5 Potential Health Benefits of Theanine

Health Benefits, Uses, Side Effects, & More

Green tea pour and assorted loose teas
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Theanine (sometimes referred to as "L-theanine") is an amino acid that is naturally found in green tea. It is also available in supplement form and it is said to offer a number of health benefits. Before taking theanine (or any supplement), however, it's important to learn more about it and understand any safety concerns.

Uses for Theanine

Proponents claim that theanine can help with a variety of health concerns.

These include anxiety, depression, high blood pressure, high cholesterol, insomnia, and stress.

Theanine is also purported to increase concentration, promote weight loss, and boost the immune system. In addition, some proponents suggest that theanine can prevent strokeAlzheimer's disease, and some forms of cancer.

5 Potential Health Benefits of Theanine

To date, few clinical trials have tested the health effects of theanine. However, preliminary research indicates that theanine may offer certain health benefits. 

1) Reduce Stress

Theanine may help reduce the negative effects of stress, according to a small study published in Biological Psychology in 2007. In an experiment involving 12 people, researchers found that theanine-treated participants were less likely to experience an increased heart rate when performing a stressful task.

A 2016 study attempted to isolate the stress-relieving benefits of theanine from the caffeine found in green tea.

Tests were conducted on mice who were given three teas with various levels of caffeine and theanine.

The results showed that the green tea with enhanced theanine and lower caffeine was most effective at reducing stress. Researchers believe that the theanine counteracted the effects of caffeine, which can increase stress.

2) Boost Immunity

Taking green-tea-derived theanine and antioxidants in supplement form may help prevent the flu. That is a suggestion from a study published in BMC Complementary and Alternative Medicine in 2011.

Every day for five months, the study's 197 participants took either a placebo or a capsule containing theanine and catechins (a class of antioxidants found in green tea). Results revealed that the incidence of flu was significantly lower in the theanine/catechin group compared to the placebo group.

3) Improve Brain Health

A 2010 study from Nutritional Neuroscience suggests that a combination of theanine and caffeine may help improve cognitive performance.

For the study, 44 young adults took either a placebo or a combination of theanine and caffeine prior to performing a demanding cognitive task. Researchers found that the combination of theanine and caffeine significantly improved accuracy and alertness. It also helped to increase focus while performing the task.

Additionally, findings from an animal-based study published in Free Radical Biology & Medicine in 2009 suggests that theanine may inhibit the buildup of amyloid beta. This is a substance that forms the brain plaques associated with Alzheimer's disease.

4) Relieve Depression

Theanine may help relieve depression, according to an animal-based study published in Phytotherapy Research in 2011. In tests on mice, scientists discovered that theanine produced an "antidepressant-like effect."

In people with major depressive disorder, a 2017 study published in Acta Neuropsychiatrica showed similar results. The trial included 20 men and women who had 250 mg of L-theanine added to their current medications for eight weeks. They found that it had multiple benefits in relieving anxiety, sleep disturbances, and cognitive impairments associated with depression.

5) Help for Weight Loss

Theanine shows promise as a weight loss aid, according to animal-based research published in the journal In Vivo in 2004. In an experiment involving mice fed green tea powder, researchers found that theanine and caffeine found in the powder appeared to prevent weight gain and fight the buildup of fat.

Safety Concerns of Theanine

To date, little is known about the safety of taking theanine supplements in the long term. Theanine is generally considered safe when consumed in green tea. However, the National Institutes of Health 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 theanine in combination with sedatives, lipid-lowering medications, and/or drugs used in chemotherapy may produce harmful effects.

Where to Find Theanine Supplements

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

Using Theanine for Health

While increasing your theanine intake by consuming green tea on a regular basis may help enhance your overall health, it's too soon to recommend theanine supplements for any health condition. 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.

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

If you're considering the use of theanine supplements, talk with your doctor first. Self-treating a condition and avoiding or delaying standard care may have serious consequences.


Giesbrecht T, Rycroft JA, Rowson MJ, De Bruin EA. The Combination of L-Theanine and Caffeine Improves Cognitive Performance and Increases Subjective Alertness. Nutritional Neuroscience. 2010 Dec;13(6):283-90. doi: 10.1179/147683010X12611460764840.

Hidese S, et al. Effects of Chronic L-Theanine Administration in Patients With Major Depressive Disorder: An Open-Label Study. Acta Neuropsychiatrica. 2017 Apr;29(2):72-79. doi: 10.1017/neu.2016.33.

Kim TI, Lee YK, Park SG, Choi IS, Ban JO, Park HK, Nam SY, Yun YW, Han SB, Oh KW, Hong JT. L-Theanine, an Amino Acid in Green Tea, Attenuates Beta-Amyloid-Induced Cognitive Dysfunction and Neurotoxicity: Reduction in Oxidative Damage and Inactivation of Erk/p38 Kinase and Nf-Kappab Pathways. Free Radical Biology & Medicine. 2009 Dec 1;47(11):1601-10. doi: 10.1016/j.freeradbiomed.2009.09.008.

Kimura K, Ozeki M, Juneja LR, Ohira H. L-Theanine Reduces Psychological and Physiological Stress Responses. Biological Psychology. 2007 Jan;74(1):39-45.

Matsumoto K, Yamada H, Takuma N, Niino H, Sagesaka YM. Effects of Green Tea Catechins and Theanine on Preventing Influenza Infection Among Healthcare Workers: a Randomized Controlled Trial. BMC Complementary and Alternative Medicine. 2011 Feb 21;11:15. doi: 10.1186/1472-6882-11-15.

Turkozu D, Sanlier N. L-Theanine, Unique Amino Acid of Tea, and Its Metabolism, Health Effects, and Safety. Critical Reviews in Food Science and Nutrition. 2017 May 24;57(8):1681-1687. doi: 10.1080/10408398.2015.1016141.

Unno K, et al. Anti-Stress Effects of Drinking Green Tea With Lowered Caffeine and Enriched Theanine, Epigallocatechin and Arginine on Psychosocial Stress Induced Adrenal Hypertrophy in Mice. Phytomedicine. 2016 Nov 15;23(12):1365-1374. doi: 10.1016/j.phymed.2016.07.006.

Yin C, Gou L, Liu Y, Yin X, Zhang L, Jia G, Zhuang X. Antidepressant-Like Effects of L-Theanine in the Forced Swim and Tail Suspension Tests in Mice. Phytotherapy Research. 2011 Nov;25(11):1636-9. doi: 10.1002/ptr.3456.

Zheng G, Sayama K, Okubo T, Juneja LR, Oguni I. Anti-Obesity Effects of Three Major Components of Green Tea, Catechins, Caffeine and Theanine, in Mice. In Vivo. 2004 Jan-Feb;18(1):55-62.

Disclaimer: The information contained on this site is intended for educational purposes only and is not a substitute for advice, diagnosis or treatment by a licensed physician. It is not meant to cover all possible precautions, drug interactions, circumstances or adverse effects. You should seek prompt medical care for any health issues and consult your doctor before using alternative medicine or making a change to your regimen.