L-Theanine 5-N-ethylglutamine is a unique free-form amino acid found in green tea.  L-Theanine is the predominant amino acid in green tea and makes up 50% of the total free amino acids in the plant. L-Theanine is a relaxant that increases alpha-waves producing mental and physical relaxation decreasing stress and anxiety, without inducing drowsiness. L-Theanine is a building block for gamma amino butyric acid GABA . GABA blocks the release of the neurotransmitters dopamine and serotonin, playing a key role in the relaxation effect. 
In addition to its relaxing, calming and focusing qualities, L-Theanine may also help with the following
Increases dopamine levels improving concentration & learning ability.
  Eases the side effects of too much caffeine.
  Controlling hypertension by lowering blood pressure.
  Diminishing symptoms of PMS.
  Supports the Immune System by lowering cortisol
L-Theanine is a feel good supplement that causes no adverse reactions. It wont make you drowsy or groggy. L-Theanine is considered to be safe based on its historical use as a part of tea.  A heavy tea drinker 6-8 cups a day will consume between 200 to 400 mgs of L-Theanine daily. One 200mg capsule of L-Theanine, or as needed depending on stress and anxiety levels, is the recommended dosage. L-Theanine can be taken with food or on an empty stomach.  Some people open the capsule and add to their coffee or tea. L-Theanine is neutral in taste and tends to take the bitterness out of coffee or tea. L-Theanine may enhance the anti-tumor effects of some chemotherapy drugs. Use of L-Theanine with chemotherapy agents must be done under strict medical supervision.