- N-ethylglutamic acid
For Patients & Caregivers
How It Works
L-theanine may be helpful to improve sleep quality, but larger studies are needed to confirm safety and effectiveness in patients with various conditions.
L-theanine is an amino acid found in green tea. A population study suggests that consuming green tea may help reduce stroke risk, but it is unclear whether L-theanine contributed to this benefit. L-theanine may help improve sleep and reduce stress, but larger well-designed trials are needed to confirm this effect.
Lab experiments that suggest L-theanine may increase efficiency of chemotherapy drugs or reduce side effects have not been confirmed in humans. Patients undergoing chemotherapy should discuss the use of L-theanine with their physicians because safety data in cancer patients are lacking, and another component found in green tea called epigallocatechin-3-gallate (EGCG) reduces activity of the chemotherapy drug bortezomib.
To improve sleep
Small studies suggest L-theanine can improve sleep quality, but larger well-designed trials are needed.
To reduce anxiety
Studies on whether L-theanine as add-on therapy can reduce anxiety are mixed. Additional studies are needed.
To prevent or treat cancer
Although lab studies suggest that L-theanine has antitumor properties, human data are lacking.
To reduce stroke risk
Results from a population study done in Japan suggest that green tea consumption may help decrease stroke risk. However, it is unclear if L-theanine in green tea contributed to this benefit.
For Healthcare Professionals
L-theanine is a water soluble amino acid found in green tea and mushrooms. Purified L-theanine is available as an oral dietary supplement, and is used for its perceived antioxidant and relaxant effects (12). Several in vitro and animal studies suggest lipid-lowering (1), neuroprotective (2) (16), antiobesity (3), and antitumor (1) (23) properties. Other lab studies suggest L-theanine may affect levels of some neurotransmitters (10) (11), prevent beta-amyloid-induced cognitive dysfunction (13), and promote longevity in C. elegans (20).
A few studies have also been conducted in humans. In a double-blind trial of adjunctive L-theanine for generalized anxiety disorder, there were no significant effects on anxiety, although positive effects on sleep were observed (32). Other small trials in patients with various conditions also suggest improvements in sleep quality (18) and possibly depression, anxiety, and cognitive impairments (29), although larger well-designed trials are needed. Some trials evaluating L-theanine with caffeine suggest improvements in cognitive performance (14) (15), although effects observed with caffeine alone in one study were lost with concomitant L-theanine (22). When combined with antipsychotic treatment, L-theanine alleviated anxiety and related symptoms, and improved sleep in patients with schizophrenia (17) (21).
Epidemiological data suggest green tea consumption may contribute to stroke prevention (4), but it is unclear whether L-theanine alone may confer this benefit.
Preclinical studies suggest L-theanine enhances chemotherapeutic effects of doxorubicin (5) and idarubicin (6), and alleviates adverse effects from use of these agents (7) (24). However, patients undergoing chemotherapy should discuss the use of L-theanine with their physicians because these effects are not based on clinical trials, and epigallocatechin-3-gallate (EGCG) in green tea reduces activity of the chemotherapy drug bortezomib.
Mechanism of Action
As a non-protein amino acid, L-theanine crosses the blood-brain barrier, exerting various neurophysiological and pharmacological effects including: anxiolytic and calming effects, due to inhibitory neurotransmitters and selective serotonin and dopamine modulation; cognitive improvements perhaps through decreased NMDA-dependent CA1 long-term potentiation (LTP) and increased NMDA-independent CA1-LTP; and improved selective attention during mental tasks likely due to changes in alpha brain wave activity (25). Neuroprotective effects are also thought to be due to its selective binding to glutamate receptors (2).
In animal models, L-theanine appears to have a dose-dependent biphasic effect on NSAID-induced gastric ulcers, delaying healing at higher doses (40 mg/kg), but accelerating healing at lower doses (10 mg/kg) perhaps through the maintenance of glutathione levels thus protecting against oxidative damage (26).
In human studies, L-theanine attenuated effects of caffeine on oxygenated hemoglobin, cognition, and mood, suggesting both independent and interactive effects between the two compounds (22). Other studies suggest that combining caffeine and theanine intake causes their individual effects to counteract each other (30) (31). L-theanine also stabilizes glutamatergic concentrations in the brain, which may explain its therapeutic effect in patients with schizophrenia (21).
L-theanine was shown to increase the antitumor activity of chemotherapeutic drugs doxorubicin and idarubicin (5) (6). These agents normally bind the glutamate receptor and the complex is transported across the cell resulting in reduced concentrations, hence attenuating effects of these drugs. Consequent mechanistic studies revealed that L-theanine, a glutamate analogue, competes with glutamate to bind the glutamate receptor, resulting in suppression of chemotherapy efflux (extracellular transport), increasing their concentration (27).
Interestingly, L-theanine also reduces the adverse effects of doxorubicin. The proposed mechanism is based on the variance of glutamate receptors expressed in normal and tumor cells. Whereas theanine binds the glutamate receptor in tumor cells, it is metabolized to glutamate in normal cells. This increase in glutamate likely results in increased efflux of doxorubicin from the cells, thereby decreasing toxicity (28).
Animal models indicate the prevention of doxorubicin-induced acute hepatotoxicity occurs through suppression of intrinsic caspase-3-dependent apoptotic signaling (24). L-theanine does not induce or inhibit cytochrome P450 enzymes (9).
Some novel theanine derivatives were found to inhibit lung tumor growth by targeting EGFR/VEGFR-Akt/NF-kappaB pathways (23).