There’s something calming about sipping a cup of green tea, and it may be the L-theanine. An amino acid found naturally in green tea and some mushrooms, L-theanine is said to alleviate anxiety, improve sleep, and reduce stress.

Health Benefits

To date, scientists have yet to extensively explore the benefits of L-theanine. However, preliminary research suggests it may help lift mood and calm the body’s response to stress and anxiety.


L-theanine may help to increase adaptability to stress, according to a 2016 study.1 Healthy participants consumed a drink containing 200 milligrams (mg) of L-theanine or a placebo. One hour after consumption, the stress response to a cognitive stressor was significantly reduced in those who consumed the L-theanine drink. Three hours after consumption, saliva cortisol (a hormone secreted in response to stress) was significantly lower.

Another study explored the effects of regular consumption of L-theanine and found that daily intake decreased subjective stress and saliva levels of α-amylase (an enzyme released in response to stress) in undergraduate students undergoing stress.2


Salivary α-amylase activity is a marker of overall sympathetic nervous system activity implicated in both stress and sleep. The study in undergraduate students also found that higher levels of α-amylase were correlated with shorter sleeping time.

Another study examined the effects of a low-caffeine green tea on sleep quality and found that saliva α-amylase levels were significantly lower in those who drank the low-caffeine green tea after seven days of daily intake than in those who consumed the standard green tea.3 Higher sleep quality was higher in those who had consumed a larger amount of low-caffeine green tea containing L-theanine.


A 2017 study published in Acta Neuropsychiatrica explored the use of L-theanine for major depression.4 The trial included 20 men and women who had 250 mg of L-theanine added to their current medication for eight weeks. They found it had multiple benefits in relieving anxiety, sleep disturbances, and cognitive impairment associated with depression.