← All supplements

L-theanine

Supplement amino acid brain & moodsleep
Aka: theanine, AlphaWave, Suntheanine
Brands seen in Singapore: California Gold Nutrition, Nutricost, NOW Foods, Doctor's Best, Life Extension
Not medical advice. Check with your doctor or pharmacist before you start, stop or change the timing of anything you take.
How to use
What it’s for
Small cognitive effects · sleep evidence inconclusive
When to take
200 mg at bedtime in the RCT
Take with
Often paired with caffeine · gains mostly come from caffeine
Studied for
The RCT ran four weeks
Pros & cons
Pros
  • Theanine alone: small gains in choice reaction time
  • 200 mg/day, 4 weeks: better psqi sleep scores (n=30)
  • No adverse events in the 4-week 200 mg trial
Cons
  • Small trials; cis often include no effect at all
  • Sleep evidence is inconclusive across trials
  • The key sleep trial was funded by the suntheanine maker
Sources
  1. Effects of Tea (Camellia sinensis) or its Bioactive Compounds l-Theanine or l-Theanine plus Caffeine on Cognition, Sleep, and Mood in Healthy Participants: A Systematic Review and Meta-Analysis of RCTs (Payne et al., Nutr Rev 2025;83(10):1873–1891) — Discussion · read 2026-08-27
    what it says
    “theanine alone may confer small-to-moderate improvements, on cognitive performance measures during the first and second hours after intake … the CIs were frequently consistent with little-to-no difference … The evidence regarding the effects of … theanine alone on sleep outcomes was inconclusive”
  2. Payne et al., Nutr Rev 2025 (same review) — Introduction + Results, choice reaction time · read 2026-08-27
    what it says
    “beneficial effects of tea, or theanine plus caffeine, on cognition and mood, mostly being driven by caffeine … a small-to-moderate difference between the effects of theanine and placebo that favored theanine on choice reaction time”
  3. Effects of L-Theanine Administration on Stress-Related Symptoms and Cognitive Functions in Healthy Adults: A Randomized Controlled Trial (Hidese et al., Nutrients 2019;11(10):2362) — Abstract + Results · read 2026-08-27
    what it says
    “randomized, placebo-controlled, crossover, and double-blind trial … Participants were 30 individuals … L-theanine (200 mg/day) … for four-week administration … Pittsburgh Sleep Quality Index (PSQI) scores decreased after L-theanine administration … adverse events were not apparent during the intervention period”
  4. Hidese et al., Nutrients 2019 (same trial) — Methods + Funding · read 2026-08-27
    what it says
    “Suntheanine, Taiyo Kagaku Co., Ltd … orally self-administered before sleep each night for four weeks … relatively high compared to the median amount of L-theanine per cup of green tea (8–30 mg) … funding received from Taiyo Kagaku Co., Ltd.”
  5. HSA Singapore — Health Supplements Guidelines GL-CHPB-3-001 Rev. No. 020 (January 2026), s4.8 general-adult limits, Tables 4–5 (vitamins and minerals only) · read 2026-08-27
    what it says
    “4.8 HS for use by the general adult population should not contain vitamins and minerals exceeding the stipulated limits stated in Tables 4 and 5”
  6. HSA Singapore — Guidelines on Prohibited and Restricted Ingredients in Health Supplements and Traditional Medicines, GL-CHPB-1-012 Rev. 001 (October 2025), Annex A + Annex B (theanine not listed in either) · read 2026-08-27
    what it says
    “1.3 The objective of this guideline is to highlight the substances of concern when used in HS and TM and is not meant to be an exhaustive list”
  7. iHerb Singapore — L-Theanine category, default order (SGD pricing) · read 2026-08-27
    what it says
    “California Gold Nutrition, L-Theanine, Featuring AlphaWave®, 200 mg, 60 Veggie Capsules … Nutricost, L-Theanine, 200 mg, 120 Capsules … NOW Foods, L-Theanine, 120 Veg Capsules … Doctor's Best, L-Theanine, 150 mg, 90 Veggie Caps … Life Extension, L-Theanine, 60 Vegetarian Capsules”
Report a correction View as JSON

Updated 2026-08-29. Every line above traces to a numbered source. Kozen-X is not a medical device and does not give medical advice. It lists what published sources have written down — nothing more. A pair not listed is unrecorded, not cleared. Before you start, stop or re-time anything, talk to your doctor or pharmacist.