The Half-Life Problem
Caffeine has a half-life of ~5 hours. That 4pm cold brew? 25% of it is still in your system when you try to sleep at midnight.
I conducted an N=1 experiment.
- Phase 1: Caffeine ad-libitum until 4 PM.
- Phase 2: Zero caffeine after 11 AM.
The Results
My Sleep Latency (time to fall asleep) dropped from an average of 42 minutes to 8 minutes. This directly impacted my recovery score (see Deep Sleep vs Deep Work).
Take Control: Don't guess your sensitivity. Connect your data to see exactly when your last coffee should be.
But the scarier metric was Resting Heart Rate (RHR). My average nightly RHR dropped by 4 BPM in Phase 2. That is thousands of saved heartbeats per night. Less stress. More recovery.
The Rule
No caffeine within 10 hours of sleep. Non-negotiable.
If you need energy in the afternoon, your metabolic engine is broken. Fix your insulin sensitivity, don't patch it with stimulants. For the ADHD brain, consistency is key—read about Why Streaks Kill Motivation.