L-Theanine Ireland: Stress, Focus and Sleep Evidence, Dosage and Stimulant-Free Options
L-theanine is the calm-without-caffeine amino acid from tea. Here is what the human trials actually show for stress, focus and sleep, how it compares with other stimulant-free options, how much to take, and what to buy in Ireland.
What it is. L-theanine is an amino acid from tea leaves, sold in Ireland as a caffeine-free food supplement under FSAI rules. It is not a medicine, and no EU health claim is authorised for it.
What the evidence shows. A 2020 systematic review of 9 studies concluded that 200 to 400 mg a day "may assist in the reduction of stress and anxiety in people exposed to stressful conditions" (Williams et al., Plant Foods Hum Nutr). It did not beat placebo in diagnosed generalised anxiety disorder (Sarris et al., 2019). With caffeine, it improved attention in short-term studies.
What to buy. A single-ingredient 200 mg capsule makes dosing simple. Probiotic.ie stocks NOW Foods L-Theanine 200 mg (120 vegan capsules), shipped from Dublin with no customs charges.
L-theanine definition: L-theanine (γ-glutamylethylamide) is a non-protein amino acid found almost only in the tea plant Camellia sinensis, sold as a caffeine-free supplement, typically in 100 mg or 200 mg capsules.
- What it is: an amino acid from tea leaves
- Contains caffeine? No; supplements are caffeine-free
- Is it a stimulant? No
- Is it a sedative? No; effects are subtle
- Dose in human research: mostly 200 to 400 mg a day
- Often paired with: caffeine, for focus
- EU health claim for L-theanine: none authorised
- Vegan? NOW Foods L-Theanine uses a vegetable capsule
- Irish regulatory status: food supplement under FSAI rules, not a medicine
- Irish VAT on supplements: 13.5%
- L-theanine is not a medicine and is not a treatment for anxiety, insomnia or any condition.
- L-theanine is not a sedative; it does not knock you out.
- L-theanine supplements are not a source of caffeine.
- L-theanine is not proven to lower cortisol on its own.
- L-theanine is not a substitute for your GP if stress or anxiety is affecting daily life.
The short version: if you want something for long, stressful working days that contains no caffeine or other stimulant, the most-researched options are L-theanine (200–400 mg a day), phosphatidylserine (cortisol research at 400 mg a day) and magnesium, which is the only one with authorised EU claims.
What is not proven: that any supplement treats stress, burnout or anxiety. Evidence is from small trials, and EFSA has not authorised stress claims for L-theanine or phosphatidylserine.
Key safety note: if stress is affecting sleep, mood or work, speak to your GP. Check with a pharmacist before combining supplements with prescription medicines.
The research discussed in this article relates to L-theanine as a studied compound. It should not be read as a claim that NOW Foods L-Theanine, or any other product sold by Probiotic.ie, produces these effects. These products are food supplements, not medicines. No authorised EU health claim is made for L-theanine on this page or on any product.
NOW Foods L-Theanine 200 mg Double Strength
200 mg L-theanine with 100 mg inositol per vegan capsule. No caffeine. One capsule once or twice a day. 120 capsules.
Current price on the product page, including Irish VAT at 13.5%. Food supplement, not a medicine. No customs charges. Free DPD delivery on Republic of Ireland orders over €75.
What is L-theanine?
L-theanine is an amino acid found almost only in tea. It is not one of the amino acids your body uses to build protein.
It is why tea can feel calmer than coffee despite containing caffeine. Supplements isolate the L-theanine, so they contain no caffeine.
Found in Camellia sinensis leaves.
Evidence: establishedStudied for effects on brain activity and relaxation.
Evidence: human and animal studiesSupplements contain L-theanine without caffeine.
Evidence: label ingredientsStudied for calm alertness, not sleepiness.
Evidence: human trialsL-theanine and stress: what the trials show
Most L-theanine research looks at short-term stress responses in healthy people. The results are encouraging but small-scale.
Williams et al.: 9 studies
Concluded that 200 to 400 mg a day "may assist in the reduction of stress and anxiety in people exposed to stressful conditions", and called for longer, larger trials.[1]
Williams JL et al. Plant Foods Hum Nutr. 2020;75:12-23.
