L-Theanine
⏱ 12 min read
L-theanine (also written l-theanine or theanine) is a non-proteinogenic amino acid found naturally in the leaves of green tea (Camellia sinensis). The properties and benefits of L-theanine have been the subject of one of the broadest bodies of clinical research among tea compounds, covering relaxation without drowsiness, support for subclinical anxiety, subjective sleep quality and attention and focus parameters (especially in combination with caffeine). The L-theanine in the PLENIAGE® L-Theanine supplement comes from a Camellia sinensis (L.) Kuntze extract standardised to 40% theanine and free of EGCG (epigallocatechin gallate), a green tea polyphenol that EFSA regulated in 2018 over the risk of hepatotoxicity at high doses. This page covers what it is used for, how it works, the studied doses, safety considerations and where it fits within the Pleniage portfolio.
On this page
What is L-theanine?
The L-theanine in the PLENIAGE® supplement
How it works: GABA, glutamate and alpha brain waves
Clinical evidence: relaxation, sleep and attention
Studied doses and time of day
L-theanine and caffeine: the most studied combination
Green tea, EGCG and the product's pure L-theanine
Safety and interactions
How to choose an L-theanine supplement
L-theanine in the Pleniage portfolio
Frequently asked questions
References
What is L-theanine?
L-theanine (γ-glutamylethylamide) is a non-proteinogenic amino acid, meaning it is not incorporated into proteins the way the 20 classic essential and non-essential amino acids are, and does not build tissue. Its biological role is related more to neurotransmitter modulation than to tissue construction. It is found mainly in the leaves of green tea (Camellia sinensis), where it can represent between 1% and 2% of dry weight depending on the variety and growing conditions.
Structurally, L-theanine is similar to glutamate, the main excitatory neurotransmitter of the central nervous system, and to GABA (gamma-aminobutyric acid), the main inhibitory neurotransmitter. This structural similarity underlies the modulatory effects on the nervous system documented in clinical research.
The L-theanine in the PLENIAGE® supplement
The L-theanine used in PLENIAGE® supplements is a natural green tea leaf extract (Camellia sinensis (L.) Kuntze) standardised to 40% theanine and with an EGCG-free profile (epigallocatechin gallate). This distinction matters because of the safety considerations associated with concentrated EGCG, discussed in the dedicated section below. Likewise, the L-theanine used in PLENIAGE products contains no caffeine, which adds flexibility of use as described below.
How it works: GABA, glutamate and alpha brain waves
Simplified scheme: L-theanine modulates the GABA/glutamate balance and promotes the appearance of alpha brain waves (8-13 Hz) — an EEG pattern associated with a state of "calm focus", distinct from drowsiness (theta waves) or deep sleep (delta waves).
L-theanine crosses the blood-brain barrier after oral administration, reaching the central nervous system directly. The mechanisms described in clinical and preclinical research are three main ones:
Modulation of the GABA/glutamate balance: L-theanine moderately increases GABA availability and partially attenuates excitatory glutamatergic transmission. The net result is a modulatory effect, not a properly sedative one.
Promotion of alpha brain waves (8-13 Hz): electroencephalographic (EEG) recordings in humans show an increase in alpha activity after oral administration of 200 mg of L-theanine, according to studies by Nobre and colleagues. Alpha waves are associated with a state of "calm focus" characteristic of meditation or calm without loss of cognitive capacity, distinct from drowsiness (theta waves) or deep sleep (delta waves).
Modulation of dopamine and serotonin in specific brain regions, according to preclinical data in animal models. The clinical translation of this mechanism is less firmly established.
Clinical evidence: relaxation, sleep and attention
The broadest body of clinical evidence in humans on L-theanine covers three related areas:
Relaxation and stress response
The trial by Hidese and colleagues published in Nutrients in 2019 studied 30 adults with self-reported stress complaints, assigned to receive 200 mg/day of L-theanine or placebo for 4 weeks. The L-theanine group documented decreases on the STAI scale (State-Trait Anxiety Inventory) and improvements on subjective sleep-quality scales relative to baseline and placebo.
The meta-analysis by Williams and colleagues published in Plant Foods for Human Nutrition in 2020 synthesised the available evidence on L-theanine and stress response and concluded a consistent effect of small-to-moderate magnitude, with good tolerability across all the trials reviewed.
Subjective sleep quality
The review by Lyon and colleagues published in Alternative Medicine Review documented improvements in subjective sleep quality with doses of 200-400 mg/day of L-theanine, especially in the "ease of falling asleep" component and the sense of restfulness on waking. Important: L-theanine does not act as a sedative hypnotic; its effect on sleep appears to be mediated by its action on calm and the attenuation of pre-sleep rumination, not by a direct induction of the hypnotic state.
Attention and cognitive performance
The trial by Higashiyama and colleagues published in the Journal of Functional Foods in 2011 documented improvements in sustained-attention markers in young adults after administration of 200 mg of L-theanine, especially in demanding cognitive tasks. This line of evidence is the basis for the L-theanine + caffeine combination described in the next section.
