Caffeine: Your Frenemy

Caffeine is the world's most widely used psychoactive substance and a genuine cognitive enhancer, when used strategically. It blocks adenosine receptors, stopping drowsiness signals from reaching your brain.

The strategic approach: drink caffeine 90 minutes after waking and set a hard cutoff of 2 PM (or 8-10 hours before bedtime). Stay at moderate doses of 200-400 mg a day, roughly 2-4 cups of coffee.