Caffeine and Theanine



7.0 /10


7.0 /10


4.0 /10

Caffeine and Theanine

Boost Energy
Improve Focus
Improve Memory
Pre Workout
Weight Loss
Mood Support



L-theanine, also known as N-ethyl-L-glutamine, is a major non-protein, water soluble [1] amino acid commonly found in green tea [2; 3], and has been the focus of much attention due its role in having positive effects in the brain [2; 4] and body. In green tea, L-theanine has been estimated to be between 1-2% of dry weight tea [5] which is translated as being around 10-30g/kg in green tea leaves [6]– Table 1. In addition, L-theanine has been shown to have antioxidant properties [7], blood pressure lowering attributes; along with possessing neuroprotective effects [7].


Figure 1: Theanine is a chiral compound, occurring in nature as the L-enantiomer. Its IUPAC name id 2-amino-4 butyric acid [8]. L-theanine has a similar chemical structure to L-glutamate – an important neurotransmitter related to memory [9].

Mechanism and interactions

Once consumed, L-theanine rapidly interacts with the intestinal tract, where it is absorbed, as well as being transported into the brain [10;8]. When taken orally, L-theanine takes only an hour to be detected in serum. Within 5 hours L-theanine reaches its maximum level, where it then lasts for 24 hours – having exited the kidneys, liver and brain [11 Other data has suggested that L- theanine, administered to rats, took only 30 minutes to reach the brain [12].

Suntheanine Vs L-theanine

Synthetic l-thanine, also known as Suntheanine, is made up of a ‘mixture’ of the two forms – D and L – of theanine [8]. This commercially branded version of theanine is manufactured and sold as an herbal supplement [11]. Considering that it is not naturally occurring L-theanine, suntheanine requires food-borne L-glutamine and ethylamine, along with the glutaminase enzyme for synthesis [8]. Suntheanine (compared to L-theanine) has also been considered just as beneficial as L-theanine; and, its LD50 (toxic dose index) was found to be greater than 5,000mg/kg [13].

Caffeine and L-theanine

Caffeine (coffee) and L-theanine combinations have been reported to produce faster responses in memory and attention (figure 2.). Also, interactions of caffeine and L-theanine have reported that L-theanine protects against toxic caffeine doses, and stops the exciting effects felt from caffeine [14]. In one study, 50mg of caffeine was used in combination with L-theanine (and also stand-alone) to compare effects on cognition and mood [15]. Synergy between L-theanine and caffeine has been established: Another study, measuring the ratio of caffeine dosage (50mg) with L-theanine dosage (100mg) affecting cognitive function of attention showed an enhancement of attention over a 4-day period [16]. L-theanine and caffeine were also concluded as significantly improving attention during a demanding exercise – this study used a moderate dose of 97mg (L-theanine) and 40mg (caffeine) [17]. Overall, when combined L-theanine and caffeine improve cognitive performance and attention as opposed to their ‘stand-alone’ effects [14]. A 20-person placebo-controlled study using a caffeine-L-theanine combination on cognitive and visual reaction time showed improvements cognition, with L-theanine and caffeine, in synergy, having an additive effect on attention [18].

Figure 2: Data assessment of caffeine and L-theanine direct interactions showed the number of correct responses increased in L-theanine caffeine condition after 60 minutes [15]. The caffeine L-theanine produced faster responses and improved accuracy, along with improving scores in a word recognition test [15]. Caffeine on its own did not improve these aspects [15].

Benefits and Effects

L-theanine has anti-tumour, anti-diabetes, anti-hypertension and anti-stress effects [19; 20]. Additionally, L-theanine prevents nerve cell damage and protects the liver from damage [19]. Along with these benefits, theanine promotes relaxation, improves learning and concentration, improves the immune system and reduces blood pressure [20]. Once consumed, theanine interacts and elicits its effects by passing across the blood brain barrier (BBB) where exerts it’s a range of positive neurophysiological and pharmacological effects [11]. Also, L-theanine has been associated with an increased release and concentration of dopamine, along with blocking glutamate reuptake and glutamate receptors in the hippocampus [21; 22]. Remarkably, L-theanine has also been shown to have an antidepressant-like effect in a dose range between 1-20mg/kg over 10 days in mice. This effect might be mediated through the central nervous system [23].

Figure 3. Described benefits of L-theanine [8]. Several lines of research have documented the positive effects of L-theanine on the brain and body. Apart from having a beneficial effect on stress, L-theanine has been known to exert positive effects and interactions on attention, cancer, cognitive performance and cardiovascular health.

