Traditional uses
Tea has been historically consumed for benefits to mood and performance.1
L-theanine is a water-soluble amino acid found mainly in various tea plants, and can be found in different parts of the plant, such as the roots, shoots, and leaves.2
Mechanism of Action
L-theanine helps reduce symptoms related to stress, depression, anxiety, and sleep disturbance,3 as well as supports cognitive function and attention.4
It can cross the blood–brain barrier and may increase alpha-brain waves5, which can increase relaxation while maintaining alertness. It can elevate central GABA, dopamine, serotonin levels,6 which can lead to mood stabilization. L-theanine is also a partial agonist on the glycine binding site of N-methyl-D-aspartate (NMDA) receptors, alluding to the substance’s potential to modulate excitatory neurotransmission.7
L-theanine has several other benefits, including anti-inflammatory and antioxidant. It has been found to mitigate expression of NF-κB and the pro-inflammatory cytokines of IL-1 and IL-6, while encouraging expression of IL-10, an anti-inflammatory cytokine. It has been shown to mitigate profibrotic mediators (including connective tissue growth factor and transforming growth factor β) while also promoting expression of the fibrinolytic enzyme metalloproteinases-13. The anti-fibrotic effect, along with L-theanine’s demonstrated ability to decrease elevated serum aspartate aminotransferase (AST) and alanine aminotransferase (ALT), indicate potential support for protection of the liver.2
Its neuroprotective effects include enhancing cognition and memory, as well as aiding in neuropathy prevention and nerve repair. It is cardiovascular protective in that it helps to reduce vascular remodeling and decrease circadian rhythm disruption. It supports immune regulation by balancing Th1 / Th2 cytokines and enhancing intestinal mucosal immunity.2
Evidence-based research
In a placebo-controlled, double-blind, randomized trial of 95 patients diagnosed with Obsessive Compulsive Disorder (OCD), the combination of L-theanine and fluvoxamine treatment showed significantly more improvement in obsession scores than fluvoxamine plus placebo treatment.8
In a randomized, placebo-controlled, crossover, double-blind trial, 30 participants without any major psychiatric illnesses were given L-theanine (200mg/day) or placebo for 4 weeks. Sleep latency and disturbance, as well as use of sleep medication were reduced in the L-theanine group compared to placebo. Verbal fluency, particularly letter fluency, also improved in the L-theanine group, compared to placebo. The study’s findings suggested benefit to the mental health of the general population regarding stress-related and cognitive challenges.9
In a study comprised of 30 healthy adults with moderate stress and randomized to an L-theanine supplement (400mg/day) or placebo for 28 days, L-theanine decreased stress and light sleep, increased quality of sleep, improved cognitive attention, and was found to be safe.10
Mouse models have demonstrated L-theanine’s improvement of phenobarbital sodium’s anticonvulsive effect, and its ability prevent brain atrophy in senescence-accelerated models. An adolescent male rat model showed its ability to prevent development of cognitive and emotional abnormalities associated with THC exposure.2
Safety in Pregnancy
Safety in pregnancy has yet to be studied in human clinical trials. However, in a gestational obesity pregnant mouse model, L-theanine was shown to ameliorate adverse pregnancy outcomes by attenuating adiposity, metabolic markers, weight gain, gut barrier dysfunction, and placental tissue junction zone abnormalities.11
Dosage and General Safety
Clinical indications for L-theanine include situational anxiety (e.g. in office/clinic presentation), and supporting mindfulness/meditation practices.
L-theanine daily doses of 200–400mg for up to 8 weeks have been considered safe. Though longer term studies have yet to be conducted,12 longer term clinical uses have been found to be safe.