The Health Benefits of L-Theanine

This amino acid may help with anxiety and sleep issues

Green tea pour and assorted loose teas
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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. 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.


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. 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. 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.

Possible Side Effects

To date, little is known about the safety of using L-theanine supplements in the long term. L-theanine is generally considered safe when consumed in green tea. However, the National Institutes of Health (NIH) cautions against drinking more than five cups of green tea daily.

Due to the caffeine content, excessive consumption of green tea may also trigger certain side effects. These may include a headache, insomnia, irritability, diarrhea, and heartburn.

There's also some concern that taking L-theanine in combination with sedatives, lipid-lowering medications, and/or drugs used in chemotherapy may produce harmful effects.

Dietary supplements have not been tested for safety. Because they are largely unregulated, the content of some products may differ from what is specified on the product label.

Keep in mind that the safety of supplements in pregnant women, nursing mothers, children, and those with medical conditions or who are taking medications has not been established.

Dosage and Preparation

Doses as low as 200 mg may be effective for sleep and anxiety. However, some have found that going up to doses of 400, 600, or even 800 mg was more helpful for anxiety. (A cup of green tea has about 25 mg of L-theanine.)

A good practice when starting any new supplement regimen is to start with the lowest dose that may be effective and to increase it if needed. This will minimize the possible negative side effects, both in the short-term and over time. Talk to your doctor to help you arrive at a dose that is best suited for your needs.

What to Look For

Widely available for purchase online, L-theanine supplements are sold in many natural-food stores and in stores specializing in dietary supplements.

Be sure to read the label as you assess which L-theanine product is right for you. There will be a Supplement Facts label on the packaging listing the active ingredients per serving as well as any added ingredients such as fillers, binders, and flavorings.

There also may be a seal of approval from a third-party quality testing organization such as ConsumerLab. While this seal does not guarantee safety, efficacy, or evaluation by the U.S. Food and Drug Administration (FDA), it is useful in establishing that the product contains the ingredients listed on the label, was manufactured properly, and does not contain a harmful amount of contamination.

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  1. White DJ, de Klerk S, Woods W, Gondalia S, Noonan C, Scholey AB. Anti-Stress, Behavioural and Magnetoencephalography Effects of an L-Theanine-Based Nutrient Drink: A Randomised, Double-Blind, Placebo-Controlled, Crossover TrialNutrients. 2016;8(1):53. doi:10.3390/nu8010053

  2. Unno K, Tanida N, Ishii N, et al. Anti-stress effect of theanine on students during pharmacy practice: positive correlation among salivary α-amylase activity, trait anxiety and subjective stressPharmacol Biochem Behav. 2013;111:128-135. doi:10.1016/j.pbb.2013.09.004

  3. Unno K, Noda S, Kawasaki Y, et al. Reduced Stress and Improved Sleep Quality Caused by Green Tea Are Associated with a Reduced Caffeine ContentNutrients. 2017;9(7):777. doi:10.3390/nu9070777

  4. Hidese S, Ota M, Wakabayashi C, et al. Effects of chronic l-theanine administration in patients with major depressive disorder: an open-label studyActa Neuropsychiatr. 2017;29(2):72-79. doi:10.1017/neu.2016.33