L-Theanine: History and Discovery
People had been drinking tea for the better part of two thousand years before anyone knew what made a fine cup of green tea taste savory and sweet rather than merely bitter. The answer turned out to be a single, unusual amino acid. In 1949 a Japanese chemist named Yajiro Sakato, working on the chemistry of the tea plant in Kyoto, identified a new compound in green tea leaves; he published its description in 1950 and named it theanine, after the old scientific name for tea. This article tells that story plainly: what Sakato actually found and how he named it, how British chemists confirmed the discovery a few years later, why the leaf makes so much of this one molecule, and how a quiet finding in a tea laboratory eventually became one of the most studied calming compounds in the world. Where the record is firm we say so; where a detail is reported rather than fully documented, we flag it.
Table of Contents
- Tea Before Its Chemistry Was Known
- The Discovery: Yajiro Sakato, 1949–1950
- Where the Name “Theanine” Comes From
- Confirmation in England: Cartwright, Roberts & Wood, 1954
- Why the Tea Plant Makes So Much of It
- From Laboratory to Pantry: Food Approval and Suntheanine
- The Modern Era: Brain Science and the Calm-Alert Molecule
- Research Papers and References
- Connections
- Featured Videos
Tea Before Its Chemistry Was Known
Tea — the leaf of the evergreen shrub Camellia sinensis — has been cultivated and drunk in East Asia for well over a thousand years, prized for a taste that good green tea drinkers describe as umami: a rounded, savory, almost broth-like sweetness quite different from the flat bitterness of a badly made cup. For most of that long history nobody could say what was responsible for that quality. Tea was understood through taste, ritual, and tradition, not through chemistry.
That began to change only in the modern era, as chemists learned to take plants apart molecule by molecule. By the first half of the twentieth century the broad outlines of tea's chemistry were coming into view: caffeine had long been known, and the bitter, astringent catechins (the polyphenols now famous as green-tea antioxidants) and tannins were being studied. But the source of green tea's distinctive savory-sweet note remained unexplained. The compound responsible was present in quantity, yet it had never been named, because it is almost unique to tea and barely occurs elsewhere in the plant or animal world. Finding it required someone to look closely at the free amino acids of the leaf — which is exactly what happened in Japan at the end of the 1940s.
The Discovery: Yajiro Sakato, 1949–1950
The discovery of theanine is unusually well attributed for a natural product: it has a single named discoverer, a date, and a primary publication. The chemist Yajiro Sakato, working in Kyoto, Japan on the chemical constituents of tea, identified the new compound in green tea leaves in 1949. He set out his findings in a paper titled “Studies on the Chemical Constituents of Tea,” published in 1950 in the Journal of the Agricultural Chemical Society of Japan (in Japanese, Nippon Nogei Kagaku Kaishi). It is in that work that the compound is described and given the name theanine.
What Sakato had isolated was a free amino acid — that is, one floating loose in the leaf rather than locked into a protein. Chemically he characterized it as N-ethyl-L-glutamine, also written as L-γ-glutamylethylamide (gamma-glutamylethylamide). In plain terms, the molecule is a close cousin of two of the body's most important amino acids: it is glutamine, or the related glutamate, with a small ethyl group attached. That family resemblance is not a footnote — it is the key to almost everything theanine does in the brain, because the molecule is shaped enough like glutamate to slip across the same gates and touch the same receptors. The chemistry discovered in a Kyoto tea laboratory in 1949 is, decades later, the reason a 200 mg capsule produces a measurable shift in brain rhythms.
It is worth being precise about the dates, because different sources give either 1949 or 1950 for “the discovery.” Both are right, describing two stages of the same event: Sakato identified and announced the new amino acid in 1949, and the formal scientific description was published in 1950. The compound was obtained from green tea leaves, and accounts specifically point to gyokuro — a premium shade-grown Japanese green tea that, as the later sections explain, happens to be exceptionally rich in this very molecule, which made it an ideal starting material from which to isolate enough of the substance to study.
Where the Name “Theanine” Comes From
The name theanine is a small piece of botanical history in itself. It is reported to derive from Thea — the old genus name for the tea plant — with the “-ine” ending conventional for amines and alkaloid-like compounds (the same ending found in caffeine and many other plant nitrogen compounds). In other words, theanine is simply “the tea substance.”
