L-theanine is an amino acid found in tea leaves. A meta-analysis of 18 trials found it produces small improvements in how people rate their sleep quality, how quickly they feel they fall asleep, and how they function the next day (Bulman et al., 2025). It is not a sedative, and it has not been shown to treat insomnia.
Below is what the research supports, what it does not, and how to use it.
What is L-theanine?
L-theanine is an amino acid that occurs almost only in the tea plant, Camellia sinensis. It is the compound usually credited with the calm that tea drinkers describe, as distinct from the lift of caffeine.
A standard 200ml cup of black tea contains about 24mg of L-theanine and a cup of green tea about 8mg, depending heavily on the tea and how long it is brewed (Keenan et al., 2011). Across commercial teas the content varies widely within each type (Boros, Jedlinszki and Csupor, 2016).
A 200mg supplement dose is therefore the equivalent of roughly eight cups of black tea, without the caffeine.
What the research says about L-theanine and sleep
The pooled evidence
The largest analysis to date combined 18 randomised trials. L-theanine improved self-rated sleep quality, self-rated time to fall asleep and daytime functioning compared with placebo. The effects were small, the improvement in time to fall asleep was the smallest of the three, and many of the trials tested L-theanine combined with other ingredients (Bulman et al., 2025).
A separate systematic review looked only at trials of L-theanine alone: 13 studies and 550 participants. It concluded that 200 to 450mg a day appears to be a safe and effective way to support healthy sleep in adults, and called for more trials using objective sleep measurement (Cotter et al., 2026).
The trial closest to how people actually use it
In a four-week crossover trial, 30 healthy adults took 200mg of L-theanine before bed each night. Compared with placebo, scores for time to fall asleep, sleep disturbance and use of sleep medication improved. The overall sleep quality score moved in the right direction but did not reach statistical significance against placebo. Scores for trait anxiety and depressive symptoms fell during the L-theanine period (Hidese et al., 2019).
The authors themselves noted that the effects were not large. The study was funded by an L-theanine manufacturer.
Trials that found little or nothing
It is worth being straight about the null results.
- In 46 adults with generalised anxiety disorder, 450 to 900mg a day for eight weeks did not beat placebo on anxiety or on insomnia severity. Participants did report better sleep satisfaction (Sarris et al., 2019).
- In 30 moderately stressed adults taking 400mg a day for 28 days, perceived stress fell by about 18% in both the L-theanine and placebo groups, and questionnaire measures of sleep did not differ between them (Moulin et al., 2024).
- In 98 boys with ADHD, 400mg a day improved sleep efficiency measured by wrist monitor, but did not change how long they took to fall asleep (Lyon, Kapoor and Juneja, 2011).
One recent review summed up the field by saying the science does not yet match the hype (Dashwood and Visioli, 2025).
How might L-theanine work?
Relaxed, not drowsy
The best-known finding is that L-theanine increases alpha brain-wave activity, a pattern associated with being awake but relaxed. This was seen with a 50mg dose (Nobre, Rao and Owen, 2008) and with 200mg under mental stress, where it also lowered the stress hormone cortisol in saliva one hour later (Evans et al., 2021).
Alpha activity reflects calm wakefulness, not sleep. That fits the idea, put forward in a review by researchers at an L-theanine manufacturer, that it supports sleep by easing tension and not by sedating (Rao, Ozeki and Juneja, 2015).
Stress responses
In a small laboratory study, L-theanine reduced the rise in heart rate caused by a stressful mental arithmetic task (Kimura et al., 2007). A meta-analysis of 31 trials found a modest reduction in acute stress after a single dose, while noting that the result leaned on lower-quality studies and that effects on anxiety were inconsistent (Gerolymos et al., 2026). An earlier systematic review concluded that 200 to 400mg a day may help reduce stress and anxiety in people under stressful conditions (Williams et al., 2020).
Brain chemistry
In rats, L-theanine crosses the blood-brain barrier and alters levels of dopamine and serotonin (Yokogoshi et al., 1998). In cell studies it interferes with the transport of glutamine, the raw material for the excitatory messenger glutamate (Kakuda et al., 2008). These findings come from animals and cell cultures, often at concentrations far above those reached in human blood, so they suggest how it might work without proving it.
How much, and when?
