L-Theanine: Usage, Health Benefits & Side Effects

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Stress and anxiety are inevitable in life. Since we cannot divorce ourselves from stress, managing it or keeping our stress levels minimum is the next best thing.

L-theanine, a compound found in tea and some mushroom species, is believed to have a resounding relaxation effect. Apart from the dietary sources mentioned above, L-theanine is also available in supplement form.

L-theanine is believed to reduce stress and anxiety and also improve sleep. Aside from its calming effect, L-theanine comes with a host of other mental and physiological health benefits.

Keeping stress levels in check sounds divine because stress manifests in so many health issues. But does L-theanine work?

In this L-theanine overview, we look at its health benefits, safety factors, and dosing considerations. We also take a detailed look at how L-theanine works and the science behind its purported health benefits.

What is L-theanine?

L-theanine is an L-type, non-protein amino acid; L-type amino acids are only present in plants. L-theanine is present in the tea plant and select mushroom species (1).

L-theanine is a non-essential amino acid. The human body does not make it, and neither does it need it. However, much like phenolic compounds present in plants, it offers health benefits when taken.

L-theanine is present in beverages like green tea and black tea and can also be taken as an oral supplement.

L-theanine bears the same L-shape structure as that of glutamine (2). Glutamine is an essential amino acid that functions as a neurotransmitter (3).

Note, however, that there is limited data on the long-term effects of L-theanine supplementation.

Is L-theanine Safe?

L-theanine falls under the FDA’s (Food and Drug Agency) GRAS (Generally Recognized As Safe) category. It recommends up to 250mg per serving of L-theanine in food sources (6).

The FDA also approves the use of L-theanine as a dietary supplement.

A four-week study on L-theanine’s effects on stress-related symptoms also reported that L-theanine administration had no adverse effects (7).

Note, however, that there is limited data on the long-term effects of L-theanine supplementation.

L-theanine health benefits

Health Benefits of L-theanine

L-theanine has been linked to various mental health benefits.

It reduces stress by increasing the levels of chemicals such as serotonin in the brain (4). Serotonin is also referred to as the “happy chemical” because of its anti-depressant properties (5).

Other brain chemicals affected by L-theanine include dopamine, oxytocin, and endorphins.

The proponents of L-theanine have linked to a host of mental and physiological benefits. The benefits range from mundane ones like better sleep to notable benefits like aiding in the treatment of certain cancers.

The question remains, can L-theanine provide all the above benefits? We will look at L-theanine benefits alongside scientific evidence on the same.

In no particular order, below are some of the health benefits associated with L-theanine.

1. Anxiety and stress relief

L-theanine advocates vouch for its calming effect. They say that L-theanine works by reducing the level of chemicals that trigger anxiety in the brain.

It also increases the level of chemicals that promote relaxation.

What the Science Says

Multiple tests on brain activity after L-theanine ingestion prove that L-theanine directly impacts alpha frequency brain waves. The brain generates the alpha frequency when one is awake but relaxed, such as when watching a comedy show (8).

The test results were on an electroencephalogram (EEG), which is a test record of brain activity.

One study was to establish the effects of dietary L-theanine on healthy individuals. The participants were divided into two groups; one group was given an L-theanine solution and the other a placebo.

45 minutes after ingesting the respective solutions, there was a review of the participants’ EEG recordings. The checks continued every 15 minutes for the next hour.

The EEG results revealed an increase in alpha waves among the group that took L-theanine. It also showed that the alpha waves increased with time (9).

That means that L-theanine increases brain relaxation without inducing drowsiness.

2. Improved symptoms of mental conditions including depression, schizophrenia, and ADHD

There is also a belief that L-theanine can reduce symptoms among persons with mental illnesses like schizophrenia, ADHD, and depression.

Its proponents say that it can be used as an adjunctive or additional medication for treating these illnesses.

What the Science Says

A review study was conducted on data related to L-theanine administration’s effects on stress and anxiety disorders.

The review concluded that the administration of 200-400mg of L-theanine daily for eight weeks induced an anxiolytic effect. An anxiolytic or antianxiety agent is a medication or any other form of intervention that treats anxiety symptoms (10).

The review was conducted among sample groups of participants with acute and chronic mental health illnesses (11).

There were separate studies on the efficacy of L-theanine in reducing symptoms for the above illnesses. Each illness had an independent study.

It emerged that L-theanine can counter depressive symptoms, anxiety, and sleep disturbances among patients diagnosed with clinical depression (12). It also countered anxiety among subjects with schizophrenia (13).

However, note that L-theanine only supplements but cannot replace the prescribed medication for the mental illnesses above. The research studies above also recommended further research be conducted on L-theanine.

They recommend the use of larger populations to establish L-theanine’s clinical significance and long-term effects on patients.

3. Improved cognitive function and memory

L-theanine supplements are also popular among students for improving concentration and memory.

What the Science Says

Multiple studies back the notion that L-theanine improves cognitive abilities like attention, memory, information processing, and multi-tasking.

There was one study among two groups of subjects with mild cognitive disorder. One group took a dose of L-theanine and the other a placebo.

The EEG readings of the subjects were taken three hours afterward. The readings showed an increase in beta brain waves in the subjects who took L-theanine (14).

Beta brain waves are produced when one is fully awake, and the brain is actively working.

In another study, two groups of university students, one group with a high propensity for anxiety, were dosed with L-theanine. The results revealed high attention performance and reaction time among the group with a high propensity for anxiety.

However, the L-theanine made no difference among students with a low propensity for anxiety (15).