That older name has its own documented past. When Carl Linnaeus laid down the modern system of botanical naming in his Species Plantarum of 1753, he placed the tea plant in a genus he called Thea, giving the species the name Thea sinensis — literally “Chinese tea.” Later botanists merged Thea into the larger genus Camellia, and the tea plant's accepted scientific name became Camellia sinensis, which it remains today. By the time Sakato was working, Thea was the familiar historical name for tea, and it is the root preserved in the word theanine — a naming choice that ties the molecule permanently to the single plant that makes it. (We present this etymology as the standard reported derivation; the underlying botanical facts — Linnaeus's 1753 Thea sinensis and its later transfer to Camellia — are well documented.)
The naming is fitting because theanine really is, to a first approximation, tea's own amino acid. It is found in significant amounts almost nowhere else in nature: in the tea plant (Camellia sinensis) and in a small number of related Camellia species, in a single mushroom (Imleria badia, formerly Boletus badius, the bay bolete), and in the South American holly Ilex guayusa, a relative of yerba mate. For the human diet, though, the realistic source has always been tea. A compound that is essentially confined to one beverage plant is a natural candidate to be named after it.
Confirmation in England: Cartwright, Roberts & Wood, 1954
A discovery in science gains weight when other laboratories, working separately, find the same thing. That is exactly what happened with theanine. A few years after Sakato's publication, researchers in England studying the chemistry of tea independently described the same compound. In 1954, R. A. Cartwright, E. A. H. Roberts, and D. J. Wood published a paper plainly titled “Theanine, an amino-acid n-ethyl amide present in tea” in the Journal of the Science of Food and Agriculture. The title alone confirms the essentials of Sakato's finding: the substance is an amino acid, it carries the characteristic ethyl-amide group, and it is present in tea.
This English work mattered for two reasons. First, it corroborated, from a separate research tradition, that tea contains this distinctive amino acid — the kind of independent confirmation that turns a single report into established fact. Second, the team behind it sat at the center of mid-century tea chemistry: E. A. H. Roberts in particular was a leading figure in working out the polyphenols and other constituents of tea during exactly this period. Their attention helped move theanine from a Japanese discovery into the shared international literature on what tea is made of.
Between Sakato's isolation around 1949–1950 and this 1954 confirmation, then, theanine passed the basic test of a real discovery: found, named, published, and reproduced. Everything that came afterward — the food-industry uses, the brain research, the supplement on the shelf — rests on that foundation.
Why the Tea Plant Makes So Much of It
One reason theanine was discoverable at all is that the tea plant produces it in genuinely large amounts. Theanine is the dominant free amino acid in tea, commonly cited as accounting for roughly half of all the free amino acids in the leaf and on the order of 1–2% of the dry weight of green tea. For a single specialized compound, that is a remarkable share — the plant is, in effect, investing heavily in making it.
The biology behind that investment is now reasonably well understood. Theanine is synthesized chiefly in the roots of the tea plant, built from glutamate (or glutamic acid) joined to ethylamine, and is then transported up into the new shoots and young leaves — which is why the tender top leaves used for the best teas are the richest in it. Theanine also functions as a way for the plant to store and move nitrogen, a precious nutrient, around its tissues.
This biology explains a fact every serious tea drinker knows by taste, even without the chemistry. Growers of premium Japanese green teas such as gyokuro and matcha deliberately shade the plants for weeks before harvest. Shading slows photosynthesis and, crucially, keeps the plant from converting as much theanine into the bitter catechins that bright sunlight drives it to make. The leaves accordingly retain more theanine, and the resulting tea tastes sweeter, rounder, and more savory — higher in umami, lower in harshness. It is no accident that Sakato's discovery is associated with gyokuro: the shade-grown leaf is nature's most concentrated ordinary source of the molecule, the obvious material from which to first pull it out and study it.
From Laboratory to Pantry: Food Approval and Suntheanine
For its first years theanine was a laboratory curiosity — an interesting constituent of a familiar drink. Its move into everyday products came through the food industry. In 1964, Japan approved theanine for use in foods (with the customary exception of products intended for infants), recognizing it as a flavor-related constituent native to tea. In the United States, theanine has been treated as Generally Recognized as Safe (GRAS), with the U.S. Food and Drug Administration regarding it as safe at the serving levels used in supplements and foods. These regulatory steps reflect a simple underlying point: theanine is not a synthetic novelty but a substance people have consumed in tea for as long as tea has been drunk.
