Our evidence-based analysis of L-Theanine features unique references to scientific papers and anecdotal reports.

What Is L-Theanine?

L-Theanine is a unique amino acid present in ordinary tea leaves that has been proven to relax the mind without causing drowsiness.‍[1]

When taken in combination with caffeine, L-theanine may relieve depression, enhance memory, focus, and overall cognitive performance.‍[2]

L-Theanine is a recognized anxiolytic (anxiety reducer) that has been shown to improve the quality of sleep and positively affect both mental and physical stress symptoms by inducing a feeling of calmness and reducing heart rate and blood pressure.‍[3]

Unlike some other natural anxiolytics such as valerian and hops, L-theanine does not act as a sedative that depresses central nervous system activity; on the contrary, it works by boosting levels of calming brain chemicals.

Studies show that it has enormous potential as a neuroprotectant that can help prevent oxidative damage in the brain,‍[4] and may even help offset the cognitive decline associated with aging.‍[5]

Benefits and Effects of L-Theanine

L-Theanine provides a surprising array of benefits that can have positive effects both physically and mentally.

Reduces Stress and Anxiety

L-Theanine’s ability to reduce anxiety, offset the physical effects of stress, and enhance feelings of calmness are among its most well-known benefits and are no doubt in large part responsible for the enduring global popularity of tea (which is the second most popular drink in the world after water).‍[6]

Studies show that L-theanine effectively reduces concentrations of cortisol, often referred to as “the stress hormone,”‍[7] reduces both psychological and physiological stress responses,‍[8] and promotes alert relaxation.‍[9]

Improves Memory, Attention, and Mood

L-Theanine’s calming effects may have various benefits, including boosting attention, focus, and learning ability through sensorimotor gating, or filtering environmental stimuli to prevent an overload of irrelevant information in the higher cortical centers of the brain.‍[10]

Studies show that this “gating” effect reduces distraction and improves cognitive alertness, increasing the ability to focus and enhancing overall cognitive efficiency.‍[11]

L-Theanine is particularly effective as a nootropic when taken in combination with caffeine.‍[12]

Combining the two eliminates the vasoconstrictive effect and behavioral effects of caffeine, thus improving cerebral blood flow and enhancing cognition and mood.‍[13]

The L-theanine–caffeine combination has also been shown to improve memory and selective attention and increase brain theta waves, which are an indication of cognitive alertness.‍[14]

Improves Sleep

Research indicates that L-theanine is a safe, natural sleep aid that works by reducing anxiety as opposed to sedation.‍[15]

L-Theanine has been shown to improve both the ability to fall asleep and the quality of sleep itself without causing daytime drowsiness or other negative side effects.‍[16]

Reduces Blood Pressure

Oral administration of L-theanine has been shown to substantially lower both systolic and diastolic blood pressure. This effect was particularly pronounced among “high response” participants who demonstrated a significant rise in blood pressure in response to psychological stress.‍[17]

Caffeine has been shown to elevate blood pressure during stress,‍[18] but when taken in combination with L-theanine, caffeine did not increase blood pressure.

Because repeated temporary stress-related blood pressure elevation can lead to hypertension, L-theanine is believed to have some potential as a hypertension preventative for young adults who show a large blood-pressure response to psychological stress.

Improves the Effectiveness of Cancer Treatment

Research suggests that L-theanine may be a valuable adjunct therapy for cancer treatment.

Both human trials and animal studies show that theanine suppressed the growth of lung cancer and leukemia cells, enhanced the anticancer activity of cancer treatments such as trichostatin, and reduced cancer cell migration and invasion.‍[19]

Research also suggests that L-theanine could be used as an effective chemopreventive agent for cancer.‍[20]

How It Works

L-Theanine works primarily by modulating various brain chemicals, increasing the levels of inhibitory neurotransmitters and actively blocking the overproduction of excitatory neurotransmitters.‍[21]

