L-theanine
An amino acid from tea. It may help sleep quality a little, without sedation. It has no proven effect on ADHD symptoms.
At a glance
| Our verdict | May help sleep quality a little where a busy mind is the problem; safe. Not for ADHD symptoms. |
| Best use | Sleep quality; a busy mind |
| How sure the evidence is | Low for sleep; Very low for ADHD |
| Cost a month | About $10 to $20 (estimated) |
Written for adults in Canada. It explains the evidence; it is not advice for you personally. Last reviewed 20 October 2026.
Supplement Check
Is it right for you?
Poor sleep has many causes, and some, like sleep apnoea, need a doctor rather than a supplement. Your check screens for them first and tells you whether L-theanine is worth trying. Our Supplement Check looks at:
- Possible sleep apnoea (loud snoring, stopping breathing, daytime sleepiness)
- Pregnancy and breastfeeding (no data)
- The combination with caffeine
- Every medicine you take
Coming soon. The Supplement Check and the Online Health Assessment open once our safety testing is complete.
$59 when it opens, paid once. Adults 18 and over, anywhere in Canada. While the service is new, Dr. French reads every report himself, and your report arrives within 3 working days. More about the Supplement Check
What it is
L-theanine is an amino acid found in tea (Camellia sinensis). Suntheanine is the ingredient used in the trials. It is licensed in Canada under a Health Canada monograph (January 2026).
How it acts
It acts on glutamate receptors and has modest effects on GABA, a calming nerve messenger, and it increases alpha waves on a brain-wave recording. It also blunts the arousal and blood-pressure rise from caffeine. That is mechanism; the trial results are below.
What it is used for, and what the evidence says
| Use | What the trials found | How sure we are |
|---|---|---|
| Sleep quality, adults | 19 trials, 897 people: sleep quality improved by a small to moderate amount on questionnaires (effect size 0.43), and daytime functioning a little (0.33). [1] No sedation. | Low |
| Sleep in boys with ADHD | 98 boys took 400 mg a day for 6 weeks: time asleep and sleep efficiency measured with a wrist monitor improved; time to fall asleep did not change, and parents did not notice a difference. [2] | Low |
| Attention and stress, healthy adults | 31 trials, 1,168 people: a single 200 mg dose made reaction-time tests faster (effect size 0.51) and reduced short-term stress a little (0.31, trials at high risk of bias); no effect on fatigue. [3] These are laboratory tests, not ADHD symptoms. | Not graded (laboratory tests) |
| ADHD symptoms, adults | No trial of L-theanine on ADHD symptoms in adults. | No evidence (no trial) |
| With caffeine, children with ADHD | One crossover trial in 5 boys: L-theanine with caffeine improved an attention test and a stop-signal test; caffeine alone made self-control on the test worse. [4] No symptom questionnaire was used. | Very low |
How sure we are: High means further research is very unlikely to change the answer; Moderate, it might; Low, it may well change; Very low, we are very unsure. These follow the GRADE method that guideline panels use.
Benefits
- A small improvement in self-rated sleep quality, without sedation. [1]
- Better measured sleep efficiency in one trial in boys with ADHD. [2]
- No proven effect on ADHD symptoms.
Risks and side effects
- Well tolerated up to 400 mg a day.
- Headache, mild stomach upset, drowsiness.
Interactions with medicines
Our review found no report that it speeds up or blocks the liver enzymes that clear medicines; that question has not been studied for it.
| Medicine | What can happen | What to do |
|---|---|---|
| Blood-pressure medicines | May lower blood pressure slightly more | Fine; tell your doctor you take it |
| Caffeine | Blunts caffeine's arousal (intended in combination products) | Fine |
| ADHD stimulants and atomoxetine | Not tested together; a caffeine-containing product adds to the stimulant's effect on blood pressure and pulse | L-theanine alone at night: check blood pressure and pulse within 2 weeks; no caffeine combination |
| MAOI antidepressants and related medicines, now or in the last 14 days: phenelzine, tranylcypromine, moclobemide, selegiline, rasagiline, safinamide, linezolid, methylene blue | The caffeine in combination products is the concern | No caffeine combination |
Who should not take it
- Possible sleep apnoea (loud snoring, stopping breathing, daytime sleepiness): checked first, before any sleep product. Dr. French's rule.
