At the end of 12th century the Zen monk Yosai (1141-1215) brought home Zen Buddhism and, as part of this, the new way of producing and drinking tea. The way of drinking tea that Yosai brought back is very much like today's custom of whisking powdered green tea before drinking it.
In Kempo 2 (1214), when Shogun Minamoto no Sanetomo (1192-1219) was suffering from a hangover, Yosai prepared tea for him and Sanetomo completely recovered from the hangover. This story is recorded in 'Azuma kagami'. At this time Yosai gave the Shogun a book explaining the effects of tea, 'Kissa Yojoki'[Drinking tea for health]. In this it says that tea is an elixir that strengthens the internal organs and lengthens life. There are many medicinal effects mentioned in the book that have been proved to be true in the present world of medicine. After this, tea spread widely throughout Japan and the culture of drinking tea took root.