Dose. Reviews point to 200 to 450mg a day for sleep (Cotter et al., 2026) and 200 to 400mg for stress (Williams et al., 2020). OFFLINE Sleep contains 200mg, the dose used before bed in the Hidese trial.
Timing. L-theanine is absorbed quickly. Blood levels peak about 50 minutes after taking it, whether from capsules or tea (van der Pijl, Chen and Mulder, 2010; Scheid et al., 2012). That makes 30 to 45 minutes before bed a reasonable window, though no trial has directly compared different timings.
It is also cleared quickly, with an elimination half-life of around 65 minutes (van der Pijl, Chen and Mulder, 2010). This is one reason it is unlikely to linger into the morning.
Is it safe?
In trials, L-theanine has been well tolerated at up to 900mg a day for eight weeks (Sarris et al., 2019). A meta-analysis of 31 randomised trials reported no serious adverse events (Gerolymos et al., 2026). In one study two mild effects, a metallic taste and a dry mouth, were judged possibly related (Moulin et al., 2024).
A 13-week toxicity study in rats found no adverse effects at the highest dose tested, 4,000mg per kilogram of body weight a day (Borzelleca, Peters and Hall, 2006).
What is missing is long-term human data and formal studies of drug interactions. If you take prescription medicine, particularly for blood pressure or sleep, or are pregnant or breastfeeding, check with your doctor or pharmacist first.
Frequently asked questions
Will L-theanine knock me out? No. Its measurable effects are on relaxation while awake. Trials have not reported daytime drowsiness as a problem, and the pooled data show better daytime functioning (Bulman et al., 2025).
Can I just drink tea before bed? You would need about eight cups of black tea to reach 200mg (Keenan et al., 2011), and you would be taking in a lot of caffeine with it.
How long before I notice anything? Single doses change stress markers within one to three hours (Evans et al., 2021). The sleep trials ran for four weeks or longer.
Does it help with anxiety? It may ease everyday stress. It did not outperform placebo in people with a diagnosed anxiety disorder (Sarris et al., 2019), and it is not a treatment for one.
The bottom line
L-theanine is one of the better-studied calming supplements. The benefits for sleep are real in pooled data but small, and they show up in how people feel about their sleep more than in objective measurements. It suits people whose problem is a busy head at bedtime, which is why it is in OFFLINE Sleep at 200mg, alongside four other ingredients.
This article is for general information and is not medical advice. Food supplements are not a substitute for a varied diet. If you have ongoing sleep problems or anxiety, speak to your GP.
References
Boros, K., Jedlinszki, N. and Csupor, D. (2016) 'Theanine and caffeine content of infusions prepared from commercial tea samples', Pharmacognosy Magazine, 12(45), pp. 75–79. doi:10.4103/0973-1296.176061.
Borzelleca, J.F., Peters, D. and Hall, W. (2006) 'A 13-week dietary toxicity and toxicokinetic study with L-theanine in rats', Food and Chemical Toxicology, 44(7), pp. 1158–1166. doi:10.1016/j.fct.2006.03.014.
Bulman, A., D'Cunha, N.M., Marx, W., Turner, M., McKune, A. and Naumovski, N. (2025) 'The effects of L-theanine consumption on sleep outcomes: a systematic review and meta-analysis', Sleep Medicine Reviews, 81, 102076. doi:10.1016/j.smrv.2025.102076.
Cotter, J., Caddick, C.E., Harper, J.L. and Ebajemito, J.K. (2026) 'Examining the effect of L-theanine on sleep: a systematic review of dietary supplementation trials', Nutritional Neuroscience, 29(2), pp. 224–238. doi:10.1080/1028415X.2025.2556925.
Dashwood, R. and Visioli, F. (2025) 'L-theanine: from tea leaf to trending supplement – does the science match the hype for brain health and relaxation?', Nutrition Research, 134, pp. 39–48. doi:10.1016/j.nutres.2024.12.008.
Evans, M., McDonald, A.C., Xiong, L., Crowley, D.C. and Guthrie, N. (2021) 'A randomized, triple-blind, placebo-controlled, crossover study to investigate the efficacy of a single dose of AlphaWave® L-theanine on stress in a healthy adult population', Neurology and Therapy, 10(2), pp. 1061–1078. doi:10.1007/s40120-021-00284-x.
Gerolymos, C., Saddier, E., Boyer, L. and Fond, G. (2026) 'Cognitive and affective effects of L-theanine: a systematic review and meta-analysis of 31 randomized trials', Molecular Psychiatry [Preprint]. doi:10.1038/s41380-026-03727-9.
