Caffeine

Getting that jolt, of course, is why many of the most popular beverages on Earth—coffee, cola, tea—just happen to contain caffeine. Whether it's a graduate student downing mocha in the lab or a monk sipping green tea while chanting in the temple, mankind's favorite stimulant is at work every day, all over the world.

And every night as well.

https://www.nationalgeographic.com/science/health-and-human-body/human-body/caffeine-buzz/