L-Theanine is part of our FOCUS + STRESS relieving categories.

L-Theanine: Benefits, Side-effects, dosage and summary

Last Updated: May 1, 2022

Overview | The Best L-Theanine Supplements | Benefits | Relaxation | Anxiety | SleepImmunityHow to buy | Dosage | How to take | Side effects | The bottom line

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The amino acid L-Theanine is found in green and black tea. L-Theanine content in green tea is the highest found in nature. There is evidence that matcha may have higher concentrations of l-theanine than green tea.

It is also found in trace amounts in a mushroom known as the bay bolete.

L-Theanine is able to cross the blood-brain barrier to exert its effects on our mental state.

The Best L-Theanine Supplements

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We recommend Nootropics Depot L-Theanine as they have high standards for impurities – alternatively any Suntheanine product should be taken (patented)

L-Theanine should be taken prior to sleep, and not in the morning unless combined with caffeine as in tea or coffee. If you drink coffee, L-theanine can be used in conjunction to remove any associated jitters and crash.

How it works

L-theanine works in a number of ways to enhance our brain and health.

It targets certain pathways in the brain that improve our senses of attention, pleasure and arousal. At the same time, L-theanine reduces anxiety and improves focus.

L-theanine works in the brain to do this by:

1. Increasing alpha brain waves – which are tied to our sense of relaxation and helps us to concentrate [1].

This effect is enhanced synergistically as L-theanine reduces our response to stressful events [2].

2. Increasing the activity of  numerous neurotransmitters. L-theanine increases serotonin, GABA and dopamine levels creating a neuroprotective effect for brain health [3][4][5].

These increases in GABA expression may lead to deeper and longer sleep [6].

3. L-theanine supplementation interferes with l-glutamate pathways in the body [7]. L-theanine stops the binding of L-glutamic acid to glutamate receptors in the brain. Glutamate has been linked to oxidative stress-induced damage to the brain. A single cup of tea can reduce glutamate uptake [7].

4. L-theanine attenuates our sympathetic nervous system and minimises cortical neuron excitation. In other words, it makes us less reactive to stressful events so we can deal with them effectively [8]. For example, 200-350mg L-theanine intake appears to reduce heart rate response when exposed to stress compared to placebo.


The benefits of L-theanine are numerous and it works in a variety of ways to improve our general health. These include:

1. L-Theanine and relaxation

The reason that L-theanine is promising is that it notably increases relaxation without any drowsiness, within 30 minutes to one hour.

A systematic review of five trials including 104 participants, had four studies suggest that L-theanine promoted relaxation [9]

L-theanine also appears to reduce blood pressure which means it should not be taken with certain medications including ACE inhibitors [10][11].

2. Improves anxiety and attention

L-Theanine may ameliorate attention problems in those who exhibit symptoms of anxiety [12][13].

L-Theanine is promising when used to improve reaction time.

A dosage of 200mg 15-60min prior to an attention test resulted in a pronounced effect on attention performance and reaction time response in anxious subjects [13].

However, these benefits are insignificant when it comes to subjects with minimal anxiety.

3. May improve sleep

Many people of all ages struggle to get the recommended 7-9 hours of sleep every night.

L-Theanine is promising in treating this issue.

Studies have shown that green tea is positively associated with sleep quality in older people [14][15][16]. Those who had the best quality sleep also drank the highest quantities of tea. This effect was significant when the tea used had lower caffeine content. Taking L-theanine may provide best results.

A quality randomized double-blind, placebo-controlled study found that in children with ADHD a dose of 400 mg/d L-theanine (Suntheanine) was tolerated and safe whilst improving sleep percentage and efficiency [17].

As disturbed sleep is correlated to ADHD prevalence, L-Theanine may be helpful to nudge you towards optimal sleep. Andrew Huberman suggests a dose of 100-400mg L-Theanine.

4. May improve athletic recovery

Maximal physical exercise often impairs the immune system due to the decrease in immune cells (lymphocytes) and increase in neutrophils.

This results in systemic inflammation and immunosuppression that runs counter to our general health.

However, supplementing L-theanine can reduce these effects.

Olympic rowers given L-theanine for 6 weeks had a significant post-exercise decrease in inflammatory marker (interleukin-10) and a decrease in cytotoxic lymphocytes [18].

A study of long-distance runners indicated a significant increase in inflammatory marker (C-reactive protein) and neutrophil count from L-Theanine and cysteine. Heightened inflammation may cause a multitude of health issues such as fatty liver disease, diabetes and IBD.

However, subjects given a mixture of L-Theanine and cysteine for 10 days prior to training camp had no increase in harmful markers. When performing intensive exercise, the ingestion of theanine may be useful in preventing a loss of immunity, and may reduce symptoms in the event of sickness [19].

A randomised, double-blind, and placebo-controlled study found that L-Theanine helped prevent colds [20].

A randomised controlled trial of 200 healthcare workers for 5 months determined L-Theanine was useful in preventing flu [21].

How to buy

Our first recommendation is for products containing Suntheanine. This compound is produced by Taiyo Kagaku Corporation. Suntheanine is a patented form of L-theanine produced in Japan. Most brands market Suntheanine under their own product line. On iHerb, brands that carry Suntheanine include Sports Research, Doctor’s Best and Source Naturals, in fact numerous brands use this formula.

As an alternative, we recommend Nootropics Depot L-Theanine as they third party test for impurities.


Most L-Theanine supplements come in 100 mg tablets. Typically, 100-200mg is taken for adults.  Others take up to 600mg per day but this is on the higher end.

Children should take less, and 400mg has been safely used in a study of 98 children for six weeks.

Maximising L-Theanine Extraction

To get L-Theanine from green tea leaves is as simple as brewing a cup of tea.

For maximum extraction, green tea should be prepared using water at temperatures of 178 degrees fahrenheit for 30 minutes.

A tea particle size of 0.5-1mm combined with water-to-tea ratio of 20:1 provides the optimum level of L-Theanine.

L-Theanine intake should be limited in the morning and early afternoon in supplement form. This is because it activates GABA which is an inhibitory neurotransmitter [22].

Side effects

L-Theanine side effects are minimal at doses below 600mg per day.

The side effects of L-Theanine are rare and it is generally well tolerated.

L-Theanine may lower blood pressure and people with low blood pressure should consult their physician.

Effects may include headache, digestive issues or sleep disturbances.

The Bottom Line

L-Theanine is promising due to its ability to lower anxiety and promote relaxation and focus.

People of all ages can benefit from L-theanine, including children with ADHD or attention issues. Athletes in particular may benefit from the anti-inflammatory effects of drinking tea.

Doses of 100-200mg have been shown to be effective however higher doses (400mg) may be better for sleep.



L-Theanine is best taken at night, around 1 hour before sleep.

Most supplement companies sell L-Theanine in 100mg doses – and brain benefits have been shown in doses of around 100-400mg.

It works quickly, within 30-60 minutes.

There are minimal side effects.