Why can tea make you feel sleepy ?
Other people that have answered this question are missing the most simple and important explanation.
In fact, tea (and any Yang stimulant) makes you sleepy for the same reason exercising makes you sleepy.
That is why tea, coffee, cacao and other stimulants, are called “exercise-mimetics”. They simulate a state of high activity in your body. So, naturally, after stimulation, the body gets tired in order to recover. It is a simple as that.
If you take tea in a moment when your body already needs sleep, it will make you feel sleepy almost immediately because there is no much energy left to wake up. By taking tea, you simply accelerate the natural shift from Yang (stimulation, activity) to Yin (recovery, sleep, relaxation).
When you are already tired, that shift can happen so rapidly that it makes you think tea is directly inducing sleep. But that phenomenon is alway indirect: it is still through Yang stimulation (mainly), that tea makes you sleepy.
Maybe you have noticed that it works also the other way. In fact, some foods and compounds stimulate Yin mechanisms (instead of Yang). But if you have already a natural abundance of energy, these Yin substances will accelerate the shift from Yin to Yang, acting like a coffee instead of inducing sleep. Lily bulb and Rehmannia are examples of these Yin substances that can give you more energy by making you feel more tired temporarily.
However, if Yang-Yin communication does not operate well in your body, the induced tiredness will be expressed as anxiety or other symptoms related to poor homeostasis.
Cheers !