Hidese, S., Ogawa, S., Ota, M., Ishida, I., Yasukawa, Z., Ozeki, M. and Kunugi, H. (2019) 'Effects of L-theanine administration on stress-related symptoms and cognitive functions in healthy adults: a randomized controlled trial', Nutrients, 11(10), 2362. doi:10.3390/nu11102362.
Kakuda, T., Hinoi, E., Abe, A., Nozawa, A., Ogura, M. and Yoneda, Y. (2008) 'Theanine, an ingredient of green tea, inhibits [3H]glutamine transport in neurons and astroglia in rat brain', Journal of Neuroscience Research, 86(8), pp. 1846–1856. doi:10.1002/jnr.21637.
Keenan, E.K., Finnie, M.D.A., Jones, P.S., Rogers, P.J. and Priestley, C.M. (2011) 'How much theanine in a cup of tea? Effects of tea type and method of preparation', Food Chemistry, 125(2), pp. 588–594. doi:10.1016/j.foodchem.2010.08.071.
Kimura, K., Ozeki, M., Juneja, L.R. and Ohira, H. (2007) 'L-theanine reduces psychological and physiological stress responses', Biological Psychology, 74(1), pp. 39–45. doi:10.1016/j.biopsycho.2006.06.006.
Lyon, M.R., Kapoor, M.P. and Juneja, L.R. (2011) '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', Alternative Medicine Review, 16(4), pp. 348–354.
Moulin, M., Crowley, D.C., Xiong, L., Guthrie, N. and Lewis, E.D. (2024) 'Safety and efficacy of AlphaWave® L-theanine supplementation for 28 days in healthy adults with moderate stress: a randomized, double-blind, placebo-controlled trial', Neurology and Therapy, 13(4), pp. 1135–1153. doi:10.1007/s40120-024-00624-7.
Nobre, A.C., Rao, A. and Owen, G.N. (2008) 'L-theanine, a natural constituent in tea, and its effect on mental state', Asia Pacific Journal of Clinical Nutrition, 17(Suppl. 1), pp. 167–168.
Rao, T.P., Ozeki, M. and Juneja, L.R. (2015) 'In search of a safe natural sleep aid', Journal of the American College of Nutrition, 34(5), pp. 436–447. doi:10.1080/07315724.2014.926153.
Sarris, J., Byrne, G.J., Cribb, L., Oliver, G., Murphy, J., Macdonald, P., Nazareth, S., Karamacoska, D., Galea, S., Short, A., Ee, C., Birling, Y., Menon, R. and Ng, C.H. (2019) 'L-theanine in the adjunctive treatment of generalized anxiety disorder: a double-blind, randomised, placebo-controlled trial', Journal of Psychiatric Research, 110, pp. 31–37. doi:10.1016/j.jpsychires.2018.12.014.
Scheid, L., Ellinger, S., Alteheld, B., Herholz, H., Ellinger, J., Henn, T., Helfrich, H.-P. and Stehle, P. (2012) 'Kinetics of L-theanine uptake and metabolism in healthy participants are comparable after ingestion of L-theanine via capsules and green tea', The Journal of Nutrition, 142(12), pp. 2091–2096. doi:10.3945/jn.112.166371.
van der Pijl, P.C., Chen, L. and Mulder, T.P.J. (2010) 'Human disposition of L-theanine in tea or aqueous solution', Journal of Functional Foods, 2(4), pp. 239–244. doi:10.1016/j.jff.2010.08.001.
Williams, J.L., Everett, J.M., D'Cunha, N.M., Sergi, D., Georgousopoulou, E.N., Keegan, R.J., McKune, A.J., Mellor, D.D., Anstice, N. and Naumovski, N. (2020) 'The effects of green tea amino acid L-theanine consumption on the ability to manage stress and anxiety levels: a systematic review', Plant Foods for Human Nutrition, 75(1), pp. 12–23. doi:10.1007/s11130-019-00771-5.
Yokogoshi, H., Kobayashi, M., Mochizuki, M. and Terashima, T. (1998) 'Effect of theanine, r-glutamylethylamide, on brain monoamines and striatal dopamine release in conscious rats', Neurochemical Research, 23(5), pp. 667–673. doi:10.1023/A:1022490806093.