Many people can drink coffee without sleep trouble but stay awake all night after half a cup of milk tea. Scientific researches prove tea drinks contain both caffeine and theophylline, two distinct methylxanthine alkaloids with different chemical structures and physiological functions. Caffeine features stronger central nerve stimulation while theophylline works more on heart, bronchi and urination, with respective half-lives of 3-5 hours and 4-6 hours. A 2024 national sampling test by China CDC found a standard 500ml milk tea contains 134.2mg caffeine on average, and oolong-based milk tea has 56.1mg theophylline. Shops boil tea at high heat for long hours to extract over 90% active ingredients; milk protein delays gastrointestinal absorption and added sugar amplifies excitatory effects, extending stimulating duration greatly. Around 15%-20% of people have low enzyme activity to metabolize theophylline and are highly sensitive to milk tea. Health experts suggest avoiding tea-based beverages after 3 p.m., and healthy adults should limit daily caffeine intake under 400mg.
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