Caffeine might stick around longer than the 5‑hour half‑life everyone cites

A fresh analysis on LessWrong argues a simple half‑life story for caffeine is misleading. The post’s author says they are “confident in the overall picture” but admits substantial quantitative uncertainty about how potent caffeine’s main metabolite, paraxanthine, really is. The punchline: much of the stimulant effect attributed to “caffeine” after a cup of coffee may actually come from paraxanthine, a metabolite that keeps adenosine receptors blocked long after the parent molecule has declined.

How the chemistry stretches the effect

Caffeine is mostly not excreted intact. Instead it’s metabolized, and more than 80% of circulating caffeine becomes paraxanthine — which, crucially, also binds adenosine receptors. Paraxanthine has its own 3–5 hour half‑life, and because you get a cascade (Caffeine → Paraxanthine → elimination), the combined “effective concentration” curve is broader and declines slower than a single‑compound model predicts. In the author’s simplified simulator (100 mg ingestion modeled), the time to fall to half of peak effective concentration is roughly twice what a plain 5‑hour caffeine half‑life would suggest, assuming paraxanthine is equipotent. That assumption is uncertain — the author notes a possible fourfold window of relative potency — but the qualitative result stands: effects last longer than standard calculators imply.

Paraxanthine supplements and early impressions

It has been reported that paraxanthine began appearing as a direct supplement in the US around 2022, and that many products use an enfinity‑branded form, allegedly due to broad patents. On vendor pages, paraxanthine is marketed as “cleaner,” possibly safer, and less influenced by slow caffeine metabolism — claims the LessWrong poster flags as manufacturer messaging rather than settled science. The poster also reports having tried intermittent 100 mg doses themselves and links to a simulator you can tweak to explore potency assumptions. Anecdotes are fun, but remember: controlled human pharmacology beats vibes and capsule selfies.

Why this matters (and what to watch)

So what? If the model is right, we've been underestimating how long adenosine blockade — and therefore stimulant effects, sleep disruption, or tolerance formation — can hang on after a dose. That’s a small but meaningful chance to rethink common advice about “cutoff times” for caffeine before bed, and it raises interesting questions for nootropics and supplement markets: would taking paraxanthine directly give you a different, perhaps more predictable ride? Worth asking next time you reach for a late‑afternoon cup — or a capsule.

Sources: lesswrong.com, Hacker News