The Claim
Popularised by neuroscientist Andrew Huberman, the "90-minute delay" theory suggests you should wait 90 minutes after waking before consuming caffeine, to allow cortisol to peak naturally and avoid afternoon crashes.
The Science
Cortisol does peak in the first hour after waking — this is the Cortisol Awakening Response (CAR). Caffeine works partly by blocking adenosine receptors, but adenosine doesn't accumulate significantly in the first 60–90 minutes of wakefulness anyway.
The crash argument is more supported: drinking coffee while cortisol is already high may blunt the cortisol response and cause your body to rely more heavily on caffeine, potentially worsening afternoon fatigue.
Practical Guidance
A 60–90 minute delay is a reasonable, low-cost intervention worth trying — especially if you currently feel groggy despite coffee or experience mid-afternoon crashes. Use our Caffeine Timing Calculator to build your optimal window.
The delay matters less than the cutoff: consuming caffeine within 8–10 hours of your target sleep time is the higher-impact variable for most people.