The other development that shaped theanine's modern life was manufacturing. Rather than extract the amino acid laboriously from mountains of tea leaves, producers learned to make pure L-theanine by fermentation and enzymatic methods, yielding a consistent, pharmaceutical-grade product. The best-known branded form is Suntheanine (Taiyo Corporation, Japan), a pure L-isomer preparation that became the material used in the majority of clinical trials. The distinction matters: the natural, biologically active form is specifically L-theanine, and a defined, single-isomer product is what allowed researchers to test precise doses and report reproducible results — the bridge between a compound found in a leaf and a compound studied in a clinic.
The Modern Era: Brain Science and the Calm-Alert Molecule
For several decades after its discovery, theanine was known mainly to food chemists and tea scientists as the source of green tea's savory taste. Its second life — as one of the world's most popular natural calming compounds — began when researchers turned from how it tastes to what it does in the brain. The pivotal observation, developed in studies from the late twentieth century onward, was that an oral dose of L-theanine produces a measurable increase in alpha brain waves — the electrical rhythm of relaxed, wakeful alertness — without causing drowsiness. Here at last was a chemical explanation for something tea drinkers had described for centuries: the sense of being calm and clear-headed at the same time.
From that finding the modern research literature grew quickly, and it grew in a particular direction. Because theanine is built like glutamate and glutamine, scientists found it could cross into the brain and gently modulate the very systems that govern arousal and anxiety — nudging the excitatory glutamate signal down, supporting the calming neurotransmitter GABA, and influencing dopamine and serotonin. The result is the now well-characterized “relaxed but alert” profile: a reduction in stress and anxiety that does not come with the sedation, impairment, or dependence of conventional tranquilizers. Reviews of this work, such as Lardner's 2014 survey of theanine's neurobiology and the comprehensive 2017 review by Türközü and Şanlıer, gather the accumulating evidence on its metabolism, effects, and safety.
The arc of theanine's history is therefore a satisfying one. A traditional beverage held a secret in its taste; a chemist in Kyoto named that secret in 1949; English chemists confirmed it in 1954; the food industry adopted it; and brain scientists, decades on, explained why a quiet cup of green tea has always felt the way it does. The clinical detail — mechanisms, doses, the caffeine pairing, the trials, and the cautions — is covered on the main L-Theanine page; this history is concerned with how the molecule came to be known in the first place. The honest closing note is the same one that fits any natural compound: a long record of safe use in tea is the reason to study theanine seriously, and modern research has largely rewarded that study — but understanding where it came from is part of using it wisely.
Research Papers and References
The list below combines the primary papers that established theanine with key modern reviews of its chemistry, biology, and effects. Sakato's 1950 paper is the original description of the compound; Cartwright, Roberts and Wood (1954) is the independent confirmation. Author names, titles, and journals are given as plain text; only the stable DOI, PMID, or archive link is hyperlinked, and each opens in a new tab.
- Sakato Y. Studies on the Chemical Constituents of Tea. Journal of the Agricultural Chemical Society of Japan (Nippon Nogei Kagaku Kaishi). 1950;23(6):262–267. (Original description and naming of theanine.) — doi:10.1271/nogeikagaku1924.23.262
- Cartwright RA, Roberts EAH, Wood DJ. Theanine, an amino-acid n-ethyl amide present in tea. Journal of the Science of Food and Agriculture. 1954;5(12):597–599. (Independent confirmation of theanine in tea.) — doi:10.1002/jsfa.2740051208
- Vuong QV, Bowyer MC, Roach PD. L-Theanine: properties, synthesis and isolation from tea. Journal of the Science of Food and Agriculture. 2011;91(11):1931–1939. — doi:10.1002/jsfa.4373 · PMID: 21735448
- Türközü D, Şanlıer N. L-theanine, unique amino acid of tea, and its metabolism, health effects, and safety. Critical Reviews in Food Science and Nutrition. 2017;57(8):1681–1687. — PMID: 26192072
- Lardner AL. Neurobiological effects of the green tea constituent theanine and its potential role in the treatment of psychiatric and neurodegenerative disorders. Nutritional Neuroscience. 2014;17(4):145–155. — PMID: 23883567
- Nobre AC, Rao A, Owen GN. L-theanine, a natural constituent in tea, and its effect on mental state. Asia Pacific Journal of Clinical Nutrition. 2008;17(S1):167–168. — PMID: 18296328
- 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 for Human Nutrition. 2020;75(1):12–23. — PMID: 31758301
- Theanine — history, discovery, and isolation from tea — PubMed: theanine history and isolation
- Theanine biosynthesis and accumulation in Camellia sinensis — PubMed: theanine biosynthesis in tea