L-Theanine’s chemical structure is similar to that of glutamate, the most important excitatory neurotransmitter, and that similarity enables it to bind to and block glutamate receptors in the brain. This effectively lowers glutamate levels and prevents glutamate receptor overactivity that is typically triggered by stress, resulting in increased calm and relaxation.‍[22]

L-Theanine also increases levels of the calmative neurotransmitters dopamine, serotonin, and GABA, all of which are important for regulating mood, alertness, sleep, and energy. At the same time, it suppresses overproduction of the potentially damaging stress-related hormone cortisol and triggers the release of Alpha waves, a state of brain activity associated with wakeful relaxation.‍[23]

L-Theanine is a water-soluble amino acid that is metabolized in the kidneys and readily crosses the blood-brain barrier. It reaches maximum concentrations in the brain in less than an hour.


L-Theanine has been shown to interact positively with caffeine,‍[24] and is often taken with caffeine in a 2:1 ratio, particularly when used as a cognitive enhancer. Doses of 100–200 mg L-theanine and 50–100 mg caffeine are considered typical and are generally both effective and well tolerated.

Those who are unaccustomed or particularly sensitive to caffeine may want to reduce the amount of caffeine taken with each dose or omit it entirely.


L-Theanine boosts focus and enhances relaxation on its own but is most effective when combined, or “stacked,” with other nootropics.

L-Theanine and Caffeine Stack

L-Theanine improves cognitive performance and subjective alertness when “stacked,” or combined, with caffeine.‍[25]

L-Theanine can take away the jitteriness often associated with caffeine, leaving a relaxed but alert state that’s perfect for productivity.

The benefits of stacking L-theanine with caffeine may include:

  • Improved memory
  • Enhanced focus
  • Increased motivation
  • Boosted mood
  • Reduced anxiety

Stacking L-theanine with caffeine is one of the most popular choices among those looking for a cognitive boost due to its simplicity, low cost, and effectiveness.

The combination is best taken only when an energy boost is needed, as opposed to daily, to avoid building up a tolerance.

Maximum 1x–2x per day

NOTE: For a convenient way to take this stack, we recommend getting caffeine + L-theanine capsules from PureNootropics.net

L-Theanine Stack for Universal Cognitive Enhancement

For a preformulated nootropic that contains a blend of 11 cognitive enhancing supplements, including L-theanine, designed to optimize a wide array of cognitive functions, we recommend Mind Lab Pro.

Mind Lab Pro’s strategy aims at all aspects of memory, mental performance, mood and stress resistance, and brain repair, and maintenance. Their combination of nootropics is designed to affect brain energy, neurotransmitters, brain blood flow, brain waves, neuroprotection, and regeneration.

Read our Mind Lab Pro review for a detailed overview.

Side Effects

L-Theanine is considered extremely safe and has been designated as a GRAS (Generally Recognized as Safe) ingredient by the US Food and Drug Administration.‍[26]

In animal testing, even very high dosages continued over prolonged periods failed to produce toxicity or carcinogenicity.‍[27]

There are no documented serious L-theanine side effects.

Minor side effects, including dizziness and headache, are infrequently reported when L-theanine is taken in combination with caffeine.

Where to Buy

If you’d like to buy L-theanine, we recommend:

For L-theanine combined with caffeine, we recommend:

Alternatively, if you’d like to take a supplement that contains a blend of 11 cognitive enhancing nootropics, including L-theanine, we recommend Mind Lab Pro. Read our Mind Lab Pro review for a detailed overview.

Closing Thoughts

L-Theanine is a natural and safe amino acid that offers a surprisingly broad range of benefits.

It has been shown to ease anxiety, improve sleep, enhance cognition, memory, focus, and protect the brain. But that’s only part of the L-theanine picture; research indicates that it can help reduce and might prevent stress-related hypertension, and it may be a valuable adjunct therapy for cancer patients.

If you’re interested in an effective natural nootropic that has no documented serious side effects, L-theanine may be worth a try.


Planning to start a new supplementation regimen? See our medical disclaimer.

This page was last updated on July 16, 2021.