Amino acid found in tea · Fact sheet
L-theanine
Also known as Theanine
L-theanine has small human studies of stress, attention, and sleep. Some findings are favorable, but placebo responses and mixed results mean it is not an established treatment for anxiety or insomnia.
What is L-theanine?
L-theanine is an amino acid found in tea. Studies of isolated L-theanine cannot be treated as identical to tea or combinations containing caffeine.
Benefits people look for
Feeling calm without sedation, concentrating more easily, and sleeping better are common expectations. Subjective calm and improved performance are different endpoints.
What the evidence supports
- One small crossover trial found improvements in selected sleep-quality subscales.
- Other findings were mixed; improvements from baseline alone do not prove superiority to placebo.
All research areas
- Perceived stress
- Attention tasks
- Sleep quality
Anecdotal reports & lived experiences
Reports describe what someone noticed. They cannot establish cause, typical results, or how often a side effect happens.
A calmer subjective response to stress
A recent personal account described a marked sense of calm after starting L-theanine and asked whether that experience could persist long term.
The short account has no comparison group, validated anxiety assessment or long-term follow-up. It does not establish equivalence to a medical treatment.
Read the calming-experience report ↗A racing-heart report whose attribution later changed
One person initially blamed L-theanine for waking with a racing heart after previously finding it helpful for sleep, but later updated the post to suggest valerian instead.
Multiple supplements, travel, a changed product and irregular sleep complicate attribution. The correction is essential: this is not a confirmed L-theanine reaction.
Read the account and its correction ↗Side effects & risks
- These small trials cannot establish uncommon adverse effects, long-term safety, or safety of combinations.
- The 28-day study found less total time asleep, so it should not be summarized as uniformly improving sleep.
This is a summary of the cited evidence, not a complete product label. A lack of human safety data does not establish safety.
Clinical research: how strong is it?
Early human evidenceTwo 30-person trials offer short-term signals. In the 28-day study, perceived stress improved similarly in both groups and cortisol changes did not differ significantly, despite some positive attention findings.
Selected research to read
30-person crossover trial in adults without major psychiatric illness.
30-person randomized study with mixed between-group findings.
Registered stress, sleep, attention, and safety endpoints for the 28-day study.
FDA approval & research status
L-theanine has no FDA-approved drug indication for the wellness uses discussed here. Supplement availability is not premarket FDA approval of effectiveness or safety.
No FDA-approved use is documented in the records summarized on this page.
Supplement research is not FDA drug approval
L-theanine has no FDA-approved drug indication for the wellness uses discussed here. Supplement availability is not premarket FDA approval of effectiveness or safety.
This summarizes the cited product or research record. Trial phases do not establish successful completion of earlier stages, and a stopped program is not ongoing development. Approval applies only to the labeled product, use and population.
What we still don’t know
- Clinically meaningful benefits in diagnosed anxiety or insomnia
- Long-term effects and medication interactions
- Reproducibility outside small, product-specific trials
The takeaway
Other findings were mixed; improvements from baseline alone do not prove superiority to placebo.
Sources & further reading
Medical evidence and regulatory sources are listed here. Personal reports are linked separately in the experiences section.
- 1pubmedL-theanine and stress-related symptoms
30-person crossover trial in adults without major psychiatric illness.
- 2pubmed28-day L-theanine trial in moderately stressed adults
30-person randomized study with mixed between-group findings.
- 3clinical trialsL-theanine randomized-trial registry
Registered stress, sleep, attention, and safety endpoints for the 28-day study.
- 4fdaFDA: what approval means for supplements
Dietary supplements are not approved by FDA for safety and effectiveness before marketing.