L-Theanine: Everything You Need To Know (2024)

L-theanine is an amino acid found in tea leaves (Camellia sinensis) and the Bay bolete mushroom (Xerocomus badius). L-theanine is also available in supplement form.

Clinical trials suggest L-theanine has antianxiety effects and promotes relaxation, sleep, cognitive function (processing and understanding information), and more.

Different types of tea have different amounts of L-theanine. One study suggested white and green teas contain more L-theanine than oolong and black. Prepared teas were found to have anywhere from 5 to 36 milligrams (mg) of L-theanine per cup.

The longer tea leaves are steeped, the more L-theanine (and caffeine) is extracted. Maximum levels can take up to 20 minutes or more to develop.

Read on for more about L-theanine's benefits, safety, and more.

Supplement Facts

  • Active ingredient(s): 5-N-ethyl-L-glutamine
  • Alternate name(s): 5-N-ethyl-L-glutamine, γ-glutamylethylamide, Suntheanine, theanine
  • Legal status: Over-the-counter supplement. Generally recognized as safe (GRAS).
  • Suggested dose: Varies by condition.
  • Safety considerations: Pregnancy, breastfeeding, chemotherapy; potential interactions with medications and other supplements, such as those for blood pressure.

What Are L-Theanine’s Benefits?

Supplement use should be individualized and vetted by a healthcare professional, such as a registered dietitian nutritionist (RD or RDN), pharmacist, or healthcare provider. No supplement is intended to treat, cure, or prevent disease.

Researchers have studied L-theanine's effects for several conditions.

However, it's important to note that better-designed clinical trials are still needed.

L-Theanine: Everything You Need To Know (1)

ADHD Symptoms

Researchers have investigated L-theanine for attention deficit hyperactivity disorder (ADHD) symptoms.

Attention issues can have the following causes and/or associations:

  • Anxiety
  • Lead exposure
  • Brain injury
  • Family stress
  • Thyroid conditions
  • Inflammatory bowel conditions
  • Nutrition issues, including zinc or iron deficiency

Addressing any underlying issues is worth considering. If you have questions about your child's symptoms, it's best to contact their pediatrician.

A study was conducted in male children (8 to 15 years) with ADHD. L-theanine improved total cognition compared to a placebo (an inactive substance). Both L-theanine alone and an L-theanine-caffeine combination also reduced mind wandering.

Caffeine Use in Children

The American Academy of Child and Adolescent Psychiatry (AACAP) advises against caffeine for children under 12 years.

Some children with ADHD may also have significant issues with sleep. Sleep disturbances can impact both a child's and family's well-being.

A clinical study suggested L-theanine helped sleep quality in male children 8 to 12 years with ADHD.

Further, higher-quality studies are needed to confirm these results.

Correct Diagnosis of ADHD

Correctly diagnosing ADHD is essential. Some gifted (highly or profoundly intelligent) children may have behaviors that seem like ADHD due to boredom or other issues.

ADHD, autism spectrum disorder (ASD), and giftedness can also share overlapping characteristics and can be correlated. A healthcare provider well-versed in both giftedness and neurodiversity can help. Organizations like the National Association for Gifted Children have additional resources.

Another study showed younger males in kindergarten were, as a group, over-diagnosed with ADHD. Developmentally normal behavior has been mistaken for a medical issue. It may be that a lower student-to-teacher ratio (smaller class size) with experienced teachers may benefit children in this case as well.

Ask your child's healthcare provider about questions or concerns. They may refer you to a healthcare provider that specializes in these areas.


Anxiety affects around 12.5% of adults and 9.4% of children in the United States. Unresolved anxiety can cause further health issues.

Scientists found L-theanine has anxiolytic (anti-anxiety) effects. A systematic review (a collection of research on a single topic) suggested L-theanine reduced anxiety in people under stress.

Researchers conducted a study in children between 4 and 17 years with Tourette’s syndrome (a nervous system condition causing sudden twitches, movements, and sounds). L-theanine with vitamin B6 reduced tics with anxiety. It’s challenging to fully understand L-theanine's effects in this study alone as it was used in combination.

While there's promising evidence, conflicting evidence of theanine’s effectiveness for anxiety also exists.

Speak with your healthcare provider if you're experiencing anxiety.


