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L-Theanine: What It Is, Evidence and Safety

VITAMINS & SUPPLEMENTS · COMPARED

L-Theanine vs Ashwagandha for Calm and Stress: What Research Compares

L-theanine is an amino acid from tea and ashwagandha is a herb. What reviews found for stress, anxiety and sleep, how they differ on safety, and why no trial compares them directly.

Content last updated . This page has not been medically reviewed.

Back to L-Theanine: What It Is, Evidence and Safety

The question

L-theanine and ashwagandha are both sold for calm and stress. They are very different products: one is a single amino acid, the other a whole-plant extract. This page compares what research has found for each, for stress, anxiety and sleep, and where their safety questions differ. Goal-level advice on stress lives in Stress and relaxation; this page stays at ingredient level.

What each one is

  • L-theanine is described as "the green tea amino acid" and has been reviewed as a stand-alone supplement. [1] Full profile: L-theanine.
  • Ashwagandha (Withania somnifera) is an evergreen shrub used for thousands of years in Ayurvedic medicine; supplements typically contain root, leaf or root/leaf extracts, and trials used a variety of preparations. [2] See Adaptogens and Ashwagandha in Ayurveda.

What the research found

7 findings · 2 supported · 2 mixed · 3 limited or unclearThe colour follows the evidence label on each card.

  1. Ashwagandha for stress

    Promising but limited

    A 2022 meta-analysis of 12 trials (1,002 adults aged 25 to 48) found lower stress scores than placebo; the authors rated certainty low and results varied widely between trials. [3] NCCIH says some preparations may be effective for stress and insomnia, but evidence on anxiety is unclear. [2]

  2. Ashwagandha for sleep

    Promising but limited

    Five trials (400 people): a small but significant improvement in overall sleep, larger in people with insomnia. [4]

  3. L-theanine for stress

    Mixed

    A 2026 meta-analysis of 31 trials (1,168 people): a single dose gave a modest reduction in acute stress, largely influenced by studies with a high risk of bias. [5]

  4. L-theanine for anxiety

    Mixed

    The same 2026 analysis found anxiety effects inconsistent and non-significant apart from one study. [5] A 2020 review of 9 trials said 200 to 400 mg a day (study amounts) may assist people exposed to stressful conditions, and called for larger, longer studies. [1]

  5. L-theanine for sleep

    Insufficient evidence (one small trial)

    A 4-week crossover trial of 30 adults found sleep-quality scores improved on 200 mg a day (study amount). [6] The L-theanine and placebo tablets were supplied by a company that employs two of the authors. [6]

  6. Both in one analysis

    Indirect only

    A 2022 network meta-analysis of herbs for anxiety found Withania somnifera lowered Hamilton Anxiety scores, with small trials, while L-theanine did not outperform placebo with statistical certainty; the authors called results preliminary. [7]

  7. Ashwagandha vs L-theanine head to head

    None

    Proper evidence not found. We searched PubMed for trials and reviews that compared the two directly; none turned up.

Study amounts above describe what was tested, not what a person should take. Anxiety disorders and long-lasting low mood need a clinician.

No universal winner

Ashwagandha has more trials for stress and sleep but more safety cautions. L-theanine had no serious adverse events reported in the trials reviewed but has modest and inconsistent results for stress. Neither has been tested against the other. A clinician or pharmacist can say which fits your health and medicines.

Frequently asked questions

Is L-theanine or ashwagandha better for stress?

Proper evidence not found for a direct comparison. Each has trials against placebo with mixed to promising, low-certainty results. [3][5]

Is ashwagandha safe?

NCCIH says it may be safe short term (up to 3 months), but liver injury has been linked to it and it should be avoided in pregnancy. [2]

Does L-theanine have side effects?

A 2026 meta-analysis of 31 trials reported no serious adverse events. [5] Long-term safety is not described in the sources we read.

Can I use both together?

No trial in the sources we read tested the combination, so we cannot describe its effects. Ask a pharmacist, especially if you take sedating or other regular medicines.

Do these treat anxiety?

No source we read shows that either treats an anxiety disorder; NCCIH says ashwagandha's effects on anxiety are unclear. [2]

More details: evidence, limits and cautions

The details behind this page: cautions, limits of the evidence and where sources disagree. Open any note to read it.

How to read the evidence labels

Labels used on this page: promising but limited, mixed, insufficient evidence, Proper evidence not found.

Safety: where they differ
AshwagandhaL-theanine
LiverNCCIH says liver injury is rare but has been linked to ashwagandha supplements. [2] A case series of five people described jaundice 2 to 12 weeks after starting, with liver tests normalizing in 1 to 5 months in four. [8]The 2026 meta-analysis reported no serious adverse events. [5]
Pregnancy and breastfeedingNCCIH says avoid during pregnancy and do not use while breastfeeding. [2]Not described in the sources we read.
Thyroid, autoimmune, surgeryNCCIH says not recommended before surgery or for people with autoimmune or thyroid disorders. [2]Not described in the sources we read.
MedicinesNCCIH says ashwagandha might interact with diabetes, blood pressure, immune-suppressing, sedative, anti-seizure and thyroid medicines. [2]Not described in the sources we read.
DurationPossibly safe up to 3 months; long-term safety unknown. [2]Long-term safety: not described in the sources we read.

Not described does not mean safe. Read How interactions work, Liver safety and supplements and Quality testing and certifications. Children and older adults: neither product was reviewed for these groups in the sources we read, so ask a clinician or pharmacist. Yellow skin or eyes, dark urine or severe tiredness while using any supplement should be checked by a clinician promptly.

For wider comparisons see Calming supplements compared and Supplements, teas and adaptogens for stress compared.

References
  1. Williams JL et al. The effects of green tea amino acid L-theanine consumption on the ability to manage stress and anxiety levels: a systematic review. Plant Foods Hum Nutr. 2020. Read 2026-10-23.
  2. National Center for Complementary and Integrative Health (US). Ashwagandha: Usefulness and Safety. Last updated March 2023. Read 2026-10-23.
  3. Akhgarjand C et al. Does ashwagandha supplementation have a beneficial effect on the management of anxiety and stress? A systematic review and meta-analysis of randomized controlled trials. Phytother Res. 2022. Read 2026-10-23.
  4. Cheah KL et al. Effect of ashwagandha (Withania somnifera) extract on sleep: a systematic review and meta-analysis. PLoS One. 2021. Read 2026-10-23.
  5. Gerolymos C et al. Cognitive and affective effects of L-theanine: a systematic review and meta-analysis of 31 randomized trials. Mol Psychiatry. 2026. Read 2026-10-23.
  6. Hidese S et al. Effects of L-theanine administration on stress-related symptoms and cognitive functions in healthy adults: a randomized controlled trial. Nutrients. 2019. Read 2026-10-23.
  7. Zhang W et al. Medicinal herbs for the treatment of anxiety: a systematic review and network meta-analysis. Pharmacol Res. 2022. Read 2026-10-23.
  8. Björnsson HK et al. Ashwagandha-induced liver injury: a case series from Iceland and the US Drug-Induced Liver Injury Network. Liver Int. 2020. Read 2026-10-23.
Education, not medical advice. This page is for general information. It does not diagnose or treat any condition and is not a substitute for care from a qualified health professional. Natural does not automatically mean safe. Ask a clinician or pharmacist before changing your care, especially if you take medication, are pregnant or breastfeeding, or have a health condition.