Also known as: Theanine, Suntheanine, gamma-glutamylethylamide, Green tea amino acid
Cognitive & NootropicGood evidence
An amino acid found almost exclusively in tea, valued for producing calm alertness without sedation. Its most reliable application is alongside caffeine, where it appears to smooth the jitteriness while preserving the focus.
Typical dose
100.0–200.0 mg per day
30-60 minutes before the task; with caffeine, take together
What it is
L-theanine is a non-protein amino acid found almost exclusively in tea leaves and in a single species of mushroom. It accounts for much of the savoury umami character of good green tea, and is the compound most often credited with the difference between the feeling of tea and the feeling of coffee.
A typical cup of green tea supplies somewhere in the region of 25-60 mg, meaning supplemental doses of 100-200 mg represent several cups' worth in a single serving.
Most quality supplements use a fermentation-derived L-theanine. The L-isomer is the biologically relevant form; racemic mixtures containing D-theanine are less desirable, so specified L-theanine rather than unspecified theanine is worth looking for on a label.
How it works
L-theanine crosses the blood-brain barrier readily. Its most consistently observed effect is an increase in alpha wave activity, the electrical pattern associated with wakeful relaxation, the state of being alert without being agitated. This is measurable by EEG and is among the more reproducible findings for any nootropic.
Structurally similar to glutamate, it interacts with glutamate receptors and appears to modulate excitatory signalling. It has also been reported to influence GABA, dopamine and serotonin, though these findings are less consistent than the alpha wave data.
The synergy with caffeine is the most practically useful part. Caffeine increases arousal, sometimes past the point of usefulness into jitteriness and anxiety. Theanine appears to attenuate that overshoot without cancelling the alertness, which is why the pairing is more reliable than either compound alone for sustained focus.
What the evidence shows
The caffeine and theanine combination has the strongest support. Multiple controlled trials have reported improvements in attention, task-switching and reduced susceptibility to distraction when the two are taken together, with effects generally clearer than for theanine alone.
For stress measures, trials have reported reductions in subjective stress and in physiological stress markers, particularly under acute pressure. Effects are modest and more evident in people who start out more wound up.
Sleep research is a growing area, with the interesting finding that theanine appears to improve sleep quality without knocking you out, likely by reducing pre-sleep arousal rather than inducing sleep. Overall the evidence is reasonable for a nootropic, with the important caveat that effect sizes are modest throughout.
Dosing
Typical effective dose is 100-200 mg. Trials have used up to 400 mg without difficulty, but most benefit appears within the lower range.
With caffeine, a ratio of roughly 2:1 theanine to caffeine is the common convention, for example 200 mg theanine with 100 mg caffeine. Some people prefer 1:1 at higher caffeine doses. This pairing is the single most reliable way to use it.
Onset is quick, typically 30-60 minutes, and it does not require loading or daily consistency to work. For sleep, 200 mg an hour before bed is the usual approach, though it is better understood as reducing mental arousal than as a sleep aid.
At a glance
Common forms
L-theanine powder, Suntheanine, Capsules, Combined with caffeine, Green tea extract (low dose)
Half-life / duration
Plasma half-life approximately 1-3 hours; effects felt within the hour
Timing
30-60 minutes before the task; with caffeine, take together
Competition status
Permitted — not on the WADA Prohibited List
Category
Cognitive & Nootropic
Safety and side effects
L-theanine has an excellent safety record. It has been consumed in tea for centuries and trials at supplemental doses report very few adverse effects. Headache and mild drowsiness are the occasional complaints.
It does not appear to produce dependence, tolerance or withdrawal, and does not impair cognitive or motor performance the way things that knock you out do. This combination of gentleness and measurable effect is unusual.
Because it may modestly lower blood pressure, take care if yours is being managed, and check before use if you take regular medication.
Who should avoid it
Take care if your blood pressure is being managed. Speak to your doctor before use if you take regular medication, particularly anything affecting sleep or alertness. Not established for use in pregnancy or breastfeeding.
This entry is provided for information only. Food supplements should not be used as a substitute for a varied and balanced diet and a healthy lifestyle. Consult a qualified healthcare professional before use if you are pregnant, breastfeeding, taking medication or under medical supervision.