Kimura et al.: 12 adults, lab stressor
Taken before a mental arithmetic task, L-theanine reduced heart rate and salivary immunoglobulin A responses compared with placebo.[2]
Kimura K et al. Biol Psychol. 2007;74(1):39-45. PMID 16930802.
White et al.: 34 adults, cortisol
An L-theanine-based drink reduced self-rated stress 1 hour after dosing and the salivary cortisol response 3 hours after dosing. The drink had other ingredients, so the effect is not L-theanine alone.[3]
White DJ et al. Nutrients. 2016;8(1):53. PMID 26797633.
Hidese et al.: 30 adults, 4 weeks
200 mg a day at bedtime improved stress-related scores, sleep quality and verbal fluency from baseline. Differences from placebo were not significant for the overall scores. Funded by an L-theanine manufacturer.[4]
Hidese S et al. Nutrients. 2019;11(10):2362. PMID 31623400.
Sarris et al.: 46 adults with GAD
450 to 900 mg a day for 8 weeks, added to an antidepressant, did not reduce anxiety more than placebo (p = 0.73). People on L-theanine reported more sleep satisfaction on one item (p = 0.015).[5]
Sarris J et al. J Psychiatr Res. 2019;110:31-37.
- Best fit: everyday stressful situations in healthy adults.
- Not a fit: diagnosed anxiety disorders, where the main trial was negative.
- Realistic expectation: a subtle "calmer but alert" effect, not a dramatic change.
Stimulant-free supplements for stress and cortisol: how they compare
A common question from people working long hours is what they can take for stress that will not add to their caffeine load. These are the main stimulant-free options and what the evidence says about each.
| Option | Stress or cortisol evidence | EU claim? |
|---|---|---|
|
L-theanine 200–400 mg/day |
Review of 9 studies: may reduce stress under stressful conditions. Null in diagnosed GAD. | None |
|
Phosphatidylserine 400 mg/day in trial |
Normalised ACTH and cortisol responses in the most stressed men in one 42-day trial (n = 75). PS guide | None |
| Ashwagandha | The most-trialled herb for stress, but under safety review in several EU countries. Ashwagandha guide | None |
| Rhodiola | Studied for stress-related fatigue. Rhodiola guide | None |
|
Magnesium ≥15% NRV per serving |
Contributes to normal psychological function and to the reduction of tiredness and fatigue. Magnesium guide | Yes |
- Want calm focus during the working day? L-theanine, alone or with your usual coffee.
- Interested in the cortisol research? Swanson Phosphatidylserine 100mg; the trial dose was 400 mg a day.
- Want the only option with authorised claims? NOW Magnesium Bisglycinate, 200 mg magnesium (53% NRV) per 2 tablets.
The magnesium statements are authorised EU health claims for magnesium as a nutrient, not claims for L-theanine, phosphatidylserine or any combination.
L-theanine and caffeine: the "calm focus" combination
The strongest short-term evidence for L-theanine is in combination with caffeine.
Owen et al.: 27 adults
100 mg L-theanine with 50 mg caffeine improved speed and accuracy on an attention-switching task at 60 minutes, and reduced distraction in a memory task.[6]
Owen GN et al. Nutr Neurosci. 2008;11(4):193-198. PMID 18681988.
Camfield et al.: 11 studies
Moderate benefits for alertness and attention switching in the first 2 hours with caffeine plus L-theanine. Caffeine dose may matter more than the L-theanine dose.[7]
Camfield DA et al. Nutr Rev. 2014;72(8):507-522. PMID 24946991.
The pairing is optional. If you want a fully stimulant-free routine, take L-theanine on its own.
Does L-theanine help with sleep?
L-theanine is often sold for sleep, but it is not a sleeping tablet. The evidence is suggestive, not proven.
- Hidese 2019: 200 mg at bedtime for 4 weeks improved sleep scores from baseline; the overall difference from placebo was not significant.
- Sarris 2019: more sleep satisfaction on one questionnaire item, no difference in overall insomnia severity.