- Pregnancy and breastfeeding (no data).
- The combination with caffeine: not for anyone on a stimulant, with a heart rhythm problem, uncontrolled blood pressure, an anxiety disorder, insomnia, or on an MAOI. It is held for Dr. French and never given automatically.
- Under 18: outside the Supplement Check.
Dose and timing
- 200 mg in the evening. Up to 400 mg at night was used in the ADHD sleep trial. [2]
- Keep a sleep diary, or use a wearable's sleep score, for 2 to 6 weeks. If sleep quality does not change, stop.
- A sleep programme works better: use L-theanine alongside it, not instead of it.
What we know about Canadians
About 1 in 6 Canadian adults (16.3%) had insomnia disorder in a 2023 national survey. [5] Night-time insomnia symptoms affect 18 to 20% of adults and 24% of women aged 18 to 64. [6] People reach for help on their own: in one year, 28.7% used natural products or over-the-counter sleep aids, 15.6% cannabis, 14.7% prescribed sleeping pills and 9.7% alcohol. [5]
Sleep apnoea often hides behind poor sleep: among Canadians aged 45 to 85, 28.1% were at high risk of moderate to severe sleep apnoea, and only 1.2% had been diagnosed. [7]
Most at risk of insomnia: women, Indigenous people (1.8 times), people in poorer mental or physical health, older adults and young adults.
How sure are we: moderate. Population survey with standard criteria, but self-reported (2023 national sample of 4,037 adults).
An honest comparison: sleep
Cost a month in Canadian dollars. The L-theanine trials measured sleep-quality questionnaires rather than minutes, so its row is not in the same units as the others.
| Option | Effect | How sure we are | Cost a month (CAD) |
|---|---|---|---|
| Magnesium bisglycinate 200 to 400 mg | About 17 minutes faster to sleep in older adults [10] | Low to Very low | $12 to $20 |
| L-theanine 200 mg | Sleep quality effect size 0.43, 19 trials [1] | Low | $15 to $20 |
| Cognitive behavioural therapy for insomnia (app, programme or therapist) | 19 minutes faster to sleep, 26 minutes less awake in the night, sleep efficiency up 9.9%; lasts after treatment ends [8] | Moderate to High | Free (app) to about $90 (therapist) |
| Regular exercise | Small benefit on total sleep, moderate on sleep quality [9] | Moderate | $0 to $21 |
| Sleeping pill (zopiclone in Canada) | 22 minutes faster to sleep on sleep studies; the benefit stops when the pill stops [11] | Moderate | $8 to $12 |
Read honestly: a sleep programme does far more than L-theanine and keeps working after it ends. L-theanine is cheap and safe, so it is a reasonable add-on where a busy mind keeps you awake.
Our verdict
A personal choice for adults whose sleep is poor because a busy mind keeps them awake, once sleep apnoea has been checked: 200 mg in the evening, alongside a sleep programme, for a few weeks with a sleep diary. The benefit is small and the evidence is of low certainty.
Not for ADHD symptoms: it has no proven effect on them. For adults with diagnosed ADHD who are not on a stimulant, L-theanine with caffeine in the morning is an option Dr. French considers in person; our check never offers it automatically. If a questionnaire suggests ADHD, that is a screen, not a diagnosis: it needs a formal assessment. If ADHD is confirmed, the prescription medicines reduce symptoms two to four times more than any supplement.
Across 19 trials L-theanine improved sleep quality a little, [1] it does not sedate, it is well tolerated up to 400 mg a day, and it costs $10 to $20 a month. A sleep programme does far more, so L-theanine is an add-on, not a treatment. In ADHD the only trials are small and in boys, and they measured sleep or laboratory tests, not symptoms; [2, 4] so we offer it for sleep only, and say so.