L-theanine and major depressive disorder (MDD)

In a more recent study assessing the effect of L-theanine on patients with depression, L-theanine – in a 250mg/day dose administered over 8 weeks – showed a beneficial outcome in depressive symptoms: anxiety, sleep disturbance and cognitive impairment in all patients [24]. Since 250mg of L-theanine is classed as a high dose, researchers concluded that this high L-theanine dose was highly tolerated [24]. One major finding is that L-theanine has structural similarity to L-glutamate, and therefore mode of action is likely to follow the glutamatergic pathway [24].

L-theanine and ADHD

One study found that L-theanine in studying ADHD, given in a 400mg dose to 8-12-year-old boys, was effective in improving sleep quality [25]. Researchers of this study suggested the importance of considering a 400mg, safe dose in treating childhood ADHD [25] – Figure 4.

Figure 4. Compared to the placebo, L-theanine (400mg dose) improved sleep quality in boys with ADHD [25].

L-theanine effects on sleep

L-theanine was found to improve sleep quality in patients suffering from schizophrenia [26]. An investigation into ADHD-related sleep disorders found that L-theanine did not produce a significant change in total sleep time; however, it did significantly increase sleep efficiency along with a reduction in nocturnal activity [27]. L-theanine promotes the generation of alpha waves in the brain, which creates a relaxed state without the feeling of drowsiness [1].

Figure 5. The effects of suntheanine on sleep quality. Suntheanine has been shown to improve sleep quality compared to placebo. It also provides relaxation, relieves stress, and alleviates anxiety, fatigue and PMS [13].

L-theanine and blood pressure

Animal work has found that L-theanine can reduce blood pressure in hypersensitive rats [28]. This has largely been attributed to the way L-theanine interacts with the autonomic nervous syste, (ANS), where it carries out anti-stress activities [28]. Regulation of blood pressure is dependent on the peripheral nervous system (PNS), and L-theanine alleviates high blood pressure through interacting with several peripheral nervous system pathways and blood vessels – thus, lowering the blood pressure and producing a calming effect [12].

L-theanine in Green tea

L-theanine, along with other constituents, is contained in black tea and green tea. L-Theanine contributes to the sweet taste of green tea [29]. In a 250ml serving of green tea, it has been estimate that around 40mg of L-theanine is contained in this brew [30]. L-theanine constitutes about 1-3% of the dry weight of green tea [31; 10; 11], and around 50% of the total amino acids in green tea leaves [10; 205]. A study seeking to quantify L-theanine in a standard cup of green tea found 7.9mg [32] to be contained to be contained in about 200mL of tea.


Typical doses of between 50-200mg daily is most commonly reported [29]. Studies in rats have demonstrated that up to 4 g/kg per day – considered a high L-theanine dose – had a non-toxic outcome on food intake, body weight and morbidity [19]. Other studies have reported that a high dose of 400mg daily L-theanine is safe, tolerable and effective [25]. In addition, a 200-400mg dose of L-theanine reported a decrease in anxiety and stress in healthy participants [30]. Interestingly, a study assessing the effect of L-theanine on tumour proliferation and growth in mice, found that a very high dose of between 12.5-25 times the recommended dietary allowance (RDA) of L-theanine decreased tumour growth by 36% [33].

Side effects

Theanine is considered non-toxic for humans and animals [19]. Regarding the safety of L-theanine, results of acute and toxicity have shown is safe even if a high dose is consumed [8]. Toxicological descriptions have also reported the absence of negative side effects in animal studies investigating L-theanine [10]. Currently, no indications have been made that a high dose of L-theanine causes any major side effects in humans [1], however L-theanine has been regarded as completely safe to consume as part of one’s diet [8].


Research has consistently used L-theanine and caffeine in low, moderate and high doses. In this manner, it has been shown that 100mg L-theanine stacked with 50mg caffeine has positive outcomes on attention [15]. Stacking L-theanine with caffeine has shown to improve cognition and attention; and L-theanine and caffeine alone did not show such similar effects.


L-theanine is approved as generally regarded as safe (GRAS) by the Food and Drug Administration (FDA) [20]. It has been documented that taking high doses of L-theanine is safe [8], with the FDA stating and recommending that the daily intake with a diet should be around 628mg per person [8]. In addition, the FDA has suggested that the daily amount of L-theanine should not exceed 1200mg. Long-term use of L-theanine has yet to be adequately established. Overall, L-theanine, even when combined with caffeine has been approved as being safe for consumption.


