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L-theanine

Amino acid from green tea leaves (Camellia sinensis), supplement

ATC code: A16AA-L-THEANINE

Brand names: Now L-Theanine, Solgar L-Theanine, Suntheanine, Natrol L-Theanine

Updated · Methodology

Marketing claims without evidence base

The drug is promoted for these uses outside international guidelines. Each entry below is analyzed against AEMPS, FDA, EMA, Cochrane and major RCTs.

D

Hypertension

Not recommended

L-theanine is an amino acid found in tea. Evidence that it lowers blood pressure is lacking. In one trial it only blunted a short-lived rise in blood pressure during mental stress, and only in people with an exaggerated stress response, without lowering resting blood pressure. A separate randomized trial found no difference from placebo. has not approved any health claim for L-theanine, including the stress-relief effect that marketers use to explain a blood-pressure benefit.

Sources

  1. Journal of Physiological Anthropology: Effects of L-theanine or caffeine intake on changes in blood pressure under physical and psychological stresses (2012)
  2. Foods: The Effect of L-Theanine Incorporated in a Functional Food Product (Mango Sorbet) on Physiological Responses in Healthy Males: A Pilot Randomised Controlled Trial (2020)
  3. EFSA Journal: Scientific Opinion on the substantiation of health claims related to L-theanine from Camellia sinensis (L.) Kuntze (tea) and improvement of cognitive function, alleviation of psychological stress, maintenance of normal sleep and reduction of menstrua (2011)

ICD-10: I10 · ICD-11: BA00

D

Insomnia and sleep disorders

Not recommended

L-theanine is marketed as a «natural sleep aid» in sleep formulas with melatonin, magnesium and valerian. Small RCTs in healthy students with pre-exam anxiety reported improved subjective sleep quality; no data in chronic insomnia. 2021 and SES 2016 choose CBT-I as first-line for chronic insomnia; L-theanine is in no international sleep guideline. If L-theanine was recommended for chronic insomnia instead of CBT-I or workup for sleep apnoea and restless legs syndrome, consider seeking a second opinion.

Sources

  1. AASM: Behavioral and psychological treatments for chronic insomnia disorder in adults (2021)
  2. SES: Guía de práctica clínica para el manejo del insomnio (2016)
  3. Sleep Medicine Reviews: The effects of L-theanine consumption on sleep outcomes: a systematic review and meta-analysis (2025)

ICD-10: G47.0 · ICD-11: 7A00

D

Memory and concentration enhancement

Not recommended

L-theanine with caffeine is marketed as a «focus stack» (Mind Lab Pro, Alpha Brain and analogues) promising «better focus without jitter». Several small RCTs showed modest improvement in reaction time and attention accuracy with L-theanine 100–200 mg + caffeine 50–100 mg versus caffeine alone in healthy volunteers. The effect is short-lived and comparable to one cup of green tea (about 25–50 mg L-theanine and 30 mg caffeine). 2011 approved no cognitive claim for L-theanine. No data in ADHD, Alzheimer or vascular dementia. If L-theanine was recommended as a stimulant substitute for ADHD, consider seeking a second opinion.

Sources

  1. EFSA: Scientific Opinion on the substantiation of health claims related to L-theanine (no claim approved) (2011)
  2. Nutrients: Effects of L-theanine on stress-related symptoms in healthy adults: a randomised controlled trial (2019)
D

Stress and anxiety

Not recommended

L-theanine is the main marketing claim from supplement makers: promises to «relieve stress», «remove anxiety» and «relax without drowsiness». A single RCT (Hidese 2019, Nutrients, 30 people) found reduced STAI anxiety under acute stress in healthy adults. The Williams 2020 systematic review confirms only a short-term effect under situational stress, with no data on chronic anxiety or clinical anxiety disorders. 2011 did not approve a health claim. CG113 lists SSRIs and CBT first-line for anxiety disorders; L-theanine is not mentioned. If L-theanine was recommended for panic attacks, GAD or social phobia instead of psychotherapy referral, consider seeking a second opinion.