Supplement Check
Before you buy it, get it checked
Poor sleep has many causes, and some, like sleep apnoea, need a doctor rather than a supplement. Your check screens for them first and tells you whether L-theanine is worth trying. Our Supplement Check looks at:
- Possible sleep apnoea (loud snoring, stopping breathing, daytime sleepiness)
- Pregnancy and breastfeeding (no data)
- The combination with caffeine
- Every medicine you take
Coming soon. The Supplement Check and the Online Health Assessment open once our safety testing is complete.
$59 when it opens, paid once. Adults 18 and over, anywhere in Canada. While the service is new, Dr. French reads every report himself, and your report arrives within 3 working days. More about the Supplement Check
Disclosure of financial interest
White Pine Medical earns money from products bought through our Fullscript dispensary. Dr. French's Code of Ethics requires him to tell you this. You do not have to buy anything from us: every product is named by its ingredient and dose so you can buy it at any pharmacy, and the advice is the same wherever you buy it, or if you buy nothing.
References
- Bulman A, D'Cunha NM, Marx W, et al. The effects of L-theanine consumption on sleep outcomes: a systematic review and meta-analysis. Sleep Med Rev. 2025;81:102076.
- Lyon MR, Kapoor MP, Juneja LR. The effects of L-theanine (Suntheanine) on objective sleep quality in boys with attention deficit hyperactivity disorder (ADHD): a randomized, double-blind, placebo-controlled clinical trial. Altern Med Rev. 2011;16(4):348-54. PMID 22214254.
- Gerolymos C, Saddier E, Boyer L, Fond G. Cognitive and affective effects of L-theanine: a systematic review and meta-analysis of 31 randomized trials. Mol Psychiatry. 2026;31(11):6592-602. PMID 42410082.
- Kahathuduwa CN, Wakefield S, West BD, et al. Effects of L-theanine-caffeine combination on sustained attention and inhibitory control among children with ADHD: a proof-of-concept neuroimaging RCT. Sci Rep. 2020;10(1):13072. PMID 32753637.
- Morin CM, Vézina-Im LA, Chen SJ, Ivers H, Carney CE, Chaput JP, et al. Prevalence of insomnia and use of sleep aids among adults in Canada. Sleep Med. 2024;124:338-45. PMID 39369578.
- Chaput JP, Morin CM, Robillard R, Carney CE, Dang-Vu TT, Davidson JR, et al. Trends in nighttime insomnia symptoms in Canada from 2007 to 2021. Sleep Med. 2025;125:21-6. PMID 39556998.
- Rizzo D, Baltzan M, Sirpal S, Dosman J, Kaminska M, Chung F. Prevalence and regional distribution of obstructive sleep apnea in Canada: analysis from the Canadian Longitudinal Study on Aging. Can J Public Health. 2024;115(6):970-9. PMID 39037568.
- Trauer JM, Qian MY, Doyle JS, Rajaratnam SM, Cunnington D. Cognitive behavioral therapy for chronic insomnia: a systematic review and meta-analysis. Ann Intern Med. 2015;163(3):191-204. PMID 26054060.
- Kredlow MA, Capozzoli MC, Hearon BA, Calkins AW, Otto MW. The effects of physical activity on sleep: a meta-analytic review. J Behav Med. 2015;38(3):427-49.
- Mah J, Pitre T. Oral magnesium supplementation for insomnia in older adults: a systematic review and meta-analysis. BMC Complement Med Ther. 2021;21(1):125. PMID 33865376.
- Huedo-Medina TB, Kirsch I, Middlemass J, Klonizakis M, Siriwardena AN. Effectiveness of non-benzodiazepine hypnotics in treatment of adult insomnia: meta-analysis of data submitted to the Food and Drug Administration. BMJ. 2012;345:e8343. PMID 23248080.
Costs marked as estimates are typical Canadian retail or pharmacy prices, before any drug plan. Certainty grades are ours unless the review gave its own.