100–200 mg; with caffeine (≈2:1) for a calm focus.
Reduces stress and promotes calm without sedation.
View the study (systematic review) →Improves attention and softens the jitteriness of caffeine.
View the study (clinical trial) →200–400 mg 30-60 min before the feared situation (presentation, exam, public speaking): reduces reactive cortisol and anticipatory anxiety without sedation.
View the study (clinical trial) →4 weeks of 200 mg/day lowered salivary cortisol and perceived stress scores in stressed students/workers.
See the study (4-week RCT) →⏱ 3 min read
L-theanine is an amino acid found almost exclusively in green tea and some edible mushrooms, largely responsible for the characteristic umami flavor of the best-quality tea leaves and, probably, for the subjective effect of “alert relaxation” that distinguishes green tea from other caffeinated drinks; structurally it is an analog of glutamate and GABA, which allows it to cross the blood-brain barrier easily and modulate several neurotransmission systems without sedating or stimulating.
In the brain, L-theanine moderately increases alpha-wave activity measured by electroencephalogram, a pattern associated with states of wakeful relaxation similar to those produced by meditation or deep concentration; it also modulates levels of GABA, dopamine, and serotonin, which makes it one of the few compounds capable of producing a state of calm without losing mental sharpness, exactly the opposite of what benzodiazepines do.
In people with mild to moderate clinical anxiety, several randomized trials have shown significant improvements on standardized anxiety scales at doses of 200 to 400 milligrams per day for 4 to 8 weeks; the subjective effect appears 30-60 minutes after taking it (acute effect) and intensifies with prolonged use, which makes it a reasonable tool for occasional stressful situations and for sustained use in people with background anxiety.
In students during exams, professionals giving public presentations, or people in evaluative situations, L-theanine at a dose of 200 milligrams one hour beforehand reduces the subjective sensation of stress, improves some physiological markers (heart rate variability), and maintains cognitive performance without the sedative effect of classic pharmacological anxiolytics.
The combination of L-theanine and caffeine is one of the most interesting discoveries of modern nootropics: 100 to 200 milligrams of L-theanine with 50 to 100 milligrams of caffeine improve sustained attention, reaction speed, and accuracy on cognitive tasks more than either one alone, without the jitteriness or anxiety that caffeine alone can cause in sensitive people.
This synergy explains why green tea has such a different subjective profile from coffee even though both contain caffeine: the natural proportion of L-theanine in tea (about 20 mg per cup) modulates the effects of caffeine (30-50 mg per cup of green tea) and produces the characteristic state of “calm alertness” that Japanese culture has celebrated for centuries.
In mild insomnia, L-theanine at doses of 200-400 milligrams before bedtime improves subjective sleep quality without acting as a sedative, which is probably associated with a reduction in the nighttime mental rumination and anticipatory anxiety that many people with insomnia report; it is not as effective a tool as melatonin for circadian phase problems or valerian for severe insomnia, but its non-sedating profile makes it attractive for people who do not want the morning grogginess typical of hypnotics.
The doses studied range from 100 to 400 milligrams per day, divided into one to three doses depending on the goal (a single 200 mg bolus before a stressful situation, divided doses with caffeine for prolonged concentration, a nighttime dose for sleep); it can be taken with or without food without a significant loss of absorption.
It has an exceptionally good safety profile: virtually no adverse effects at the doses studied, no specific contraindications beyond pregnancy (where data are limited but no significant problems have been described), and no relevant documented drug interactions; people taking antihypertensives may experience a small additional drop in blood pressure, a minor precaution but one worth keeping in mind in treated hypertensive patients.
Information, not medical advice. Scientific evidence reflects the quality of the studies.