The AtlasAmino acidsAromatic

TryptophanTrp · W

The rarest amino acid in protein and the largest of the twenty, the source of serotonin and melatonin, and most of all the source of NAD.

Status Reference · not yet an episodeSources 32Reviewed October 2026

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Skeletal formula — every corner and every line end is a carbon, and the hydrogens on carbon are left implied.

Molecule · Trp · 15 heavy atoms

Tryptophan

C₁₁H₁₂N₂O₂204.23 g/mol

The rarest amino acid in protein and the largest of the twenty, the source of serotonin and melatonin, and most of all the source of NAD.

Built fromthe charted ones open their own entry

C11CarbonH12Hydrogen N2Nitrogen O2Oxygen

Codes: Trp · W
Formula: C₁₁H₁₂N₂O₂
Molar mass: 204.23 g/mol
Systematic name: (2S)-2-amino-3-(1H-indol-3-yl)propanoic acid
Side chain: Indol-3-ylmethyl: a benzene ring fused to a pyrrole; the largest standard side chain, aromatic and mostly nonpolar.
Class: Aromatic
In the diet: Essential
Carbon skeleton: Glucogenic and ketogenic
pKa: α-COOH 2.38 · α-NH₃⁺ 9.39
Isoelectric point: pH 5.89
Hydropathy: -0.9 (Kyte–Doolittle)
Codons: UGG
Main transporters: SLC7A5 (LAT1, with CD98), SLC6A19 (B0AT1)

pKa and isoelectric point: Nelson and Cox, Lehninger Principles of Biochemistry, table of amino acid properties (free amino acid, 25 °C). Hydropathy: Kyte and Doolittle, J Mol Biol 1982. Essentiality: Reeds, J Nutr 2000. Formula and mass computed from the structure.

In brief

What it is

The largest of the twenty standard amino acids, with a two-ring indole side chain; it is also the least abundant in cells and one of the rarest in proteins ¹. It is essential, so it must come from food ².

Why it matters

It is the only source of serotonin and, from serotonin, of melatonin ^3,4. But most tryptophan, about 95% of what is broken down, goes the other way, down the kynurenine pathway, which makes NAD⁺ and can substitute for niacin in the diet ^5,6.

Where it runs short

Too little tryptophan and niacin together causes pellagra: dermatitis, diarrhoea, dementia and, untreated, death; in Hartnup disorder poor tryptophan absorption can do the same on a normal diet ^7,8.

Where it turns

Tryptophan itself is not very toxic, but in 1989 a contaminated tryptophan supplement caused an epidemic of eosinophilia–myalgia syndrome in the United States ^9,10.

The serotonin story is the famous one. The NAD story is the big one.

The molecule

Tryptophan’s side chain is indole, a benzene ring fused to a five-membered ring containing nitrogen. It is the largest of the twenty standard side chains ¹.

It is also the most expensive amino acid to build, with the most complex and energy-consuming synthesis, and the least abundant free amino acid in cells; it is one of the rarest in the proteome ¹.

Charge · pHTryptophan carries almost no net charge at the pH of blood.

Move across the chart to read the charge at any pH.

Computed from its pKa values (α-carboxyl 2.38, α-amino 9.39) by the Henderson–Hasselbalch equation, for the free amino acid in water at 25 °C. Inside a folded protein the same groups can shift by a unit or more. The faint lines are the other amino acids.

HydropathyTryptophan scores -0.9: the 10th most water-loving of the twenty.

Kyte–Doolittle hydropathy index: positive values avoid water and tend to be buried inside a folded protein, negative values sit on its surface. Each letter is an amino acid; choose one to open it.

The genetic codeTryptophan has a single codon. A change to any one of its three letters writes a different amino acid, or a stop.

