Active dose

Active dose is the smallest quantity of a substance, delivered by a specific route of administration, that produces its characteristic effects. Below this threshold the substance may be present in the body but produce no perceptible change; at it, the first effects — however faint — begin to appear.

The figure is not a fixed property of a compound. It shifts with route: the same substance inhaled or insufflated will typically have a lower active dose than the same substance taken orally, because absorption and first-pass metabolism differ.

It shifts with tolerance: a person who has used a substance repeatedly may no longer respond at the threshold that affects a first-time or drug-naïve user. It shifts between individuals too, sometimes by a factor of several times, driven by differences in body composition, enzyme activity, and receptor sensitivity.

Across substance classes, active doses span orders of magnitude — what constitutes a threshold for one compound would be a large dose of another. This spread is part of why the active dose is a useful reference point: it indicates a substance's potency relative to others in a way that raw effect descriptions alone cannot.

How it is done

In practice, the active dose functions as a reference point in dose tables rather than a guide for self-titration. Published figures are drawn from human pharmacology research, case reports, and harm-reduction databases, and represent an approximate threshold for an unspecified population under standardised conditions.

Awareness of where the active threshold falls — and how far above it a given quantity sits — helps calibrate expectations about onset and whether effects will be perceptible at all. A quantity near the active threshold is the basis for a test dose: beginning close to where effects start in order to assess individual sensitivity before committing to a larger amount.

The figure also anchors the other tiers in a dose table. Common, strong, and heavy ranges are meaningful only in relation to where effects begin. Without the threshold, the other tiers have no reference point.

What it cannot tell you

The active dose identifies where effects begin; it does not indicate what those effects will be, how a specific individual will respond, or whether a given sample contains what it is believed to contain.

Published figures assume the substance is present at the expected concentration. Adulterants, misidentified compounds, and inconsistent preparations mean the true active threshold of an actual sample can differ substantially from the listed figure. A compound more potent than expected will produce effects at a lower quantity; a less pure preparation may not produce perceptible effects at the expected threshold at all.

Knowing that an amount falls at or near the active threshold does not indicate whether the experience will be pleasant, neutral, or distressing. Threshold-level effects can still be disorienting. The active dose marks a floor — the point where something begins — not a measure of what that something will be.