The three stimulants in tea have calming and soothing effects, yet keep you alert:
Theophylline relaxes smooth muscles, increases blood flow, and has anti-inflammatory effects.
Theobromine is a mild diuretic. it also helps to relax your muscles and the nerves in the veins so the blood flows easily.
L-Theanine is an amino acid that reduces mental and physical stress. Combined with caffeine it increases attention, working memory, and focus.