Adenosine

Adenosine is a key molecule involved in sleep regulation, and its levels build up in the nervous system the longer we are awake. This build-up creates a drive for sleep, which is sometimes described as sleep hunger or sleepiness. The process of sleep effectively clears adenosine from the system, particularly during non-REM sleep. Essentially, sleep acts as a reset, reducing adenosine levels and alleviating the sleep drive 1.

Caffeine interacts with adenosine by blocking its receptors. When caffeine occupies these receptors, adenosine cannot bind to them, which temporarily prevents the feeling of sleepiness that adenosine would normally induce. This blockade is why caffeine is effective at making people feel more alert. Over time, as the effects of caffeine wear off, the adenosine that has continued to accumulate can bind to its receptors again, often resulting in a feeling of tiredness or a "crash" 1 2.

Moreover, Andrew Huberman mentions that certain conditions, like viewing morning sunlight and engaging in brief, intense exercise, might also influence adenosine levels or its effects, suggesting a complex interplay between various physiological factors and adenosine's role in sleep and wakefulness 3.