- Lyon 2011: boys aged 8 to 12 with ADHD taking 400 mg a day showed improvements in some objective sleep measures.[8] This was a clinical paediatric group; it does not tell us about adults.
Also looking at sleep? Our magnesium for sleep Ireland guide covers magnesium glycinate.
L-theanine dosage and timing
| Daily amount | Where it was used |
|---|---|
| 100 mg | With 50 mg caffeine for focus (Owen 2008) |
| 200 mg | One NOW capsule; Hidese 4-week trial |
| 200–400 mg | Range in the 2020 stress review; up to 2 NOW capsules |
| 450–900 mg | GAD trial (no benefit over placebo); above the NOW label serving |
The NOW label serving is 1 capsule (200 mg), once or twice a day, preferably on an empty stomach. For the working day, many people take one in the morning or before a demanding task. Do not exceed the label dose.
How long does L-theanine take to work?
L-theanine side effects and safety
- Natural part of tea. The human trials reviewed here used 200 mg a day for 4 weeks and up to 900 mg a day for 8 weeks.
- No EU upper limit has been set, and long-term data at high doses are limited.
- Driving and machinery: it is not a sedative, but see how you respond before combining it with anything that causes drowsiness.
- are pregnant or breastfeeding
- take blood pressure medication, sedatives or other prescription medicines
- have a diagnosed anxiety disorder or depression
- are under 18
Buying L-theanine in Ireland: rules, VAT and delivery
- Legal to buy. L-theanine is sold in Ireland as a food supplement under FSAI rules.[10] It is not a medicine and needs no prescription.
- No authorised health claim. EFSA assessed proposed L-theanine claims for cognitive function, psychological stress, sleep and menstrual discomfort in 2011,[9] and none was authorised under Regulation (EC) No 1924/2006.
- FSAI notification is not approval. The FSAI states notification is not an approval or authorisation process.[11]
- 13.5% VAT. Food supplements carry Ireland's reduced VAT rate.[12]
- No customs from us. Stock ships from Dublin. Orders from outside the EU can attract VAT and customs charges (see customs charges Ireland).
- What to check on a label: mg of L-theanine per capsule, other ingredients, and whether caffeine is added.
Product details were checked by Probiotic.ie on 14 October 2026 against our live product pages: NOW Foods L-Theanine 200 mg Double Strength (200 mg L-theanine and 100 mg inositol per hypromellose capsule; 120 capsules; 1 capsule 1 to 2 times daily, preferably on an empty stomach; no caffeine); Swanson Phosphatidylserine 100mg (30 softgels); NOW Magnesium Bisglycinate (200 mg magnesium, 53% NRV, per 2 tablets; 180 tablets). Always check the label on the pack you receive.
The research discussed in this article relates to L-theanine and phosphatidylserine as studied compounds and should not be read as a claim that any product sold by Probiotic.ie produces these effects. These products are food supplements, not medicines. The only authorised health claims on this page are for magnesium, at the stated amount in NOW Magnesium Bisglycinate.
Ready to order? NOW Foods L-Theanine 200 mg
Caffeine-free L-theanine, one vegan capsule once or twice a day, 120 capsules.
Current price on the product page, including Irish VAT at 13.5%. Food supplement, not a medicine. Interested in cortisol research? View Swanson Phosphatidylserine.
Frequently asked questions
What is L-theanine?
L-theanine is an amino acid found naturally in tea leaves (Camellia sinensis). It is not one of the amino acids the body uses to build protein. As a supplement it is sold in Ireland as a food supplement, usually in 100 mg or 200 mg capsules, and contains no caffeine. No EU health claim is authorised for L-theanine.
What are the best stimulant-free supplements for stress?
The stimulant-free options with the most human research on stress responses are L-theanine, phosphatidylserine and ashwagandha. L-theanine at 200 to 400 mg a day was linked to lower stress and anxiety in people under stressful conditions in a 2020 systematic review of 9 studies (Williams et al., Plant Foods Hum Nutr). Phosphatidylserine at 400 mg a day normalised cortisol responses in the most stressed men in one trial. Ashwagandha is under EU safety review. Magnesium is the only one with authorised EU claims: it contributes to normal psychological function and to the reduction of tiredness and fatigue. None of these is a treatment for stress or anxiety.
