why shouldn't we have coffee right after we wake up

Delaying caffeine intake for 90 to 120 minutes after waking is recommended to help prevent energy crashes and improve overall alertness throughout the day. When you wake up, your cortisol levels naturally rise, contributing to wakefulness. If you consume caffeine immediately, it can interfere with the natural adenosine clearance process and cortisol increase, both of which are essential for maintaining energy levels and alertness without dependency on caffeine.

By delaying caffeine intake, you allow your body to naturally reach its cortisol peak and clear adenosine, which helps sustain energy levels throughout the morning and reduces the likelihood of an afternoon energy crash. Consuming caffeine early can create a cycle of dependency, potentially leading to more caffeine consumption later in the day, which can disrupt sleep quality [1] [2] [3].