Jun. 09, 2025
L-theanine is an amino acid that is found primarily in dietary sources like green tea and matcha. Most often studied for its effects on reducing stress and promoting calmness, L-theanine also supports sleep, immune function, and blood pressure control.
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In this article, we will discuss what L-theanine is, where it’s found, and the top five health-promoting benefits that it has.
L-theanine is a unique amino acid commonly found in green tea leaves but is also in smaller amounts in black tea, white tea, and some mushrooms.
It’s unique in that it doesn’t function as a building block to proteins, as most other amino acids do. It’s not commonly found in foods and is not required by our bodies. Therefore, L-theanine is considered a non-dietary, nonessential amino acid.
Even though it is deemed nonessential, there are several health-promoting properties associated with L-theanine. The primary benefit of L-theanine is that it stimulates a calm and focused state of mind, relieves stress and promotes calmness, and leads to better sleep.
The calming effects of L-theanine stem from its ability to produce the neurotransmitters GABA and dopamine, which have relaxation-promoting qualities. At the same time, L-theanine also reduces levels of glutamate, an excitatory neurotransmitter. It does this by binding to glutamate receptors and increasing GABA, which competes with glutamate’s re-uptake in the brain.
Structurally, L-theanine is very similar to the amino acid glutamine, which produces glutamate. Through L-theanine, the upregulation of GABA can counterbalance glutamate levels.
Although some glutamate is still needed for a healthy brain, excess amounts can increase stress and agitation. GABA and glutamate have sometimes been referred to as the yin and yang of neurotransmitters, as the combination of the sedative-like properties of GABA and the excitatory nature of glutamate creates a perfect amount of stimulation when in balance.
This yin-yang balance makes L-theanine a natural anxiolytic, a medication or therapeutic intervention that reduces symptoms of unease or agitation. However, unlike prescription anxiolytics, L-theanine can bring on the calm without creating drowsiness.
Research has also backed up the anxiolytic properties of L-theanine. An October study published in Nutrients randomized 30 adults to receive either 200 mg per day of supplemental L-theanine or a placebo. Those in the L-theanine group had significantly reduced levels of low mood, stress, and agitation after four weeks.
Another study published in Nutrients found that adults who consumed a beverage containing 200 mg of L-theanine had reductions in their response to a cognitive stress test one hour after drinking it and reductions in salivary cortisol levels three hours later.
In the October study in Nutrients, adults who took 200 mg of L-theanine before bed also had significant reductions in sleep latency (the time it takes to fall asleep), sleep disturbances, and usage of sleeping medication throughout the four-week study.
The mechanisms behind how L-theanine benefits sleep are similar to that of its calming properties. Through GABA upregulation, L-theanine promotes a relaxing and calm state to wind down for bed.
Another related benefit of L-theanine is how it promotes a state of wakeful relaxation — the kind of peaceful brain state that you experience during meditation, creative work, or anything that puts you in a flow state.
L-theanine produces focused energy through its enhancement of alpha brain waves, which are associated with calmness, relaxation, and contentment, but without drowsiness or fatigue. Consumption of L-theanine in combination with caffeine — like green tea and matcha — amplifies the effects on cognition and focus. In a December trial published in Nutritional Neuroscience, a combination of 97 mg of L-theanine with 40 mg of caffeine led to significant improvements in accuracy during task switching and self-reported alertness and tiredness.
Lastly, L-theanine benefits cognition through its ability to increase brain-derived neurotrophic factor (BDNF), a protein that is essential for maintaining and growing new neurons. BDNF is known to be neuroprotective.
L-theanine has been shown to modulate blood pressure through two mechanisms. First, stress can elevate blood pressure by increasing levels of vasoconstricting hormones, and L-theanine is known to reduce stress.
Secondly, L-theanine can stimulate nitric oxide production, which is a vasodilator that reduces blood pressure.
A study published in the Journal of Physiological Anthropology found that 200 mg of supplemental L-theanine was able to attenuate blood pressure elevation that was induced by stressful mental tasks. The greatest improvement was seen in people considered “high responders” because they typically have elevated blood pressure in stressful situations.
While these results are promising for acute blood pressure control, no studies have been done assessing L-theanine’s effects on longer-term blood pressure regulation.
Lastly, L-theanine may support immune system functioning through its ability to upregulate certain immune cells and decrease pro-inflammatory compounds. L-theanine has been shown to enhance the innate immune system, our body’s first line of defense against pathogens, through regulation of cytokines.
A common combination used in studies on immune function is L-theanine with L-cysteine, another amino acid. Research has shown that this combination is linked to improved immune function in endurance athletes as well and the elderly population.
Although more research still needs to be done on the effects of L-theanine on immunity, the results so far are encouraging.
Although you can get L-theanine from green tea and matcha, more benefits are seen with higher amounts found in supplements. Matcha, a powder made up of green tea leaves, has higher L-theanine than green tea, which is just the water that the tea leaves were steeped in.
One cup of tea contains approximately 25 mg of L-theanine, whereas supplements range from 50 to 200 mg. In the studies mentioned in this article, 200 mg of L-theanine per day was the most common dosage.
Whether you’re drinking tea or taking a supplement, L-theanine has been shown to cross over the blood-brain barrier and take effect within 30 to 120 minutes of ingesting it.
There are no major side effects reported with L-theanine usage. However, people taking blood pressure medications may want to be careful due to the potential blood pressure-lowering effects of L-theanine.
If you are pregnant, breastfeeding, or tend to have low blood pressure, ask your doctor before consuming L-theanine in supplemental form.