Does L-theanine help with stress?
Small trials suggest it can reduce stress responses. In a lab study of 12 adults, L-theanine reduced heart rate and salivary immunoglobulin A responses to a mental arithmetic stressor (Kimura et al., Biol Psychol, 2007). A 2020 review of 9 studies concluded 200 to 400 mg a day "may assist in the reduction of stress and anxiety in people exposed to stressful conditions", but called for larger, longer trials. No EU health claim is authorised for L-theanine and stress.
Does L-theanine lower cortisol?
The cortisol evidence is limited. In a crossover trial of 34 healthy adults, an L-theanine-based drink reduced the salivary cortisol response to a stressor 3 hours after dosing (White et al., Nutrients, 2016). The drink contained other ingredients, so the effect cannot be attributed to L-theanine alone. Phosphatidylserine has more direct cortisol research; see our phosphatidylserine Ireland guide.
Does L-theanine help with anxiety?
Not for diagnosed anxiety disorders, based on current evidence. In a randomised trial of 46 adults with generalised anxiety disorder, 450 to 900 mg of L-theanine a day added to an antidepressant did not reduce anxiety more than placebo (p = 0.73) (Sarris et al., J Psychiatr Res, 2019). Anyone with persistent anxiety should speak to their GP. L-theanine is a food supplement, not a treatment.
Should I take L-theanine with coffee?
Many people do. In a crossover trial of 27 adults, 100 mg L-theanine with 50 mg caffeine improved speed and accuracy on an attention-switching task at 60 minutes (Owen et al., Nutr Neurosci, 2008). A meta-analysis of 11 studies found moderate benefits for alertness and attention in the first 2 hours, with caffeine dose possibly mattering more than the L-theanine dose (Camfield et al., Nutr Rev, 2014). If you want a fully stimulant-free routine, take L-theanine on its own.
Does L-theanine help you sleep?
It is not a sedative. In a 4-week trial of 30 adults taking 200 mg at bedtime, sleep quality scores improved from baseline, but the difference from placebo was not statistically significant overall (Hidese et al., Nutrients, 2019). In the anxiety trial, people taking L-theanine reported greater sleep satisfaction on one questionnaire item. Evidence for sleep is suggestive, not established.
How much L-theanine should I take?
Most human research uses 200 to 400 mg a day. The NOW Foods L-Theanine label serving is one 200 mg capsule, once or twice a day, preferably on an empty stomach, so 200 to 400 mg a day. Single-dose stress studies measured effects within 1 to 3 hours. Do not exceed the label dose.
How long does L-theanine take to work?
In single-dose studies, effects were measured 1 to 3 hours after taking it. The Hidese trial assessed daily use over 4 weeks. Effects are subtle for many people, so judge it over a couple of weeks with your caffeine intake and bedtime kept the same.
Is L-theanine safe? Can I take it every day?
L-theanine is a natural component of tea, and the human trials reviewed here used 200 mg a day for 4 weeks and up to 900 mg a day for 8 weeks. No EU tolerable upper intake level has been set for L-theanine, and long-term safety data at high doses are limited. Check with your GP or pharmacist first if you are pregnant or breastfeeding, take blood pressure medication, sedatives or other prescription medicines.
Is L-theanine legal in Ireland?
Yes. L-theanine is sold in Ireland as a food supplement under FSAI rules and is not a medicine. EFSA assessed proposed L-theanine claims for cognitive function, psychological stress, sleep and menstrual discomfort in 2011 (EFSA Journal 2011;9(6):2238), and none was authorised, so no product can lawfully claim it relieves stress or improves sleep. Food supplements carry 13.5% VAT in Ireland.
Where can I buy L-theanine in Ireland?
Probiotic.ie stocks NOW Foods L-Theanine 200 mg Double Strength: 200 mg L-theanine and 100 mg inositol per vegan capsule, 120 capsules, no caffeine. It ships from Dublin with tracked delivery and no customs charges, and delivery is free on Republic of Ireland orders over €75.
- L-theanine is a caffeine-free amino acid from tea leaves, sold in Ireland as a food supplement under FSAI rules.