 [1] Jackson Williams, Jane Kellett, Paul Daniel Roach, Andrew McKune, Duane Mellor, Jasckson Thomas and Nenad Naumovski, 2016. L-theanine as a Functional Food Additive: It Role in Disease Prevention and Health Promotion. Beverages, 2:13.

[2] Kenta Kimura, Makoto Ozeki, Lekh Raj Juneja, Hideki Ohira, 2007. L-Theanine reduces psychological and physiological stress responses. Biological Psychology, 74.

[3] Crystal F. Haskell, David O. Kennedy, Anthea L. Milne, Keith A. Wesnes, Andrew B. Scholey, 2008. The effects of L-theanine, caffeine and their combination on cognition and mood. Biological Psychology, 77.

[4] Akiko Higashiyama, Hla Hla Htay, Makoto Ozeki, Lekh R. Juneja, 2011. Effects of L-theanine on attention and reaction time response. Journal of Fucntional Foods, 3.

[5] Anna C Nobre, Anling Rao and Gail N Owen, 2008. L-theanine, a natural constituent in tea, and its effect on mental state. Asia Pacific Journal of Clinical Nutrition, 17.

[6] Quan V Vuong, Michael C Bowyer and Paul D Roach, 2011. L-Theanine: properties, synthesis and isolation from tea. Journal of Science Food Agriculture, 91.

[7] Tae Il Kim, Yong Kyung Lee, Sang Gi Park, Im Seop Choi, Jung Ok Ban, Hyoung Kook Park, Sang-Yoon Nam, Young Won Yun, Sang Bae Han, Ki Wan Oh, Jin Tae Hong, 2009. L-Theanine, an amino acid in green tea, attenuates β-amyloid-induced cognitive dysfunction and neurotoxicity: Reduction in oxidative damage and inactivation of ERK/p38 kinase and NF-κB pathways. Free radical Biology and Medicine, 47.

[8] Duygu Turkozu and Nevin Sanlier, 2017. L-theanine, unique amino acid of tea, and its metabolism, health effects and safety. Critical Reviews in Food Science and Nutrition, 57:8.

[9] Takami Kakuda, 2011. Neuroprotective effects of theanine and its preventative effects on cognitive dysfunction. Pharmacological Research, 64.

[10] Pradeep J. Nathan, Kristy Lu, M. Gray and C. Oliver, 2009. The Neuropharmacology of L-Theanine (N-Ethyl-L-Glutamine): A Possible Neuroprotective and Cognitive Enhancing Agent. Journal of Herbal Pharmacotherapy, 6:2.

[11] Anne L. Lardner, 2013. Neurobiological effects of the green tea constituent theanine and its potential role in the treatment of psychiatric and neurodegenerative disorders. Nutritional Neurosience.

[12] Lekh Raj Juneja, Djong-Chi Chu, Tsutomu Okubo, Yukiko Nagato and Hidehiko Yokogoshi, 1999. L-theanine – a unique amino acid of green tea and its relaxation effect in humans. Trends in Science and Technology, 10.

[13] T.P. Rao, M Ozeki and L.R. Juneja, 2007. Suntheanine: A pure and safe L-theanine dietary supplement for relaxation and stress relief. Nutraceuticals.

[14] Suzanne J.L. Einother, Vanessa E.G. Martens, Jane A. Rycroft, Eveline A. De Bruin, 2010. L-Theanine and caffeine improve task switching but not intersensory attention or subjective alertness. Appetite, 54.

[15] Gail N. Owen, Holly Parnell, Eveline A. De Bruin, Jane A. Rycroft, 2008. The combined effects of L-theanine and caffeine on cognitive performance and mood. Nutritional Neuroscience, 11:4.

[16] Simon P. Kelly, Manuel Gomez-Ramirez, Jennifer L. Montesi, and John J. Foxe, 2008. L-Theanine and Caffeine in Combination Affect Human Cognition as Evidenced by Oscillatory alpha-Band Activity and Attention Task Performance. Journal of Nutrition, 138.

[17] T. Giesbrecht, J.A. Rycroft, M.J Rowson, E.A. De Bruin, 2010. The combination of L-theanine and caffeine improves cognitive performance and increases subjective alertness. Nutritional Neuroscience, 13:6.

[18] Chanaka N. Kahathuduwa, Tharaka L. Dassanayake, A.M. Tissa Amarakoon and Vajira S. Weerasinghe, 2016. Acute effects of theanine, caffeine and theanine-caffeine combination on attention. Nutritional Neuroscience, 20:6.

