amount of a substance needed to produce a given effect: a more potent compound reaches that effect at a smaller amount than a less potent one. Potency describes only the amount required, not the character of the effect or its ceiling, which is why a highly potent compound is not thereby a stronger experience — only one in which small differences in amount matter more.
Potency describes where a drug sits on the dose-response curve — specifically, how little of it is needed to reach a given level of effect. It is a property of the drug-receptor relationship, not of the subjective experience that relationship ultimately produces.
The term is frequently conflated with efficacy, which is something different: the maximum effect a drug can produce, regardless of dose. A highly potent compound may still have a low ceiling; a low-potency compound may, at high enough doses, produce a more intense effect. Keeping the two ideas separate is essential for reading dose tables accurately.
How it works · its role
Potency is quantified through the EC₅₀ — the concentration that produces half of a drug's maximum response in a cellular or tissue system — or the ED₅₀, the effective dose in fifty percent of subjects in a study. The lower the EC₅₀, the greater the potency: less of the compound is needed to engage the target.
Binding affinity — how tightly a molecule attaches to its receptor — is the primary driver of potency at the molecular level. Absorption, distribution, and metabolism further shape it at the whole-organism level.
High potency narrows the therapeutic window: the gap between the dose that produces a desired effect and the dose that produces harm. Small measurement errors that matter little with a low-potency compound can be significant when the effective dose is measured in micrograms.
Relevance to substances & effects
Potency comparisons appear throughout the substance encyclopedia when contrasting compounds in the same class. Fentanyl, for example, is substantially more potent than morphine as an opioid agonist — a smaller mass reaches the same degree of receptor activation. This is a statement about dose, not experience: it matters primarily because it shrinks the margin between an effective dose and a dangerous one.
Serotonergic psychedelics illustrate the other end of the range. LSD is active at microgram quantities; psilocin, the active form of psilocybin, is effective at milligram quantities. By pharmacological measure LSD is far more potent, though both can produce comparable depth of effect at their respective doses.
When a dose table lists a substance in micrograms rather than milligrams, it is signaling high potency — and with it, heightened sensitivity to measurement precision.
AI-generated · not yet verified by a human reviewer
Harm-reduction reference — not medical advice.