The 64 codons of the standard genetic code. Codons for tryptophan are marked.
1st ↓ 2nd →	U	C	A	G	3rd
U	UUUPhe	UCUSer	UAUTyr	UGUCys	U
	UUCPhe	UCCSer	UACTyr	UGCCys	C
	UUALeu	UCASer	UAAStop	UGAStop	A
	UUGLeu	UCGSer	UAGStop	UGGTrp	G
C	CUULeu	CCUPro	CAUHis	CGUArg	U
	CUCLeu	CCCPro	CACHis	CGCArg	C
	CUALeu	CCAPro	CAAGln	CGAArg	A
	CUGLeu	CCGPro	CAGGln	CGGArg	G
A	AUUIle	ACUThr	AAUAsn	AGUSer	U
	AUCIle	ACCThr	AACAsn	AGCSer	C
	AUAIle	ACAThr	AAALys	AGAArg	A
	AUGMet	ACGThr	AAGLys	AGGArg	G
G	GUUVal	GCUAla	GAUAsp	GGUGly	U
	GUCVal	GCCAla	GACAsp	GGCGly	C
	GUAVal	GCAAla	GAAGlu	GGAGly	A
	GUGVal	GCGAla	GAGGlu	GGGGly	G

Where it comes from

Animals cannot make the indole ring, so tryptophan is essential. The adult requirement is 4 mg per kilogram a day ²; a 2026 study in 23 adults over 60 found an average need of 3.9, with no difference between men and women or between people in their sixties and seventies ¹¹.

Tryptophan also counts towards niacin. About 60 mg of dietary tryptophan is generally taken to yield 1 mg of niacin, and a study in Japanese women estimated 67 ⁶; the ratio is not fixed and changes with how much niacin is already present ¹².

EssentialMust come from food. The adult requirement is 4 mg per kilogram a day; a 2026 tracer study in adults over 60 found 3.9 ^2,11.

How much

4 mg per kilogram a day for adults ^2,11.

Where it is in food

Any protein. Because 60 mg of tryptophan yields about 1 mg of niacin, a protein-rich diet also supplies niacin ⁶.

In the bottle · fermentedMade by fermentation in engineered bacteria through the shikimate pathway ¹³. Fermentation is also how the 1989 disaster happened: one manufacturer changed its bacterial strain and purification, and impurities in its product were linked to eosinophilia–myalgia syndrome ^9,10.

What the body does with it

The kynurenine pathway handles about 95% of tryptophan breakdown and makes NAD⁺, the electron carrier of every cell ⁵. Its first step is the control point: tryptophan 2,3-dioxygenase in the liver, induced by glucocorticoids and regulated by haem, and indoleamine 2,3-dioxygenase in other tissues, induced by interferon-γ ⁵.

Serotonin is made by tryptophan hydroxylase, the rate-limiting enzyme. TPH1 works in the enterochromaffin cells of the gut, which make almost all of the body’s peripheral serotonin; TPH2 works in the raphe neurons of the brain ^3,14. Serotonin does not readily cross the blood–brain barrier, so the gut’s serotonin and the brain’s are separate supplies ³.

In the pineal gland and elsewhere, serotonin is acetylated and then methylated to make melatonin ⁴.

Gut bacteria take a third route, turning tryptophan into indoles. One of them, indole-3-propionic acid, exists in mice only when gut bacteria are present ¹⁵; in people, higher levels go with a more diverse microbiome and a lower risk of developing type 2 diabetes ^16,17.

In three sentences each

Mostly to NAD, not to serotonin

About 95% of dietary tryptophan breakdown runs through the kynurenine pathway, 90% of it in the liver, ending in nicotinic acid and NAD⁺; serotonin takes only a small fraction ^5,18.

Two gates set the split

Tryptophan 2,3-dioxygenase in the liver is driven by glucocorticoids, and indoleamine 2,3-dioxygenase elsewhere is switched on by interferon-γ, so inflammation diverts tryptophan into kynurenine ^5,19.

