tuneTypical Dose
200-400 mg
Amino Acid
L-Theanine
L-theanine (gamma-glutamylethylamide)
Evidence TierBWADA NOT PROHIBITED
watchEffect Window
Acute calming in 30-90 minutes. Sleep/stress effects typically over 2-8 weeks.
check_circleCompliance
WADA NOT PROHIBITED
Overview
Clinical Summary
L-theanine is a tea-derived amino acid that promotes relaxation without strong sedation. It is used for calmer focus, stress reduction, and sleep quality support, alone or with caffeine.
Trials show reduced stress responses and improved calm-alertness framing, with modest sleep support in some stress-linked settings. Theanine can improve attention and reaction time in selected tasks, especially when combined with caffeine, but monotherapy cognition effects remain domain-specific rather than broad. A newer psychiatric systematic review suggests some adjunctive benefit across mental-disorder settings, yet the evidence is too heterogeneous to treat theanine as a standalone treatment.
Neuromodulatory amino acid that shifts excitatory/inhibitory signaling balance and reduces perceived stress reactivity.
Outcomes
What This Is Expected To Influence
Primary Outcomes
- Stress/anxiety symptom reduction (modest)
- Sleep quality support (modest)
Secondary Outcomes
- Attention quality (stronger with caffeine co-use)
- Stress-reactivity/BP response attenuation in select users
Safety
Contraindications and Interactions
Contraindications
- Symptomatic hypotension (relative)
- Pregnancy (insufficient supplemental safety data)
- Breastfeeding (insufficient supplemental safety data)
Side effects
- Mild headache
- GI discomfort
- Drowsiness/lightheadedness
- Abnormal dreams
Interactions
- Antihypertensive medications (additive BP lowering, monitor for dizziness/hypotension)
- Sedative/CNS depressant medications (additive sedation possible)
- BP-lowering supplements (potential additive hypotension)
- Sedating supplements (potential additive drowsiness)
- Caffeine (changes arousal profile, often smoother stimulation)
Avoid if
- Pregnant
- Breastfeeding
- Frequent orthostatic symptoms without clinician oversight
Evidence
Study-level References
l-theanine-SRC-001Systematic review and meta-analysis.
Sourceopen_in_newMeta-analysis of L-theanine effects on sleep outcomes in adults (PMID: 40056718, 2025).
Population: Adult participants across multiple trial populations.
Dose protocol: Commonly ~200-400 mg/day, variable durations.
Key findings: Modest overall sleep benefit signal.
Notes: Between-study heterogeneity and variable sleep endpoints.
Paper content
Modest overall sleep benefit signal.
l-theanine-SRC-002Systematic review and meta-analysis.
Sourceopen_in_newMeta-analysis of tea/L-theanine effects on cognition, sleep, and mood outcomes (PMID: 40314930, 2025).
Population: Mixed adult cohorts; intervention heterogeneity.
Dose protocol: Theanine alone and tea-derived interventions, acute and chronic.
Key findings: Mixed cognition, modest favorable mood/sleep trends.
Notes: Mixed formulations and co-nutrients (e.g., caffeine, catechins) complicate attribution.
Paper content
Mixed cognition, modest favorable mood/sleep trends.
l-theanine-SRC-003RCT.
Sourceopen_in_newRandomized placebo-controlled trial of chronic L-theanine in stress-related symptoms (PMID: 31623400, 2019).
Population: Adults with stress-related complaints.
Dose protocol: Repeated daily L-theanine over several weeks.
Key findings: Favorable stress/anxiety symptom reduction.
Notes: Moderate sample size, short intervention duration.
Paper content
Favorable stress/anxiety symptom reduction.
l-theanine-SRC-004Randomized crossover trial.
Sourceopen_in_newPlacebo-controlled crossover anti-stress/cognitive trial (PMID: 26797633, 2016).
Population: Healthy adult participants under laboratory stress/cognitive paradigms.
Dose protocol: Acute L-theanine dosing.
Key findings: Favorable calming and selected task benefits.
Notes: Acute lab endpoints may not map directly to daily-life outcomes.
Paper content
Favorable calming and selected task benefits.
l-theanine-SRC-005Controlled human trial.
Sourceopen_in_newL-theanine and stress-related blood pressure response study (PMID: 23107346, 2012).
Population: Stress-reactive adult participants.
Dose protocol: Acute/short-term L-theanine administration.
Key findings: Reduced stress-provoked BP response in higher-stress participants.
Notes: Specific population limits generalizability.
Paper content
Reduced stress-provoked BP response in higher-stress participants.
l-theanine-SRC-006RCT.