References:
Giesbrecht T, Rycroft JA, Rowson MJ, De Bruin EA. The combination of L-theanine and caffeine improves cognitive performance and increases subjective alertness. Nutr Neurosci. ;13(6):283‐290. doi:10./X
Suggested reading:Contact us to discuss your requirements of L-Theanine for Cognitive. Our experienced sales team can help you identify the options that best suit your needs.
Hidese S, Ogawa S, Ota M, et al. Effects of L-Theanine Administration on Stress-Related Symptoms and Cognitive Functions in Healthy Adults: A Randomized Controlled Trial. Nutrients. ;11(10):. Published Oct 3. doi:10./nu
Juszkiewicz A, Glapa A, Basta P, et al. The effect of L-theanine supplementation on the immune system of athletes exposed to strenuous physical exercise. J Int Soc Sports Nutr. ;16(1):7. Published Feb 15. doi:10./s-019--y
Li C, Tong H, Yan Q, et al. L-Theanine Improves Immunity by Altering TH2/TH1 Cytokine Balance, Brain Neurotransmitters, and Expression of Phospholipase C in Rat Hearts. Med Sci Monit. ;22:662‐669. Published Feb 28. doi:10./msm.
Lorenz M, Urban J, Engelhardt U, Baumann G, Stangl K, Stangl V. Green and black tea are equally potent stimuli of NO production and vasodilation: new insights into tea ingredients involved. Basic Res Cardiol. ;104(1):100‐110. doi:10./s-008--3
Lyon MR, Kapoor MP, Juneja LR. The effects of L-theanine (Suntheanine®) on objective sleep quality in boys: a randomized, double-blind, placebo-controlled clinical trial. Altern Med Rev. ;16(4):348‐354.
Nobre AC, Rao A, Owen GN. L-theanine, a natural constituent in tea, and its effect on mental state. Asia Pac J Clin Nutr. ;17 Suppl 1:167‐168.
Ota M, Wakabayashi C, Sato N, et al. Effect of L-theanine on glutamatergic function in patients. Acta Neuropsychiatr. ;27(5):291‐296. doi:10./neu..22
Rothenberg DO, Zhang L. Mechanisms of Regular Tea Consumption. Nutrients. ;11(6):. Published Jun 17. doi:10./nu
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 Trial. Nutrients. ;8(1):53. Published Jan 19. doi:10./nu
Williams J, Kellett J, Roach P, et al. l-Theanine as a Functional Food Additive: Its Role in Disease Prevention and Health Promotion. Beverages. ;2(2):13. doi:10./beverages
If you haven’t heard of L-Theanine, then you might be surprised to know that this amino acid has some pretty beneficial actions on the body. Found in green tea, L-Theanine is an amino acid that can help improve cognitive performance, calm the mind and enhance mental alertness.
But what exactly is it and what does it do? In this article, we’ll take you through the role of L-Theanine and how you can get more of it into your diet.
L-Theanine is the most common form of Theanine, a naturally occurring amino acid that can help mind relaxation1.
First discovered by Japanese scientists in , L-Theanine is found in green tea. It’s actually one of the components that gives green tea its distinct taste2. You can also find it in black tea and certain types of mushrooms.
L-Theanine and L-Tyrosine are two amino acids known for their ability to aid in relaxation. L-Theanine is naturally found in tea leaves and is known for its effects on calming the mind.
On the other hand, L-Tyrosine is an amino acid produced by the body from another amino acid called phenylalanine. It’s also found in a number of high-protein foods, including chicken, beef, fish, dairy, eggs and nuts3. Like L-Theanine, L-Tyrosine is known to help improve concentration, clarity and focus4.
With all that covered, you might be wondering what are the benefits? L-Theanine supports mind relaxation by contributing to several key changes in the brain5, 6, 7.
Let’s take a closer look.
L-Theanine has a unique function on the brain, contributing to various aspects of mental function well-being. L-Theanine influences certain chemicals in the brain that influence mind relaxation and overall cognitive function.
L-Theanine impacts GABA, short for Gamma-Aminobutyric Acid, an inhibitory neurotransmitter that helps reduce nerve cell activity. By increasing levels of GABA in the brain, it signals to your body that it’s time to relax, which can help alleviate feelings of stress and help you enjoy a more restful, longer sleep8. At the same time, L-Theanine boosts dopamine and serotonin levels, enhancing mood, emotional stability, motivation and cognitive function9.
To dive a little deeper, L-Theanine enhances the production of alpha brain waves, which are associated with a state of relaxed alertness10. This brain wave pattern is typically observed during meditation11 and has been linked to increased creativity and focus while maintaining a state of calmness and relaxation.
This combination of increased alpha brain activity and neurotransmitter levels helps with cognitive function12.
Thanks to its impact on mental function and cognitive performance, L-Theanine is considered a nootropic. Nootropics are substances that can enhance cognitive function in healthy individuals. L-Theanine is typically used for its cognitive-enhancing properties, including increased relaxation and improved cognitive function13, 14.
You can boost your daily intake of L-Theanine through diet and supplementation. As one of the richest natural sources of L-Theanine, drinking green tea can help boost your daily intake. Alternatively, you may like to consider taking an L-Theanine supplement.
L-Theanine is generally considered okay to take daily to help with mind relaxation and cognitive performance15, 16.
The best time to take L-Theanine often depends on the effects you’re trying to benefit from. If you’re hoping to enhance mental alertness and cognitive function, it’s often recommended to take an L-Theanine supplement when you need the extra boost to help you power through the situation. However, if you’re looking to calm the mind, it may help to take an L-Theanine supplement in the evening.
But remember, be sure to consult with your healthcare professional before making changes to your diet, nutritional intake or introducing a new supplement to your daily routine.
Want to learn more about supplements and brain health? Check out the Swisse Wellness Hub for more information on mindfulness, nutrition and more.
Resources:
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