epistemic status: confident in the overall picture, substantial quantitative uncertainty about the relative potency of caffeine and paraxanthine

tldr: The effects of caffeine consumption last longer than many assume. Paraxanthine is sort of like caffeine that behaves the way many mistakenly believe caffeine behaves.

You've probably heard that caffeine exerts its psychostimulatory effects by blocking adenosine receptors. That matches my understanding, having dug into this. I'd also guess that, insofar as you've thought about the duration of caffeine's effects, you've thought of them as decaying with a ~5 hour half-life. I used to think this, and every effect duration calculator I've seen assumes it (even this fancy one based on a complicated model that includes circadian effects). But this part is probably wrong.

Very little circulating caffeine is directly excreted.[1] Instead, it's converted (metabolized) into other similar molecules (primary metabolites), which themselves undergo further steps of metabolism (into secondary, tertiary, etc. metabolites) before reaching a form where they're efficiently excreted.

Importantly, the primary metabolites also block adenosine receptors. In particular, more than 80% of circulating caffeine is metabolized into paraxanthine, which has a comparable[2] binding affinity at adenosine receptors to caffeine itself. Paraxanthine then has its own [...]

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Outline:

(02:43) Paraxanthine supplements

(05:13) Exactly how potent is paraxanthine compared to caffeine?

(08:41) Concluding thoughts

The original text contained 9 footnotes which were omitted from this narration.

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First published:
April 8th, 2026

Source:
https://www.lesswrong.com/posts/vefsxkGWkEMmDcZ7v/the-effects-of-caffeine-consumption-do-not-decay-with-a-5

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Narrated by TYPE III AUDIO.

“The effects of caffeine consumption do not decay with a ~5 hour half-life” by kman

LessWrong (30+ Karma)

“The effects of caffeine consumption do not decay with a ~5 hour half-life” by kman