Sources

  1. EFSA: Scientific Opinion on the substantiation of health claims related to L-theanine (no claim approved) (2011)
  2. Nutrients: Effects of L-theanine on stress-related symptoms in healthy adults: a randomised controlled trial (2019)
  3. NICE: Depression in adults: treatment and management (NG222) (2022)
  4. Plant Foods for Human Nutrition: The Effects of Green Tea Amino Acid L-Theanine Consumption on the Ability to Manage Stress and Anxiety (2020)

ICD-10: F41.9 · ICD-11: 6B0Z

How to read tiers A–F
  • AStrong evidence – first or second line in international guidelines
  • BRecommended in selected cases
  • CStudy data contradict each other
  • DBenefit not proven, no documented harm
  • FDocumented harm, or risk without benefit

Mechanism of action

L-theanine is a non-protein amino acid, structurally analogous to glutamate and glutamine. It crosses the blood-brain barrier and raises GABA, serotonin and dopamine levels in animal models. On human EEG it increases alpha-wave activity 30–40 minutes after a 200 mg oral dose, interpreted as «relaxed alertness». No known human receptors; weak NMDA antagonism and glutamate modulation are discussed. Metabolised in the liver to ethylamine and glutamate, excreted in urine. Half-life 1–3 hours. 2011 did not approve any health claim for L-theanine.

Safety

Contraindications

  • Pregnancy and lactation (precautionary principle)
  • Children under 18 years (no safety data)
  • Antihypertensive therapy (theoretical additive hypotensive effect)

Serious adverse effects

  • Allergic reactions (rare)
  • Masking of anxiety and depressive disorder symptoms, delaying psychiatric referral

Common adverse effects

  • Headache
  • Nausea
  • Mild blood pressure reduction

Pregnancy: can you take L-theanine?

No RCT data in pregnancy. Supplement manufacturers state «do not use during pregnancy» on labels. AEMPS does not register L-theanine as a medicine; no ficha técnica. Green tea as a beverage in moderate amounts is allowed; concentrated extract is not.

Breastfeeding: can you take L-theanine?

No data on milk transfer. LactMed has no monograph for L-theanine as a monoproduct. Lactating women should avoid concentrated extracts and limit intake to green tea as a beverage (up to 200 mg caffeine per day).

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Reference information, not a clinical decision. Discuss feeding pauses or changes with your physician or an IBCLC.

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Frequently asked

What is L-theanine used for?

L-theanine is evaluated for the following indications with varying evidence strength: Insomnia and sleep disorders (evidence tier D), Hypertension (evidence tier D), Stress and anxiety (evidence tier D). See the full indication matrix with dosing and citations above on this page.

What are the side effects of L-theanine?

Common side effects of L-theanine (≥ 1 in 100): Headache, Nausea, Mild blood pressure reduction. See the Safety section for uncommon and serious reactions.

Is L-theanine safe during pregnancy?

No RCT data in pregnancy. Supplement manufacturers state «do not use during pregnancy» on labels. AEMPS does not register L-theanine as a medicine; no ficha técnica. Green tea as a beverage in moderate amounts is allowed; concentrated extract is not.

Is L-theanine compatible with breastfeeding?

No data on milk transfer. LactMed has no monograph for L-theanine as a monoproduct. Lactating women should avoid concentrated extracts and limit intake to green tea as a beverage (up to 200 mg caffeine per day).

Who should not take L-theanine?

L-theanine is contraindicated in: Pregnancy and lactation (precautionary principle); Children under 18 years (no safety data); Antihypertensive therapy (theoretical additive hypotensive effect). Full list in the Safety section.

Other drugs in this group

L-tyrosine, Licorice root (Glycyrrhiza glabra, root and rhizome; including deglycyrrhizinated DGL), Lion's Mane Mushroom (Hericium erinaceus), Medium-chain triglycerides (MCT, coconut oil C8–C10), N-acetyl-L-tyrosine, Astragalus root (Astragalus membranaceus; Huang Qi in traditional Chinese medicine), D-aspartic acid (DAA), Levocarnitine (L-carnitine)