Sourceopen_in_new28-day randomized placebo-controlled stress and safety trial of L-theanine (PMID: 38758503, 2024).
Population: Adults with elevated stress burden.
Dose protocol: Daily L-theanine for 28 days.
Key findings: Favorable stress-related symptom pattern with acceptable tolerability.
Notes: Short duration, primarily symptomatic outcomes.
Paper content
Favorable stress-related symptom pattern with acceptable tolerability.
l-theanine-SRC-007Randomized adjunctive clinical trial.
Sourceopen_in_newAdjunctive L-theanine trial in generalized anxiety disorder context (PMID: 30580081, 2019).
Population: Clinical anxiety population receiving standard care.
Dose protocol: Adjunctive oral L-theanine over multi-week period.
Key findings: Supportive but not definitive anxiolytic adjunct signal.
Notes: Adjunctive design limits monotherapy attribution.
Paper content
Supportive but not definitive anxiolytic adjunct signal.
l-theanine-SRC-008Systematic review and meta-analysis of randomized placebo-controlled clinical trials
Sourceopen_in_newMátyus RO, Szikora Z, Bodó D, Vargáné Szabó B, Csupor É, Csupor D, Tóth B. Promising, but Not Completely Conclusive-The Effect of l-Theanine on Cognitive Performance Based on the Systematic Review and Meta-Analysis of Randomized Placebo-Controlled Clinical Trials. J Clin Med. 2025;14(21):7710. doi:10.3390/jcm14217710. PMID:41227106.
Population: Healthy adults enrolled in randomized placebo-controlled l-theanine trials.
Dose protocol: Placebo-controlled l-theanine trials in healthy adults pooled in a 2025 meta-analysis.
Key findings: Meta-analysis found improvement in selected recognition and rapid-processing tasks, but not in every cognitive endpoint studied.
Notes: Best used to narrow the cognition claim rather than strengthen it broadly.
Paper content
The first placebo-controlled l-theanine cognition meta-analysis found possible benefit in selected attention and recognition tasks, but results were inconsistent across tests and limited by the small number of trials.
l-theanine-SRC-009Double-blind, randomized, placebo-controlled trial.
Sourceopen_in_newBaba Y, Inagaki S, Nakagawa S, Kaneko T, Kobayashi M, Takihara T. Effects of l-Theanine on Cognitive Function in Middle-Aged and Older Subjects: A Randomized Placebo-Controlled Study. J Med Food. 2021;24(4):333-341. doi:10.1089/jmf.2020.4803. PMID:33751906.
Population: Japanese men and women aged 50 to 69 years with MMSE-J score of 24 or higher.
Dose protocol: L-theanine versus placebo, single dose and 12-week regular intake, in adults aged 50 to 69.
Key findings: Single dose reduced attention reaction time. Over 12 weeks, improved working memory accuracy, decreased omission errors, and enhanced executive function.
Notes: Direct monotherapy cognitive evidence in an aging population without baseline impairment. Complements the stress and sleep literature.
Paper content
This double-blind RCT tested L-theanine versus placebo in cognitively intact middle-aged and older adults (50 to 69 years). Both single-dose and 12-week regular intake protocols were assessed. A single dose of L-theanine reduced reaction time on attention tasks. Over 12 weeks, L-theanine improved working memory accuracy and reduced omission errors, and enhanced executive function measures. The study provides direct evidence for cognitive benefits of L-theanine monotherapy in an aging population, complementing the stress and sleep literature with a cognitive performance signal in people without baseline impairment.
l-theanine-SRC-010Systematic review of randomized controlled trials
Sourceopen_in_newMoshfeghinia R, Sanaei E, Mostafavi S, Assadian K, Sanaei A, Ayano G, et al. The effects of L-theanine supplementation on the outcomes of patients with mental disorders: a systematic review. BMC Psychiatry. 2024;24:789. doi:10.1186/s12888-024-06285-y. PMID:39633316.
Population: Patients enrolled in randomized L-theanine trials across several mental disorders.
Dose protocol: Systematic review of randomized psychiatric L-theanine trials with variable adjunctive dosing.
Key findings: Review found mixed but potentially favorable adjunctive effects across several mental-disorder settings.
Notes: Important mostly as a boundary-setting source. It supports adjunctive potential while arguing against overconfident psychiatric claims.
Paper content
This systematic review helps keep theanine claims honest. It suggests that L-theanine may be a useful adjunct in some psychiatric settings, but the evidence is heterogeneous across disorders, dosing strategies, and concomitant medications. It supports a cautious adjunctive framing, not a standalone treatment claim.