https://lfbiohacking.squarespace.com/blog/an-evidence-based-guide-on-reversing-caffeine-tolerance

“Conclusion/TL;DR

Complete tolerance to caffeine’s subjective effects is complete and takes at least 2 weeks at 400mg/day to develop. Caffeine’s performance-enhancing effects remain for at least 20 days at 210mg/day. Tolerance to caffeine’s effects on cerebral blood flow, blood pressure, and cortisol is incomplete. Tolerance takes 2 days to reverse at 100mg/day and up to 9+ days at 400mg+/day. Caffeine intake exhibits preventative effects on the development of Parkinson’s, Alzheimer’s, and depression, but also increases the risk of developing anxiety and Huntington’s.”