[19] Yue-Rong Liang, Chang Liu, Li-Ping Xiang and Xin-Qiang Zheng, 2015. Health Benefits of Theanine in Green Tea: A Review. Tropical Journal of Pharmaceutical Research, 14:10.

[20] Wanmeng Mu, Tao Zhang, Bo Jiang, 2015. An overview of biological production of L-theanine. Biotechnology Advances, 33.

[21] Janet Bryan, 2007. Psychological effects of dietary components of tea: caffeine and L-theanine. Nutrition Reviews, 66:2.

[22] Kathleen A. Head, and Gregory S. Kelly, 2009. Nutrients and Botanicals for Treatment of Stress: Adrenal Fatigue, Neurotransmitter Imbalance, Anxiety, and Restless Sleep. Alternative Medicine Review, 14:2.

[23] Cui Yin, Lingshan Gou, Yi Liu, Xiaoxing Yin, Ling Zhang, Genguang Jia and Xuemei Zhuang, 2011. Antidepressant-like Effects of L-theanine in the Forced Swim and Tail Suspension Tests in Mice. Phytotherapy Research, 25.

[24] Shinsuke Hidese, Miho Ota, Chisato Wakabayashi, Takamasa Noda, Hayato Ozawa, Tsutomu Okubo and Hiroshi Kunugi, 2017. Effects of chronic L-theanine administration in patients with major depressive disorder: an open-label study. Acta Neuropsychiatrica, 29.

[25] Michael R. Lyon, Mahendra P. Kapoor, Lekh R. Juneja, 2011. The Effects of L-Theanine (Suntheanine) on Objective Sleep Quality in Boys with Attention Deficit Hyperactivity Disorder (ADHD): A Randomised, Double-blind, Placebo-controlled Clinical Trial. Alternative Medicine Review, 16:4.

[26] Miho Ota, Chisato Wakabayashi, Noriko Sato, Hiroaki Hori, Kotaro Hattori, Toshiya Teraishi, Hayato Ozawa, Tsutomu Okubo and Hiroshi Kunugi, 2015. Effect of L-theanine on glutamatergic function in patients with schizophrenia. Acta Neuropsychiatrica, 27.

[27] Jessica R. Barrett, Derek K. Tracy, and Giovanni Giaroli, 2013. To Sleep or Not to Sleep: A Systematic Review of the Literature of Pharmacological Treatments of Insomnia in Children and Adolescents with Attention-Deficit/Hyperactivity Disorder. Journal of Child and Adolescent Psychopharmacology, 23:10.

[28] Ai Yoto, Mao Motoki, Satu Murao and Hidehiko Yokogoshi, 2012. Effects of L-theanine or caffeine intake on changes in blood pressure under physical and psychological stresses. Journal of Physiological Anthropology, 31:28.

Ana R. Nunes, Marco G. Alves, Paula I. Moreira, Pedro F. Oliveira and Branca M. Silva, 2015. Impact of Green Tea Consumption in Diabetes Mellitus-Induced Neurodegeneration.

[29] Alternative Therapies, 2006. Pharmacology and therapeutic uses of theanine. American Journal of Health System Pharmacology, 63.

[30] Lisa Scheid, Sabine Ellinger, Birgit Altehekd, Hannes Herholz, Jorg Ellinger, Thomas Henn, Hans-Peter Helfrich and Peter Stehle, 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.

[31] Ana R. Nunes, Marco G. Alves, Paula I. Moreira, Pedro F. Oliveira and Branca M. Silva, 2015. Impact of Green Tea Consumption in Diabetes Mellitus-Induced Neurodegeneration.

[32] Emma K. Keenan, Mike D.A. Finnie, Paul S. Jones, Peter J. Rogers, Caroline M. Priestley, 2011. How much theanine in a cup of tea? Effects of tea type and method of preparation. Food Chemistry, 125.

[33] BegonÄa ComõÂn-Anduix, Joan Boren, Sonia Martinez, Cristina Moro, Josep J. Centelles,
Raisa Trebukhina, Nataly Petushok, Wai-Nang Paul Lee, Laszlo G. Boros and Marta Cascante, 2001. The effect of theanine supplementation on tumour proliferation. European Journal of Biochemistry, 268.

Also known as:Theanine, 5-N-Ethyl-Glutamine
Good for: , , , , , , ,
Stacks well with: Coming soon…
Typical dose:100-200 mg
Half Life :2.5 - 4.5 Hours