Caffeine

Caffeine boosts alertness, energy, and motivation by blocking adenosine’s sleepiness signal and influencing dopamine, acetylcholine, and adrenaline; the trade-off is that it can disrupt sleep. 1 2 3

• About 90% of adults worldwide: Consume a caffeinated beverage daily, making caffeine the world’s most popular drug. 4
• Caffeine crash: When caffeine wears off and leaves adenosine receptors available again, accumulated adenosine can bind and make you feel especially sleepy. 5
• Reinforcement and mood: Caffeine can condition preferences for the flavors and settings associated with its effects, and regular use can increase the number and efficacy of dopamine receptors. 6 It is also associated in the discussion of withdrawal with mild depression, but the cited passage does not establish that caffeine lowers depression rates. 7
• Dopamine and visual focus: Caffeine can increase dopamine-receptor density and efficacy; its adrenaline-related arousal can also dilate pupils and make the visual field more tunnel-like. 8 9
• Timing and moderation: Keep caffeine early enough to protect sleep—Huberman recommends avoiding it within 8–12 hours of bedtime—and choose an amount that suits your tolerance. 10