A queue at the brain

Tryptophan crosses into the brain on a carrier it shares with the other large neutral amino acids, so its ratio to them, not its own level, sets brain serotonin synthesis; in rats a protein meal raised plasma tryptophan but not brain tryptophan ^20,21.

How it is made, moved and broken down

In carcinoid syndrome, a tumour turns large amounts of tryptophan into serotonin and so diverts it from NAD; ten of 36 such patients were biochemically niacin-deficient and one had pellagra ¹⁸.

Carbon skeleton · glucogenic and ketogenicClassed as both glucogenic and ketogenic, but its more important product is NAD⁺ ⁵.

To serotonin and melatoninTryptophan hydroxylase is rate-limiting ^3,4.

Tryptophan
Tryptophan hydroxylaseTPH1, TPH2 · BH4, iron
5-Hydroxytryptophan
Aromatic L-amino acid decarboxylaseDDC · vitamin B6
Serotonin
Arylalkylamine N-acetyltransferaseAANAT · acetyl-CoA
N-Acetylserotonin
Acetylserotonin O-methyltransferaseASMT · SAM
Melatonin

Down the kynurenine pathwayWhere most tryptophan goes, and how the body makes NAD⁺ from it ⁵.

Tryptophan
TDO (liver) or IDO (elsewhere)TDO2, IDO1 · haem, O₂
N-Formylkynurenine
FormamidaseAFMID
Kynurenine
Several stepsKMO, KYNU, HAAO, QPRT · vitamin B2, B6
Quinolinic acid → NAD⁺

In the gut, by bacteriaMicrobes make indoles that the host cannot ^15,22.

Tryptophan
Bacterial enzymes
Indole and indole-3-propionic acid

How it crosses membranes

SLC7A5 · LAT1, with CD98blood–brain barrier and placenta — shared with the other large neutral amino acids, which compete with tryptophan for entry to the brain ^20,21
SLC6A19 · B0AT1small intestine and kidney — absorbs tryptophan from food and reclaims it from urine; its loss causes Hartnup disorder ⁸

Where it matters most

Liver: Breaks down most tryptophan, by TDO, into kynurenine and on to NAD⁺ ⁵.
Gut: Enterochromaffin cells make almost all peripheral serotonin; gut bacteria make indoles of their own ^3,22.
Brain: Raphe neurons make serotonin with TPH2, from tryptophan that has competed its way across the blood–brain barrier ^3,20.
Immune cells and inflamed tissue: Interferon-γ induces IDO, which consumes tryptophan locally ^5,19.

When it goes wrong

Too little

Pellagra

Deficiency of niacin, of tryptophan, or both: the four Ds of dermatitis, diarrhoea, dementia and death. Causes today include alcohol, malabsorption and drugs such as isoniazid ⁷.

How it is foundA clinical diagnosis, confirmed by response to niacin ⁷.

Inherited

Hartnup disorder

SLC6A19 · autosomal recessive

Named for an English family described in 1956. The gut and kidney cannot transport neutral amino acids, so tryptophan is lost in the urine; some people develop pellagra-like rashes, unsteady gait and psychiatric symptoms ⁸.

How it is foundNeutral amino acids in the urine, and SLC6A19 sequencing ⁸.

Acquired

Carcinoid syndrome

Serotonin-secreting neuroendocrine tumours, most often of the small bowel, divert tryptophan into serotonin; niacin deficiency follows in some patients ¹⁸. 5-HIAA is the marker, and is most accurate for carcinoid heart disease ²³.

How it is foundUrine or plasma 5-HIAA ^23,24.

Drug

Eosinophilia–myalgia syndrome

The 1989 US epidemic linked to contaminated L-tryptophan from a single manufacturer ^9,25. A rat study reproduced some of its muscle-sheath changes with one contaminant, 1,1′-ethylidenebis(tryptophan) ²⁶.

How it is foundEosinophil count and clinical features, with a history of the supplement ⁹.