Studied doses and time of day
The doses investigated in the main clinical trials with L-theanine range between 100 mg and 400 mg per day, in a single dose or split into two. The 200 mg/day dose is the most used in trials on relaxation and sleep and the usual standard dose in commercial formulation.
Time of day:
Evening intake (1-2 hours before sleep) is the most used regimen when the goal is support for calm and sleep.
Morning or pre-task intake (with or without caffeine) when the goal is attention and focus without the nervous activation typical of coffee alone.
Split intakes (morning + night) in profiles with sustained stress throughout the day.
L-theanine and caffeine: the most studied combination
The combination of L-theanine (~100 mg) with caffeine (~50-100 mg) is one of the nootropic combinations with the most solid evidence base. Caffeine alone produces attentional activation but also subjective jitteriness, tachycardia and, in some people, anxiety. Added L-theanine attenuates the nervous component of caffeine without reducing its effect on attention, according to trials by Owen and colleagues published in Nutritional Neuroscience.
The subjective result described by participants is "alert but calm", consistent with the EEG pattern documented by Nobre (more alpha waves with the combination than with either compound on its own). This is the rationale behind the natural presence of L-theanine in green tea, where it coexists with caffeine in a balanced way.
Green tea, EGCG and the product's pure L-theanine
Green tea (Camellia sinensis) naturally contains several polyphenols, among them EGCG (epigallocatechin gallate). EFSA issued alerts in 2018 about concentrated green tea extracts with EGCG over the risk of hepatotoxicity (acute hepatitis) at high doses (>800 mg/day), which is why Italy and France regulated these products by restricting the maximum amounts allowed in supplements.
The L-theanine in the PLENIAGE® L-Theanine supplement is a Camellia sinensis extract standardised to 40% theanine free of EGCG, a profile that retains the effects attributed to theanine without the polyphenol load associated with the liver risk described in the EFSA alerts. This distinction matters because some commercial supplements labelled generically as "green tea extract" or "L-theanine" may contain residual EGCG in variable amounts, depending on the extract's production process.
Safety and interactions
L-theanine has a very favourable safety profile at the usual supplementation doses. The FDA (United States) has assigned it GRAS status (Generally Recognized As Safe) and EFSA has not established a specific tolerable upper limit (UL), consistent with the absence of serious adverse events documented in the available clinical literature.
Infrequent adverse effects
Mild drowsiness: very infrequent at usual doses; it may appear with high evening doses (≥400 mg) in sensitive individuals.
Mild headache: reported sporadically in clinical trials, with no significant difference from placebo.
Mild hypotension in predisposed individuals or those treated with antihypertensives; clinically of little relevance at standard doses.
Drug interactions
Antihypertensives: possible mild potentiation of the hypotensive effect.
Sedatives and anxiolytics (benzodiazepines, hypnotics): an additive effect is possible; not contraindicated, but it is advisable to discuss it with your doctor if they are used together.
Stimulants (caffeine, theobromine): the combination with caffeine is the most studied and has a favourable profile; with other stimulants there is less data.
Specific contraindications
Pregnancy and breastfeeding: as a general precaution, in the absence of sufficient human data in these contexts, specific L-theanine supplementation is best avoided (beyond the natural intake from moderate tea consumption) unless medically advised.
Scheduled surgery: because of its effect on the central nervous system, it is advisable to stop at least 2 weeks before surgery.
How to choose an L-theanine supplement
Declared source and standardisation: prioritise products that declare the botanical source (Camellia sinensis extract or specific origin) and the theanine percentage of the extract.
EGCG profile: prioritise products that explicitly declare "EGCG-free" or that provide certificates of analysis confirming absence/trace amounts, especially for chronic use.
Dose consistent with the evidence: 100-200 mg per recommended dose covers most of the range used in clinical trials. Doses >400 mg/day fall outside the usually studied profile.
L-theanine vs DL-theanine: prioritise the L- form, which is the one naturally present in tea and used in most clinical trials. The DL- form (synthetic racemic mixture) has less research support.
Traceability and third-party certificates of analysis when available.
L-theanine in the Pleniage portfolio
L-theanine is part of the Pleniage portfolio in two complementary formulations:
PLENIAGE® L-Theanine (single-ingredient): Camellia sinensis extract standardised to 40% theanine, EGCG-free. For flexible use when seeking the specific amino acid input without combining it with other adaptogens.
PLENIAGE® PRO CALM+: a compound formula that includes the same L-theanine (EGCG-free) together with Magnesium bisglycinate Albion TRAACS®, Ashwagandha KSM-66 BIO, Rhodiola at 3% rosavins and B-group vitamins (B6, B9, B12). For profiles seeking broad support for the nervous system, calm and sleep in a single formula. Each ingredient has its own individual scientific research.
This page is part of the Calm and Balance cluster. To explore other related components, see the Ashwagandha KSM-66 page and the Magnesium bisglycinate page.
