"Experiment personally to find your caffeine cutoff Because adenosine receptors vary genetically across individuals, caffeine's effect on sleep differs dramatically from person to person — some people cannot tolerate any caffeine past 11 a.m. without disrupting sleep, while others can drink it at 4 or 5 p.m. and fall asleep fine. Huberman notes, "there's a small subset of people that can drink caffeine until very late and they have no trouble falling asleep because they actually have a mutant form of the adenosine receptor." Rather than following a universal rule, the actionable takeaway is to run a personal experiment: gradually move your last caffeine dose earlier or later and track its effect on your sleep quality over one to two weeks. Source: Andrew Huberman, Huberman Lab, Master Your Sleep & Be More Alert When Awake"