Scientists have suggested caffeine may bolster L-theanine’s impact on cognition (processing and understanding information) and working memory.

In a study of young adults, L-theanine with caffeine helped with attention.

However, in other studies of healthy adults, L-theanine alone (no caffeine added) had the following effects:

  • Decreased errors
  • Increased attention
  • Enhanced working memory
  • Promoted verbal fluency (retrieving information from memory)
  • Improved executive function
  • Increased selective attention (the ability to select and process information while tuning out distractions)


Theanine has been investigated for its anticancer effects in in vitro (in cells in a laboratory) and in vivo (animal) studies.

However, clinical trials (research in humans) are needed before recommendations can be made.


In one study, researchers added L-theanine to current medication in people with major depressive disorder. The following symptoms improved:

  • Depressive symptoms
  • Anxiety
  • Sleep disturbance
  • Cognitive impairments

Further, high-quality studies are needed.

Please reach out to your healthcare provider if you're experiencing depression. Promptly diagnosing and treating this and other mental health issues is important.

Immune Effects

L-theanine impacts the immune system. In a study of professional athletes, L-theanine affected different immune system markers. It was associated with decreased interleukin-10 (IL-10).

Further study is needed.


In people with schizophrenia or schizoaffective disorder, L-theanine was added to regular treatment with beneficial effects.

L-theanine supplementation was associated with the following improvements:

  • Sleep quality
  • Positive and Negative Syndrome Scale (PANSS) scores (assesses how well treatment is working)

Consult with your healthcare provider before adding supplements to your medication regimen.


Chronic sleep disorders can seriously affect your quality of life. Sleep disorders are linked with or can worsen the following conditions:

  • Anxiety
  • Cardiovascular disease
  • Depression
  • Diabetes

In healthy adults, L-theanine reduced sleep latency (the time it takes to fall asleep), sleep disturbance, and the use of sleep medication.

Some children with ADHD have associated sleep problems, affecting both the child's and family’s well-being. In a clinical study of male children 8 to 12 years with ADHD, L-theanine improved sleep.

If you or your child has sleep issues, please reach out to your healthcare provider.

It's essential to evaluate and rule out contributing issues such as:

  • Anxiety
  • Sleep apnea
  • Restless legs syndrome
  • Insomnia
  • Iron deficiency anemia

Sleep issues can be connected with behavior and mood issues in adults and children.

Your healthcare provider can help you figure out and address the root cause.


Researchers studied theanine for its stress-reducing effects. In young adults, L-theanine reduced stress. It also lowered blood pressure in high-stress situations.

Further study is needed to confirm these results.

What Are L-Theanine’s Downsides?

L-theanine has been mostly well-tolerated in clinical trials. However, adverse effects or interactions are still possible, including the following:

  • Allergy: People allergic or hypersensitive to tea or any part of L-theanine products should avoid tea or L-theanine. Carefully read your product labels. If you're having a severe allergic reaction to L-theanine, symptoms may include breathing difficulties, itchiness, and rash. Call 911 and seek prompt medical attention if you have a severe allergic reaction or life-threatening symptoms.
  • Anxiety medications: Theanine reduced anxiety in a clinical study. Theoretically, it may interact with medications or other supplements used for anxiety.
  • Blood pressure medication: Theanine has lowered blood pressure in clinic study. Theoretically, it may interact with medications or other supplements that affect blood pressure.
  • Cancer medication: Using L-theanine supplements while undergoing chemotherapy is best done in collaboration with your healthcare provider.
  • Pregnancy or breastfeeding: Pregnant or breastfeeding people should likely avoid L-theanine supplements. Speak with your healthcare provider or pharmacist for further information.

Dietary supplements are not regulated like prescription medications in the United States. Therefore, some may be safer than others. When choosing a supplement, consider factors such as third-party testing, potential drug interactions, and other safety concerns. Talk to a healthcare provider or a registered dietitian nutritionist (RD or RDN) about supplement quality and safety.

How Does L-Theanine Work?

Researchers believe L-theanine improves sleep quality via anxiolysis (reducing anxiety), not sedation.