Frequently asked questions about L-theanine
Does L-theanine make you sleepy or relax you without sleeping?
L-theanine does not act as a sedative hypnotic. Its characteristic effect, documented in human EEG recordings, is the promotion of alpha brain waves (8-13 Hz) associated with a state of "calm focus" — calm without loss of cognitive capacity. It is distinct from drowsiness (theta waves) or deep sleep (delta waves). The effect on subjective sleep quality appears to be mediated by the attenuation of pre-sleep rumination and the ease of falling asleep, not by a direct hypnotic induction.
What does the L-theanine with caffeine combination do?
It is one of the nootropic combinations with the most solid evidence base. L-theanine (~100 mg) attenuates the nervous component of caffeine (~50-100 mg) without reducing its effect on attention. The subjective result described by participants in studies is "alert but calm", consistent with the EEG pattern (more alpha waves with the combination than with either compound on its own). This is the rationale behind the natural presence of L-theanine in green tea, where it coexists with caffeine in a balanced way.
Why does it matter that the L-theanine is EGCG-free?
Green tea naturally contains several polyphenols, among them EGCG (epigallocatechin gallate). EFSA issued alerts in 2018 about concentrated green tea extracts with EGCG over the risk of hepatotoxicity at high doses (>800 mg/day), which is why Italy and France regulated these products. The L-theanine in the PLENIAGE® supplement is a Camellia sinensis extract free of EGCG, a profile that retains the effects attributed to theanine without the polyphenol load associated with the liver risk. Other generic "L-theanine" supplements may contain residual EGCG in variable amounts.
How long does L-theanine take to be noticeable?
The acute effect (calm, attention) may be felt 30-60 minutes after intake. The effects on subjective sleep quality and chronic stress response are documented in clinical trials from 2-4 weeks of continued use. If after 4-6 weeks no relevant subjective changes are noticed, it is advisable to review the dose, the regimen or to seek advice to rule out other causes of the original problem.
What is the standard dose of L-theanine?
200 mg/day is the most used dose in clinical trials on relaxation and sleep and the usual standard dose in commercial formulation. The investigated range goes from 100 to 400 mg/day. The dose for combining with caffeine is usually ~100 mg of L-theanine with ~50-100 mg of caffeine.
Does it have contraindications or interactions?
L-theanine has a very favourable safety profile (FDA GRAS status, no EFSA UL). It has no absolute contraindications beyond pregnancy/breastfeeding and scheduled surgery (stop at least 2 weeks before). The relevant interactions are mild: possible potentiation of the hypotensive effect of antihypertensives, an additive effect with sedatives and anxiolytics (not contraindicated, but worth discussing with your doctor if used together). The adverse effects described are infrequent and mild.
Can I take L-theanine together with magnesium?
Yes. The combination of L-theanine with magnesium (especially bisglycinate) has a coherent rationale — both act on the nervous system through complementary mechanisms (L-theanine on the GABA/glutamate balance and alpha waves; magnesium as an enzymatic cofactor with a modulatory effect) and share a profile oriented towards calm and sleep. This is the rationale behind the PRO CALM+ formula. There are no documented drug interactions between the two.
L-theanine is a non-proteinogenic amino acid abundant in the leaves of green tea (Camellia sinensis), with a consolidated body of clinical evidence on calm focus, subjective sleep quality and sustained attention. The form used in PLENIAGE® supplements is an extract at 40% theanine free of EGCG, a profile that retains the effects attributed to theanine without the polyphenol load associated with the liver risk documented by EFSA in concentrated green tea extracts with EGCG.
At PLENIAGE® we publish scientific content on evidence-based supplementation. You can explore the Calm and Balance cluster for more related pages and articles.
References
The statements in this article are based on the available scientific literature and the relevant official records (EFSA EGCG alerts 2018, FDA GRAS status for L-theanine).
Hidese S, Ogawa S, Ota M, 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.
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(1):12-23. PMID: 31758301.
Higashiyama A, Htay HH, Ozeki M, Juneja LR, Kapoor MP. Effects of l-theanine on attention and reaction time response. J Funct Foods. 2011;3(3):171-178. DOI: 10.1016/j.jff.2011.03.009.
Nobre AC, Rao A, Owen GN. L-theanine, a natural constituent in tea, and its effect on mental state. Asia Pac J Clin Nutr. 2008;17 Suppl 1:167-168. PMID: 18296328.
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.
EFSA Panel on Food Additives and Nutrient Sources added to Food. Scientific opinion on the safety of green tea catechins. EFSA Journal. 2018;16(4):5239. EFSA Journal 2018 (EGCG and hepatotoxicity alert).
This content is for informational and educational purposes. It does not replace the advice of a healthcare professional. As a general precaution, specific L-theanine supplementation is best avoided during pregnancy and breastfeeding unless medically advised, and stopped at least 2 weeks before any scheduled surgery.
Last reviewed: 01/06/2026