Other studies have also shown that a combination of L-theanine and caffeine work best together. The combination improves more cognitive functions within a shorter period than each substance taken on its own (16).

4. Better sleep quality and patterns

L-theanine has also been credited with improving sleep quality.

What the Science Says

Several tests conducted in humans and animals reveal that L-theanine improves various aspects of sleep. In a randomized placebo-controlled study, the participants were given either 200mg of L-theanine or a placebo over a four-week duration.

The participants’ Pittsburgh Sleep Quality Index (PSQI) was taken before the test. PSQI is a self-rating questionnaire used to assess sleep quality (17).

After the four-week duration, the participants who had taken L-theanine showed improved scores on their second PSQI test (18).

Another study was undertaken to investigate the effects of a combination of L-theanine and Gamma-aminobutyric acid (GABA) on sleep. GABA is an inhibitory neurotransmitter that hinders the chemicals that send messages to neurons (brain nerve cells).

GABA inhibits the neurons from triggering action in the brain, causing relaxation and even sleep (19).

The EEG of participants was taken to establish total sleeping time and quality of sleep. The results showed a significant improvement in sleep latency (the duration it takes to transition from wakefulness to sleep).

It also showed significant improvement in both REM and non-REM sleep (20).

5. Blood pressure control

What the Science Says

A study was conducted to establish L-theanine’s effects on both the mind and physiological conditions under stressful circumstances.

The selected participants were more excitable to stressful stimuli. In the placebo-controlled study, participants were either given an L-theanine dose or a placebo.

The results revealed that L-theanine prevented a blood-pressure spike in people with a high propensity to stress under strenuous situations (21).

Note, however, that there are no studies on L-theanine regulation of blood pressure under normal circumstances. There are also no studies on its blood pressure effect on people with risk factors of cardiovascular disease.

6. Improved immunity

L-theanine is believed to enhance body immunity.

What the Science Says

Several studies associate L-theanine with improved immune response. According to these studies, it does so by maintaining a state of balance between immune cells called cytokines.

According to a study conducted using rats, 400mg of L-theanine improved rats’ immune functions (22). Another study conducted among elite athletes after strenuous training showed that L-theanine also inhibited the production of interleukin 10 (IL-10).

IL-10 inhibits the production of anti-inflammatory cytokines, which regulate immunity response (23).

7. Tumor and cancer treatment

L-theanine is also believed to aid in tumor suppression and the treatment of some types of cancer.

What the Science Says

A study was conducted to determine the effects of L-theanine on human lung and leukemia cancer cells. The study also aimed to establish the effects of L-theanine on the migration of cancerous cells.

Results from the study showed that L-theanine demonstrated anti-cancer activity against leukemia and lung cancer cells. It suppressed the growth of the cancerous cells (24).

Other studies also showed that L-theanine’s anti-cancer activity stemmed from its ability to enhance anti-cancer agents’ functions. The anti-cancer agents reduce the viability of cancer cells (25).

L-theanine Side Effects

As previously stated, L-theanine is generally safe. However, some people have exhibited the following mild symptoms while taking L-theanine.

  • Headache
  • Nausea
  • Irritability

The symptoms above can occur from taking L-theanine in green tea and also while taking the supplement form. If the symptoms persist, you should stop taking L-theanine and see a doctor.

L-theanine Usage and Dosing Consideration

Most studies on L-theanine use L-theanine doses of between 200mg to 800mg per day. Continuous use of L-theanine in these doses showed neither adverse effects nor toxicity.

The FDA has no directive on the safe daily recommended dose of L-theanine. However, most L-theanine supplement manufacturers stick to 200mg per tablet.

Note that there is no data on the long-term effects of L-theanine. Therefore, even with the vast grey area on dosing, you may want to tread lightly. Do not take more than the recommended prescription to either speed up results or sustain performance for longer.

L-theanine Sources

Risks and Precautions

Although L-theanine is considered generally safe, there are specific categories of people for whom it is not considered safe.

There isn’t enough reliable data on L-theanine’s effects on pregnant and lactating mothers, for starters. To be safe, just avoid taking it altogether while pregnant or nursing.

There is also the issue of medical interactions. L-theanine may inhibit the effectiveness of some medications. If you are on medication, consult your doctor before you start taking L-theanine.


How long does it take L-theanine to kick in when taken for anxiety or focus?

An L-theanine dose of between 50mg to 200mg takes 30 to 40 minutes for the calming effect to kick in. The effect should last between eight to 10 hours.

Can I take L-theanine with other supplements?

L-theanine has been proven to work well in collaboration with other supplements like magnesium, vitamin B, and caffeine. Note, however, that the issue of interaction still stands.

If you would like to take L-theanine alongside other supplements, please consult your doctor first.

Does L-theanine make you happy?

L-theanine has a calming effect when one is anxious because it heightens the production of alpha waves. The research on its effect on “feel good” hormones like serotonin, dopamine, and oxytocin remains inconclusive.

Is it safe to take L-theanine daily?

While L-theanine is considered generally safe, there is no data on the effects of long-term use.


From the above information, it seems that L-theanine is quite effective in the mental benefits it offers. It has a notable positive effect on anxiety, stress, and sleep.

It also has great potential as an anti-cancer agent. Better still, it is considered safe to take and has minimal side effects.

Note, however, that all the L-theanine studies we have cited above recommended that further research. In most cases, its clinical viability is not yet established.

All in all, L-theanine has more pros than cons. If you decide to take it as a supplement, ensure you consult your doctor first and stick to the prescribed dose.


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