L-Theanine: Uses, Side Effects, Interactions, and Dosage

what is l-theanine

People have been using L-theanine, or simply, theanine, to relax for thousands of years, in the form of tea.

The origin story of tea goes something like this: A tea leaf fell into a Chinese emperor’s hot cup of water, and he was so intrigued by the smell he took a sip. He loved the flavor, and soon the emperor had all of China’s fanciest folk drinking the stuff.

While that story is likely lore, the relaxing properties of tea are anything but.

Research has shown that L-theanine, a compound commonly found in tea, is proven to act as a relaxing agent.

In this article, we will discuss what l-theanine is, what it does, benefits, dosage and if it is safe.

What is l-theanine?

Theanine is an amino acid that isn’t critical for normal metabolic processes, meaning you’d live just fine without it. People commonly take theanine to promote relaxation, reduce anxiety, and even improve mental performance.

Some people even take theanine to treat attention deficit-hyperactivity disorder (ADHD), reduce high blood pressure, and improve the effectiveness of cancer medication.

However, more research is needed when it comes to its effectiveness in helping with ADHD, blood pressure, and cancer treatment.

What does l-theanine do

The chemical properties of theanine make it uniquely disposed to help:

  • Increase relaxation and reduce anxiety due to its chemical similarity to glutamine.
  • Maintain the brain's level of excitement.
  • Block the binding of L-glutamic acid to glutamate receptors in the brain.

Types of l-theanine

The most common l-theanine used in research studies is called Suntheanine that is produced and patented by Taigo Kagaku. This form of theanine is claimed to be 99% pure is made from a mixture of glutamine with an ethylamine derivative.

L-theanine benefits

L-theanine reduces anxiety & increases attention

It’s the night before a big race. You head to bed early, hoping to catch a full night’s sleep. Suddenly, you’re wide awake and it’s 2 a.m.

Lots of athletes suffer from minor anxiety and sleeplessness the night before an important race or event, often to the detriment of race day performance. Theanine may help those athletes get a sound night’s sleep.

Interestingly, L-theanine reduces feelings of stress while increasing attention. This is remarkable considering that most compounds that increase attention (think caffeine) also increase stress, anxiety, and even insomnia.

L-Theanine promotes sleep

Several studies report that theanine ingestion resulted in improved sleep quality in animal models and in human trials. (Jang, et al.)

Shortly after ingestion, L-theanine affects the brain. It causes people to feel relaxed, but reportedly without causing the “zonked out” feeling of other sleep agents.

It’s more like a relaxing bath versus a full-blown sedative.

L-theanine enhances mental performance

Most research shows that theanine increases mental performance. Taking theanine before a test seems to help reduce errors and taking theanine with caffeine seems to improve task-switching. (Higashiyama, et al.)

L-theanine lowers stress levels

A 2004 study discovered that subjects who consumed 200mg of L-theanine before an anxiety test experienced less stress compared to the placebo group. (Lu, et al.)

A double-blind, counterbalanced study examined theanine’s effects on stress using a mental arithmetic task as an acute stressor. Twelve participants underwent four separate trials.

They took L-theanine at the start of the trial, midway, and two control trials in which they either took a placebo or nothing.

The participants who ingested L-theanine experienced a heart rate reduction and salivary immunoglobulin A (s-IgA) response.

Researchers concluded that ingestion of theanine “could cause anti-stress effects via the inhibition of cortical neuron excitation.” (Kimura K, et al.)

L-theanine lowers cortisol

A 2016 study evaluated the effects of L-theanine on 34 healthy adults in a double-blind, placebo-controlled, balanced crossover study.

They found that stress levels in the L-theanine group were significantly reduced after one hour of treatment, and that cortisol levels were lower in the L-theanine group. ( White, et al.)

L-theanine relaxes the mind without inducing drowsiness

Multiple studies on humans using an electroencephalograph (a machine that measures brain waves) show that L-theanine has a direct effect on the brain.

Researchers found that the chemical significantly increases activity in the alpha frequency band, which indicates that it relaxes the mind without inducing drowsiness. (Juneja et al.)

Effective L-theanine dosage

L-theanine shows effectiveness in doses as little as 50mg, but for best results, L-theanine should be dosed at 100-200mg. 

When to take l-theanine

Theanine and is best consumed 30-60 minutes before bed or in anticipation of a stressful situation.

How long does l-theanine stay in your system?

After ingesting l-theanine is takes ~60 minutes to reach the brain where levels remain elevated for 5 hours. After 24 hours no l-theanine from supplementation is present in the body.

Is L-Theanine safe? Yes!

Currently, there is no research demonstrating that the natural sleep aid theanine has any negative side effects.

Several studies examining theanine toxicity in animals show no adverse effects.

One study conducted a 13-week dietary toxicity and toxicokinetic study in rats. A maximal quantity of 4000 mg/kg weight/day (that’s a lot of theanine!) was administered through dietary integration.

The study found “no consistent, statistically significant treatment-related adverse effects on behavior, morbidity, mortality, body weight, food consumption and efficiency, clinical chemistry, hematology, urinalysis, gross pathology, organ weights or ratios or histopathology.” (Borzelleca, et al.)

L-Theanine side effects

Theanine has not shown any adverse side effects.

L-Theanine interactions with other compounds

Theanine naturally occurs alongside caffeine, and therefore lots of research has been done on how they interact.

Interestingly, some research suggests that the effectiveness of theanine and caffeine is stronger than caffeine alone. (Haskell, et al.)

It has also been shown to “take the edge off” stimulants like caffeine.

Where can I buy L-theanine?

You can find a small dose of L-theanine naturally occurring in most teas.

One study by the University of Bristol found that brewing time greatly impacted the amount of theanine extracted.

They found a standard (200 ml) cup of black tea was found to contain the most l-theanine (24.2 ± 5.7 mg) while a cup of green tea contained the least (7.9 ± 3.8 mg).

To reach an effective dose, you’d have to be a pretty avid tea consumer. L-theanine can also be found at a 200 mg dose in SleepElite.

 About the Author:

michelle stampe spearfush south dakota


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