Tolerance

What it is

Tolerance is produced by neuroadaptation. The system that responded to the first dose adjusts to the repeated presence of it, so the same input meets a changed receiver. Two descriptions, escalation and diminishing return, are the same phenomenon seen from either end: escalation is tolerance observed in behaviour, and diminishing return is tolerance observed in experience.

The formal account the vault leans on is Richard Solomon and John Corbit's opponent-process theory of motivation, published in Psychological Review in 1974, in which a compensatory process opposing the initial effect grows with repetition. A second mechanism belongs beside it and is often left out. Shepard Siegel's work from 1975 onwards showed that tolerance is partly learned and tied to context, which is the standard explanation for why a familiar dose taken in an unfamiliar setting is more dangerous than the same dose in the usual one.

In effect

Anna Lembke's Dopamine Nation is where this concept reaches the library, and her clinical cases run the shape at a range of stakes, most sharply in the opioid patients she describes whose pain improved on tapering, which on her account is tolerance and opioid-induced hyperalgesia together. She also uses non-drug examples, reading and then more explicit reading, where the same material stops working and the time spent lengthens.

Two sourcing points are recorded with the concept. Lembke defines tolerance and credits nobody, which is unremarkable for a term this established. More usefully, the word itself is absent from several chapters where the mechanism is doing all the work, so a reader meets the phenomenon repeatedly and the name for it only intermittently, and an unnamed construct cannot be checked. The escalation arithmetic that circulates from that book, a set of dopamine percentages in laboratory animals and the comparison derived from them, is barred by the book's own reliability audit and is not reproduced here.

Where this publication lands: the drug case is robust, and the behavioural extension overlaps heavily with hedonic adaptation and should be labelled as analogy when it is used. Behavioural tolerance in gambling is recognised in the diagnostic manual; for most other behaviours the evidence is thin.

What it does not say

It does not say that any repeated pleasure produces clinical tolerance. The ordinary fading of a new pleasure is hedonic adaptation, and it needs no pharmacology to explain it.

It does not describe or recommend anything anyone should do about a substance, a dose or a schedule. Nothing here is clinical guidance, and anyone with a question about their own use needs a clinician rather than a concept page.

It does not explain addiction on its own. Tolerance is one feature among several, and the accounts that reach for it as a complete explanation are reaching beyond what it supports.

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