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Awaiting clinical review. This entry is sourced but has not yet been signed off by a pharmacist or clinician.

Amino acid from tea (Camellia sinensis)

L-Theanine

L-theanine has a small, fairly consistent effect on attention in healthy adults: a single 200 mg dose improved choice reaction time in a 2026 meta-analysis of 31 trials. Its effects on stress, anxiety and sleep are smaller and less certain, and none of the trials were long enough to say much about long-term safety. It was well tolerated in the trials reviewed, but we found no source on use in pregnancy, so that remains unknown.

Updated
29 September 2026
White capsules beside a cup of green tea
At a glance
Last reviewed 29 September 2026
Evidence
Moderate
Best for
Attention and reaction time
Typical form & use
Capsule or tablet, 200 mg
Onset
Same night
Safety
Pregnancy and long-term safety data are lacking. No interactions in our data.
Check with your medications →

What it's used for

Evidence is rated per use. The same ingredient can be strong for one thing and traditional for another.

UseEvidenceWhat the research shows
Attention and reaction timeModerateA meta-analysis of 31 randomised trials (1,168 people) found a single 200 mg dose taken 30–60 minutes before testing improved choice reaction time (SMD 0.51, 95% CI 0.25–0.77). A separate meta-analysis of five trials in 148 healthy adults found a 15 ms faster response on one task but no significant effect on simple reaction time or the Stroop test, so the benefit is not seen on every measure. Effects on wider cognition are unproven.1,2
Caffeine plus L-theanineLimitedA meta-analysis of 50 trials of tea, theanine, or theanine with caffeine found small-to-moderate differences from placebo favouring theanine plus caffeine on some attention and mood measures in the first two hours, but the confidence intervals often crossed zero (for example choice reaction time at one hour, SMD -0.48, 95% CI -1.01 to 0.05). The authors say the direction and size of the effect remain uncertain. This review was partly funded by tea companies. We did not find, and cannot say from these sources, whether the combination beats caffeine alone.3
Sleep qualityLimitedA meta-analysis of 18 randomised trials (897 people) found small improvements in subjective sleep onset latency (SMD 0.15, 95% CI 0.01–0.29), daytime dysfunction and overall sleep-quality scores. Its authors note few trials used pure L-theanine. A systematic review of 13 trials reported benefit at 200–450 mg a day, but most of the outcomes were self-reported and clinical insomnia has barely been tested.4,5
Stress and anxietyLimitedIn the 31-trial meta-analysis the reduction in acute stress was modest (SMD 0.31) and largely driven by trials at high risk of bias, and anxiety effects were inconsistent and non-significant apart from one trial in psychotic anxiety. One small crossover trial of 30 healthy adults found lower trait-anxiety scores after four weeks on 200 mg a day, and a systematic review of 11 trials in people with psychiatric diagnoses reported symptom reductions in anxiety disorders, mostly as an add-on to other treatment. These are small and short studies, and several used supplier-provided product.1,6,7

How much

Ranges below are what studies used and what supplements commonly contain. They are not a recommendation for you. Start at the low end.

Attention (single dose)
200 mg1
The dose behind the reaction-time result in the 31-trial meta-analysis, taken 30–60 minutes before testing.
Daily use studied
200–450 mg a day5,6
The range a 2026 systematic review linked to better sleep. Included trials spanned 50–900 mg a day. One trial of stress-related symptoms gave 200 mg a day for four weeks.
Longest studied
About 8 weeks1
The 8-week, 400 mg a day trial noted in the 31-trial meta-analysis is the longest we saw. We found no source that sets an upper limit or reports safety beyond that.
Timing · For attention, the trials dosed 30–60 minutes before testing. No source we read gave a preferred time of day for stress or sleep.With food? · No source we read gave guidance on food.How long to trial · Attention effects were measured within hours of a single dose. Stress and sleep trials ran about four weeks, so that is a reasonable window to judge those uses.

How people take it

Capsule or tablet200 mgThe form used in the single-dose and four-week trials. Products vary, so check the label for actual L-theanine per serving.
Combined with caffeineVaries by trialStudied as theanine plus caffeine in a single serving. Trial doses differ, so we do not give a standard ratio.
TeaVaries widelyTea contains L-theanine, but the reviewed trials mostly used supplements and the authors call for more work at tea-equivalent doses.

Safety

Who should avoid
  • Pregnancy and breastfeeding — we found no safety data
  • Children — we did not review paediatric data
  • If you take psychiatric medication — ask your prescriber before adding it
Known interactions
No interactions in our data. Absence of a flag is not clearance.

Compare with

Head-to-head pages for the pairs people search most.

L-Theanine vs Ashwagandha

Questions people ask

Does L-theanine help with anxiety?

The evidence is weak. A 2026 meta-analysis found only a modest short-term effect on stress, largely from trials at high risk of bias, and anxiety results were inconsistent. Some small trials show benefit, but they are not enough to call it an anxiety treatment.

Does L-theanine and caffeine work better together?

Some trials found small gains in attention and mood after the two together compared with placebo, but the confidence intervals often included no effect, and the review was partly tea-industry funded. The sources we read do not show it beats caffeine alone.

Will L-theanine make me sleepy?

In the trials it was studied as a daytime attention aid, with faster reaction times, which does not fit a sedative. Sleep trials show small improvements in reported sleep quality, so it should be judged over weeks, not by drowsiness.

Is L-theanine safe?

The 31-trial meta-analysis reported no serious adverse events. The trials were short, so long-term safety and use in pregnancy are unknown.

Sources

  1. Meta-analysis Gerolymos C, Saddier E, Boyer L, Fond G. Cognitive and affective effects of L-Theanine: a systematic review and meta-analysis of 31 randomized trials. Mol Psychiatry. 2026.
  2. Meta-analysis Mátyus RO, Szikora Z, Bodó D, et al. Promising, but Not Completely Conclusive: The Effect of l-Theanine on Cognitive Performance, a systematic review and meta-analysis of randomized placebo-controlled clinical trials. J Clin Med. 2025.
  3. Meta-analysis Payne ER, Aceves-Martins M, Dubost J, Greyling A, de Roos B. Effects of Tea (Camellia sinensis) or its Bioactive Compounds l-Theanine or l-Theanine plus Caffeine on Cognition, Sleep, and Mood in Healthy Participants. Nutr Rev. 2025.
  4. Meta-analysis Bulman A, D'Cunha NM, Marx W, Turner M, McKune A, Naumovski N. The effects of L-theanine consumption on sleep outcomes: A systematic review and meta-analysis. Sleep Med Rev. 2025.
  5. Systematic review Cotter J, Caddick CE, Harper JL, Ebajemito JK. Examining the effect of L-theanine on sleep: a systematic review of dietary supplementation trials. Nutr Neurosci. 2026.
  6. Randomised trial Hidese S, Ogawa S, Ota M, et al. Effects of L-Theanine Administration on Stress-Related Symptoms and Cognitive Functions in Healthy Adults: A Randomized Controlled Trial. Nutrients. 2019.
  7. Systematic review Moshfeghinia R, Sanaei E, Mostafavi S, et al. The effects of L-theanine supplementation on the outcomes of patients with mental disorders: a systematic review. BMC Psychiatry. 2024.

Last reviewed 29 September 2026 · Next review March 2027 · How we rate evidence