The wisdom of tradition.
Proven by science.

Chinese materia medica recorded caffeine's central effect over a thousand years before anyone named the molecule. The Bencao Gangmu's tea entry, citing the ancient Shennong Shijing, says tea "makes one sleep less, gives strength and lifts the mind," and Tao Hongjing notes a roasted tea from Badong "keeps one from sleeping". Chen Cangqi, writing in 739, warned that long-term use "makes one unable to sleep" and urged drinking it hot rather than cold. Li Shizhen's own summary in this 1596 compilation praises the same effect: tea "clears the spirit... so that one is neither dull nor sleepy." A Tang-era preface he quotes captures the trade-off bluntly: "the benefit is a good day, the cost a lifelong drain."

What the science saysTea keeping people awake is caffeine's best-documented effect: a 2023 meta-analysis of 24 studies found it cut total sleep by 45 minutes and sleep efficiency by 7%, while shortening deep sleep, and 400 mg still disrupted sleep 6 hours before bed.