Scientists believe these effects may be due to theanine's ability to benefit levels of the following:

  • Glutamate
  • GABA (gamma-aminobutyric acid)
  • Serotonin
  • Dopamine
  • Alpha-wave brain activity

L-theanine also impacted levels of the following when used with antipsychotic medication:

  • Dehydroepiandrosterone (DHEA)
  • DHEA's sulfate (DHEAS)
  • Cortisol
  • Brain-derived neurotrophic factor (BDNF)

Researchers think BDNF may help the brain heal itself, which may explain some of theanine's positive benefits.


Always speak with a healthcare provider before taking a supplement to ensure that the supplement and dosage are appropriate for your individual needs.

L-theanine is available in the following forms:

  • Capsule
  • Gummy
  • Liquid
  • Powder
  • Soft gel
  • Tablet

Theanine is also found in tea. It's often combined with other ingredients. Vegetarian and vegan products are available.

The following are dosages used in clinical studies. They are not meant to substitute for a consultation with your or your child's healthcare provider:

  • ADHD: In male children (8 to 12 years), 2.5 milligrams per kilogram (mg/kg) of body weight of L-theanine for six weeks was studied.
  • Anxiety: In adults, 200 to 400 milligrams (mg) of L-theanine daily for up to eight weeks were studied.
  • Cognition: In adults, 100 to 400 mg L-theanine for auditory processing was tested, with 400 mg producing the highest results. In young adults, 97 mg of L-theanine with 40 mg of caffeine helped attention. (The AACAP advises against caffeine for children under 12 years.)
  • Depression: A dose of 250 mg of L-theanine taken daily along with a prescribed antidepressant for eight weeks was tested.
  • Schizophrenia: From 250 to 400 mg of L-theanine taken daily with regularly prescribed medication for up to eight weeks was studied.
  • Sleep: In adults, 200 mg per day of L-theanine for four weeks was studied. In children with ADHD-related sleep disturbances, 400 mg daily for six weeks split into two daily doses were tested.
  • Stress: Theanine at doses as low as 50 mg increased relaxation. For adults, 200 to 400 mg daily L-theanine for up to eight weeks. For young adults, 200 mg of L-theanine were tested.

Dietary supplements are not regulated the way drugs are in the United States, meaning the Food and Drug Administration (FDA) does not approve them for safety and effectiveness before products are marketed. Whenever possible, choose a supplement tested by a trusted third party, such as the U.S. Pharmacopeia (USP), ConsumerLab.com, or NSF.org. However, even if supplements are third-party tested, they are not necessarily safe for all or effective in general. Therefore, talking to your healthcare provider about any supplements you plan to take and asking about potential interactions with other supplements or medications is essential.

Similar Supplements

Supplements with anxiety-lowering and/or sleep-inducing effects include but aren't limited to the following:

  • Ashwagandha
  • Cannabidiol (CBD)
  • German chamomile
  • Kava
  • Lemon balm
  • Magnesium
  • Melatonin
  • Passionflower
  • Valerian

Physical activity, including but not limited to aerobic exercise and yoga, lowers stress levels and can improve sleep.

Acupuncture has also been touted for its anxiety-lowering and sleep-inducing effects.


Since its discovery in the 1940s, researchers have investigated L-theanine for ADHD, anxiety, cognition, stress, and more.

While results are promising, more research is needed.

Consider avoiding L-theanine in the following situations:

  • Pregnancy
  • Breastfeeding
  • Chemotherapy

And please do your best to speak with your healthcare provider, registered dietitian nutritionist (RD or RDN), and/or pharmacist about your supplements, prescriptions, and over-the-counter medication.

This way, you can collaboratively come up with a plan that optimizes safety and helps successfully meet your health goals.

Frequently Asked Questions

  • What is L-theanine?

    L-theanine is an amino acid found in tea and some mushroom species.

  • What does L-theanine do?

    Clinical studies suggest L-theanine has antianxiety effects and promotes relaxation, sleep, and cognitive function.

  • How much L-theanine is in green tea?

    One study suggested the L-theanine content of green tea was 6.56 milligrams per gram (mg/g) of tea leaves. Conversely, white tea had 6.26 mg/g, oolong 6.09 mg/g, and black 5.13 mg/g. Anywhere from 1 to 3 g of tea have been used per cup. This means a cup of green tea may have anywhere from around 6.5 to 19.5 mg of L-theanine.

L-Theanine: Everything You Need To Know (2024)


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