L-theanine is an amino acid that is not commonly found naturally in food. It’s not one of the essential amino acids (an amino acid that our bodies cannot produce) nor is it even one of the common nonessential amino acids.

What is L-theanine?

L-theanine is an amino acid that is extracted from the leaves of Camellia sinensis, commonly referred to as “tea plant”. It can be found in both green and black teas, as well as in Bay Bolete mushrooms, in small amounts. (14)

Research indicates that L-theanine promotes relaxation without inducing sedative effects. It may help to achieve a relaxed mental state and slightly improve attention. (14)

Let’s take a closer look at L-theanine, including its potential benefits and risks.

What does L-theanine do?

L-theanine promotes relaxation without drowsiness by contributing to a number of changes in the brain.

Boosts levels of calming brain chemicals

L-theanine increases levels of the neurotransmitters serotonin, dopamine, and GABA. (8)(13) Neurotransmitters are chemical messengers that transport signals from nerve cells to other cells in the body. These neurotransmitters, in particular, play a role in regulating emotions, mood, concentration, alertness, and sleep, as well as appetite, energy, and other cognitive skills. (1)(9)(11)

Enhances alpha brain waves

Alpha brain waves are dominant during relaxation thoughts and in some meditative states. (7) L-theanine appears to promote the emission of alpha brain waves, which aid in overall mental coordination, calmness, alertness, mind/body integration, and learning. (5)

Research indicates that L-theanine promotes relaxation without drowsiness.

L-theanine benefits

Research has shown that L-theanine may have many health benefits, including improved relaxation, focus, sleep quality, and blood pressure levels.

Increased relaxation

As previously mentioned, L-theanine may affect alpha waves, which are associated with mental relaxation.

A 2003 study evaluated the effect of L-theanine on the release of brain alpha, a surrogate marker for mental relaxation. Researchers found that males aged 18 to 30 years with high anxiety who received L-theanine supplementation had a greater release of alpha waves, which the authors associated with increased mental relaxation. (15)

Additionally, 200 mg of L-theanine has been reported to reduce resting heart rate, further highlighting its relaxing properties. (4)

Reduced stress and anxiety

L-theanine is believed to possess anxiolytic (anxiety reducing) properties. L-theanine has positive effects on both the mental and physical symptoms of stress, including reducing heart rate and blood pressure. (4)

A study using a mental arithmetic task as an acute stressor found that participants supplementing with L-theanine had a lower heart rate and reduced sympathetic nervous system activation in response to the task. Authors suggest that L-theanine could produce an anti-stress effect by lowering levels of excitatory brain chemicals, such as glutamate. (4)

Increased focus and attention

Research demonstrates that L-theanine can increase attention span and reaction time in people who are prone to anxiety. One study found that individuals with a high anxiety propensity taking 200 mg of L-theanine had a lower heart rate, higher visual attention, and improved reaction time compared to those taking a placebo. (3)

L-theanine may help to increase focus

Additionally, when paired with caffeine, L-theanine may also help increase focus and attention. A 2010 study found that 97 mg of L-theanine taken in combination with 40 mg of caffeine improved attention in young adults during a demanding cognitive task. Participants in the study also reported feeling more alert and less tired in general. (2)

Improved sleep quality

The hormone melatonin is well known for its role in controlling your sleep and wake cycles. (12) Research suggests that L-theanine could also be beneficial for a good night’s sleep.

Several studies have reported that the administration of 250 mg to 400 mg of L-theanine improves sleep quality in both animal and human trials, including individuals with schizophrenia. (16)

Another study suggests that L-theanine may represent a safe and important adjunctive therapy in childhood attention-deficit/hyperactivity disorder (ADHD). Researchers examined the effects of 400 mg of L-theanine daily on a group of eight to 12-year-old boys compared to a placebo. After six weeks, the boys taking L-theanine experienced longer and more restful sleep. However, the authors also note that longer term studies examining the wider therapeutic role of L-theanine are needed before it can be proven safe and effective in children. (10)

Blood pressure control

L-theanine may be beneficial for individuals with a tendency for elevated blood pressure during stressful situations.

A 2012 study found that individuals whose blood pressure increased more than average in response to performing a mental task experienced significant reductions in blood pressure following a mental task when taking L-theanine. Authors suggest that L-theanine might be useful to help attenuate elevated blood pressure in adults with a greater stress response. (17)

L-theanine side effects

L-theanine is generally well tolerated by healthy adults. Doses of L-theanine up to 400 mg have been safely taken for a period of eight weeks. Mild adverse side effects such as headache and sleepiness have been reported. (6)

Special precautions

Precautions should be taken in some special populations, including children, pregnant or breastfeeding women, and individuals prone to low blood pressure.

There is not enough reliable information about the safety of L-theanine taken during pregnancy or breastfeeding. For this reason, it is suggested to avoid use. (6)

L-theanine is likely safe for children. Doses of 200 mg have been safely used twice daily for up to six weeks in boys aged 8 to 12 years, however more research is required to make a definitive conclusion and careful consideration is needed prior to administration. (6)

L-theanine might lower blood pressure, therefore, people who are prone to low blood pressure should exert caution. (6)

The bottom line

L-theanine has been shown to improve relaxation, sleep, anxiety, and attention. Due to the lack of conclusive research, a safe L-theanine dosage recommendation is not known. However, L-theanine is generally regarded as safe for consumption.

If you’re getting this compound from tea, following general caffeine consumption guidelines can be helpful. For those considering taking an L-theanine supplement, it is best to consult with your integrative healthcare practitioner, who can provide you with the individualized guidance and dosing.

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  2. Giesbrecht, T., Rycroft, J. A., Rowson, M. J., & De Bruin, E. A. (2010). The combination of L-theanine and caffeine improves cognitive performance and increases subjective alertness. Nutritional neuroscience, 13(6), 283–290.
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