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Dietary supplements · L-theanine
Young tea shoots, which L-theanine comes from

Young tea shoots, which L-theanine comes from

jaikishan patel · Unsplash

Moderate evidence9 studies
How we rate

“Strong” = several concordant meta-analyses or systematic reviews. “Moderate” = one synthesis, or several controlled trials. “Limited” = early trials only. The rating is about the quality of the studies, not about how useful the supplement is.

L-theanine

An amino acid found in green tea, studied mainly in combination with caffeine: alertness without the jitters.

CognitionStressSleep

Benefits

  • Combined with caffeine, improves alertness and attentional accuracy in the two hours that follow (meta-analysis of 11 human trials)
  • Reduces anxiety and depressive symptoms at 200 mg per day over 4 weeks
  • Shortens time to fall asleep and reduces nighttime awakenings
  • Lowers heart rate in stressful situations, and mitigates the rise in blood pressure caused by caffeine

Precautions

Well tolerated at the doses studied. Caution in case of treatment for hypertension, as theanine may slightly lower blood pressure.

Interacts with:Antihypertensives

Recommended dosage

200 mg per day; 200 to 250 mg in a single dose, often with caffeine, in trials on focus.

How to take it

  • Dose: 200 mg per day in the four-week trial on stress and sleep; 200 to 250 mg in a single dose in trials on focus.
  • With caffeine: the combination improves alertness and attention, especially in the two hours following intake.
  • How long: a single dose has already reduced the heart's reaction to a stressful task. On sleep and anxiety, the trial lasted four weeks.

What the studies say

  • This systematic review and meta-analysis, based on 11 placebo-controlled human studies, evaluated the acute effects of L-theanine, alone or in combination with caffeine, on cognitive function and mood. Evidence of moderate effects was found in favor of the combination of caffeine and L-theanine on alertness, attentional switching accuracy, and certain attentional outcomes, particularly in the first two hours post-dose.

    Camfield DA, Stough C, Farrimond J, Scholey AB. — Nutrition reviews (2014) — View the source study

For information only: not a substitute for medical advice. Dietary supplements are not a replacement for a varied, balanced diet. Learn more