- No EU health claim is authorised for L-theanine; EFSA assessed stress, sleep and cognitive claims in 2011 and none was authorised.
- A 2020 systematic review of 9 studies concluded 200 to 400 mg a day may help reduce stress in people under stressful conditions (Williams et al., Plant Foods Hum Nutr).
- In 46 adults with generalised anxiety disorder, 450 to 900 mg a day did not beat placebo (Sarris et al., J Psychiatr Res, 2019).
- With caffeine, L-theanine improved attention in the first 2 hours in a meta-analysis of 11 studies (Camfield et al., Nutr Rev, 2014).
- Sleep evidence is suggestive, not established; L-theanine is not a sedative.
- Stimulant-free alternatives include phosphatidylserine and magnesium; magnesium is the only one with authorised EU claims.
- Probiotic.ie stocks NOW Foods L-Theanine 200 mg (120 vegan capsules), shipped from Dublin with no customs charges.
More evidence guides from Probiotic.ie
This guide was first published on 27 February 2026 and rebuilt by Probiotic.ie on 14 October 2026. In the review we:
- Replaced unclear source links with named human studies, each checked against PubMed or publisher records.
- Added conflicting evidence (Sarris 2019, negative for diagnosed anxiety) and noted industry funding where reported.
- Added a stimulant-free comparison covering phosphatidylserine, ashwagandha, rhodiola and magnesium.
- Removed prices from the article and checked product details against our live product pages.
- Checked FSAI rules and confirmed no EU health claim is authorised for L-theanine.
- Made no disease-treatment claims and no health claims for L-theanine.
This guide has not been reviewed by a clinician. It is not medical advice.
Sources
- [1] Williams JL, Everett JM, D'Cunha NM, 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;75:12-23. — doi.org/10.1007/s11130-019-00771-5
- [2] Kimura K, Ozeki M, Juneja LR, Ohira H. L-Theanine reduces psychological and physiological stress responses. Biol Psychol. 2007;74(1):39-45. PMID 16930802. — pubmed.ncbi.nlm.nih.gov/16930802
- [3] White DJ et al. Anti-stress, behavioural and magnetoencephalography effects of an L-theanine-based nutrient drink: a randomised, double-blind, placebo-controlled, crossover trial. Nutrients. 2016;8(1):53. PMID 26797633. — pubmed.ncbi.nlm.nih.gov/26797633
- [4] 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;11(10):2362. PMID 31623400. — pubmed.ncbi.nlm.nih.gov/31623400
- [5] Sarris J, Byrne GJ, Cribb L, et al. L-theanine in the adjunctive treatment of generalized anxiety disorder: a double-blind, randomised, placebo-controlled trial. J Psychiatr Res. 2019;110:31-37. — researchers.westernsydney.edu.au
- [6] Owen GN, Parnell H, De Bruin EA, Rycroft JA. The combined effects of L-theanine and caffeine on cognitive performance and mood. Nutr Neurosci. 2008;11(4):193-198. PMID 18681988. — pubmed.ncbi.nlm.nih.gov/18681988
- [7] Camfield DA, Stough C, Farrimond J, Scholey AB. Acute effects of tea constituents L-theanine, caffeine, and epigallocatechin gallate on cognitive function and mood: a systematic review and meta-analysis. Nutr Rev. 2014;72(8):507-522. PMID 24946991. — pubmed.ncbi.nlm.nih.gov/24946991
- [8] 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):348-354. PMID 22214254. — pubmed.ncbi.nlm.nih.gov/22214254
- [9] EFSA NDA Panel. 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 menstrual discomfort pursuant to Article 13(1) of Regulation (EC) No 1924/2006. EFSA Journal. 2011;9(6):2238. — efsa.europa.eu
- [10] Food Safety Authority of Ireland. Food Supplements: legislation and guidance. — fsai.ie/legislation/food-legislation/food-supplements
- [11] Food Safety Authority of Ireland. Food Supplements – Legislative Requirements. 2024. — fsai.ie (PDF)
- [12] Revenue Commissioners. Tax and Duty Manual: VAT treatment of food supplement products. — revenue.ie (PDF)