The Scientific Evidence Behind L-Theanine’s Health Benefits

Written by Andy Mobbs
featured image for article on seneca ingredient l-theanine

In this article, you’ll learn all about the amazing health benefits of L-theanine, specifically how it can reduce stress and anxiety, as well as boost brain health and cognitive function.

What is L-Theanine?

L-theanine is an amino acid that’s found naturally in all teas and some plant extracts but is most abundant in green tea. It’s actually thought that the thiamine content in green tea is the main reason why people feel relaxed after drinking it. It’s also used as a supplement to help people cope with stress and reduce their anxiety (1).

This reduction in stress allows people taking theanine to reduce their inflammation, sleep better, and think more clearly.

How does L-theanine work?

One of the main ways that thiamine works is by being able to control levels of a neurotransmitter called glutamate. Glutamate’s main role is as an excitatory neurotransmitter. This means it has a ‘switching on’ effect in the brain and is key for normal brain functioning as well as focus, learning, and memory.

Reduced Glutamate Toxicity

However, in today’s world where most of us have access to more than enough calories, we normally also have more than enough glutamate. This, together with chronic stress and inflammation, can also cause too much activation of the receptors in the brain by glutamate.

This excess activation can become toxic to brain cells, aka neurons, which can lead to damage or even death of the cells. This can potentially cause many problems from poor sleep and feeling too wired and stressed, to diseases like depression and dementia.

Theanine is able to reduce excess levels of glutamate, by actively binding at the site on neurons that glutamate binds to in a process called ‘competitive inhibition. This means theanine is able to inhibit glutamate’s ability to activate neurons and become toxic (2, 3).

competitive inhibition

Theanine is also able to reduce the uptake of glutamine into the neurons, which is then turned into glutamate and is a second way that theanine can moderate excess glutamate levels (4).

Increased GABA and Glycine

Theanine doesn’t just help reduce excess levels of glutamate in the brain though, it actually helps to increase levels of the neurotransmitters GABA and glycine. GABA and glycine are both inhibitory neurotransmitters and have an opposite effect to glutamates’ excitatory effects. GABA, for example, can promote feelings of calm and relaxation, and GABA receptors are the ones that tranquilizer drugs like benzodiazepines such as valium work on (5, 6).

By increasing levels of GABA and glycine, theanine can help to calm down the brain and CNS and work against anxiety.

Increased levels of BDNF

Theanine has also been shown to increase levels of BDNF (brain-derived neurotrophic factor). BDNF is a growth hormone for the brain and helps the growth and repair of neurons as well as synaptic plasticity, or the ability to be able to form new connections to learn things (7).

Serotonin and Dopamine

It’s also been shown that theanine is able to increase levels of the neurotransmitters Serotonin and Dopamine in the brain (8). These neurotransmitters are associated with motivation, focus, learning, and feeling good. In fact, low levels of them have all been associated with anxiety and depression.

Increased Alpha Brain Waves

Studies have also shown theanine can increase levels of alpha brainwaves (9, 10). Alpha brainwaves are associated with relaxed focus, better concentration, and improved overall cognitive function.

Show me the Science!

Reduced Stress

A Japanese study gave 12 subjects a mental arithmetic test designed to challenge the participants and create stress. They conducted the test 4 times, with either 200mg of Theanine at the start or halfway through, and then compared these results to controls with no supplementation and one with a placebo. At the end of the test, they found that heart rate and salivary immunoglobulin A levels were lower in the tests where the subjects were supplemented with theanine (11). Immunoglobulin A is an antibody and the production of it is increased by the immune system during stress.

A further study tested 34 subjects on a further cognitive stress test and found that participants who had supplemented with 200mg theanine had lower salivary cortisol levels (12).

Reduced Anxiety

40 patients with schizophrenia were given 400mg of theanine per day in addition to their normal medication and then compared to another 20 patients who were given a placebo. At the end of the 8 week period, the patients who had received theanine had lower anxiety, lower cortisol measures, lower dysphoric mood measures (i.e feelings of anger, depression, irritability), and increased levels of BDNF (13).


20 patients suffering from major depressive disorder were given 250mg of theanine per day for 8 weeks, in addition to their current medication. At the end of the 8 week period, the researchers found that the patients scored lower on markers of depression, had lower anxiety, better quality sleep, and had improved cognitive function and memory scores (14).

Reduced Blood Pressure

Caffeine can increase blood pressure. However, when theanine is taken with caffeine, one study on 48 adults who received 250mg of caffeine and 200mg of theanine, found that theanine was able to prevent the caffeine-induced increase in blood pressure (15).

A further study showed that theanine could prevent the increase in blood pressure that happened during cognitive tests designed to invoke a stressful response (16).

L-Theanine helps improve memory

91 subjects with mild cognitive impairment, which is considered the first stage when symptoms of dementia become apparent, were enrolled in a randomized double-blind study. Half took 1680mg of theanine per day for 16 weeks.

At the end of the study period, the subjects who had taken the theanine scored better on memory tests than those who had taken the placebo. The researchers also found that the theanine group showed signs of theta brain waves which are related to a high level of cognitive awareness and something that advanced meditators strive to achieve (17).

Alzheimer’s disease

In addition to mild cognitive impairment, there has been a further study looking at a mouse model of Alzheimer’s and the effects of theanine supplementation on it.

In the study, researchers injected amyloid beta proteins into the brains of mice. Amyloid-beta proteins form the basis of amyloid plaques which are found in the brains of Alzheimer’s patients. The process of injecting the amyloid-beta proteins creates neuronal cell death and causes memory impairment, effectively giving the mice Alzheimer’s. The researchers then added theanine to the drinking water of half the mice for 5 weeks.

They found that the group that was given theanine performed better on memory tests than the group that wasn’t. Also, after dissecting the brains of the mice, they found less neuronal cell death and oxidative damage to the proteins and lipids in the brains of the mice who had been given theanine. They also found higher levels of the body’s main antioxidant glutathione in the supplemented mice, indicating an upregulation of antioxidant production.

Obviously, these types of studies can’t be performed on humans as you can’t inject amyloid-beta proteins into human brains. However, it does provide exciting results that will hopefully pave the wave for more studies on theanine supplementation in Alzheimer’s patients (18).

Improved Sleep

A placebo-controlled trial on 98 8-12-year-old boys that had been diagnosed with ADHD looked at whether theanine could help improve their sleep (this is often affected in ADHD). Half the participants were given 100mg of theanine per day for 6 weeks. At the end of the 6 week period, the researchers found high sleep percentages and sleep efficiency scores in the group that supplemented with theanine (19).

A further study gave 17 patients with schizophrenia 250mg of theanine per day for 8 weeks in addition to their normal antipsychotic medication. Researchers also found an improved quality of sleep in the patients (20).

Final thoughts

To sum up this article, L-theanine’s benefits go beyond reducing stress and anxiety. It can also help improve focus, learning, and memory, amongst many other benefits. With that being said, it is because of L-theanine’s brain benefits that we’ve added it to our Seneca Nootropic Complex.

Seneca is a non-stimulating nootropic and cognitive enhancing supplement. Each serving contains 200mg of L-theanine HCL, along with 17 other natural nootropics formulated to boost mental health and restful sleep. Check out this article (What are nootropics) if you want to know more about these brain support supplements!


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