Drug

IDO inhibitors in cancer

IDO1

Tumours can use IDO to starve immune cells of tryptophan, so IDO inhibitors were tried with immunotherapy. In the phase 3 ECHO-301 trial in 706 people with melanoma, adding epacadostat to pembrolizumab changed neither progression-free nor overall survival ²⁷.

How it is foundNone in routine use.

How it is measured

Tryptophan’s products are measured more often than tryptophan itself. 5-HIAA follows serotonin-secreting tumours ²³; the kynurenine-to-tryptophan ratio follows immune activation in research ¹⁹; and niacin status, not tryptophan, is measured when pellagra is suspected ¹⁸.

5-HIAA, in urine or bloodThe main breakdown product of serotonin, measured to diagnose and follow serotonin-secreting neuroendocrine tumours ²³.In midgut neuroendocrine tumours, the 24-hour urine test discriminated with an area under the curve of 0.80, and plasma 0.72; in one comparison, serum at a 135 nmol/L cut-off had 91% sensitivity against urine ^23,24.Specificity was only about 62% in that comparison, and the test reflects tumour serotonin, not the serotonin of the brain ^3,24.
Kynurenine-to-tryptophan ratioA blood index of how fast IDO is breaking tryptophan down ¹⁹.Research.Tracks immune activation driven by interferon-γ ¹⁹.Not specific to any one disease; meaningful only alongside other immune markers ¹⁹.
Plasma tryptophanFree and total tryptophan in plasma; low in Hartnup disorder, where it is lost in the urine ⁸.A single plasma value does not say how much reaches the brain, which depends on the competing amino acids ²⁰.

Food, supplements and the evidence

Establishedreplicated in people, for a named outcome

Niacin, and dietary protein, prevent and treat pellagra ⁷.

Uncertainsmall, short, mixed, surrogate or preclinical

Tryptophan or 5-HTP for depression. A 2002 review found only two of 108 trials good enough to pool; a 2020 meta-analysis of 5-HTP found large effects from weak studies with few placebo groups ^28,29.
Indole-3-propionic acid as a marker or mediator of metabolic health; the associations are in observational cohorts ^16,17.

Sold asthe claim on the label, against the evidence

“Turkey (or warm milk) makes you sleepy because of the tryptophan.” A protein meal brings in the competing amino acids along with tryptophan, and in rats it raised blood tryptophan without raising brain tryptophan ²⁰.

What is strange about it

In 1989 an epidemic of eosinophilia–myalgia syndrome, with disabling muscle pain and very high eosinophil counts, was traced to tryptophan made by one Japanese company: 29 of 30 cases had taken its product, against 21 of 35 controls ⁹. Contaminants appeared after it changed its bacterial strain and cut the carbon used to purify the product ^9,10; in 2017 one of them, “peak AAA,” was still being structurally identified ²⁵.

Tryptophan supplements vanished from US shelves after the epidemic, and 5-HTP took their place ³⁰.

The serotonin theory of depression rests partly on tryptophan depletion studies. Pooled, they lowered mood in drug-free people who had recovered from depression, slightly in those with a family history, and not at all in healthy volunteers ^31,32.

Where it connects

In the Atlas

PhePhenylalanineAromatic TyrTyrosineAromatic HisHistidinePositively charged

Topics on the map

On the map

A star in Gut & microbiome, one of 8. Only a small fraction becomes serotonin; most runs down the kynurenine pathway.

Find it on the map

Sources

32 sources, numbered as they are cited. Every one was checked against PubMed or its publisher before it was cited here; the note under each says what it shows and what it does not.

1
Barik S. The uniqueness of tryptophan in biology: properties, metabolism, interactions and localization in proteins.Int J Mol Sci · 2020 · 21(22):8776doi:10.3390/ijms21228776 · PMID 33233627
Largest amino acid; most costly to make; least abundant.
2
Joint WHO/FAO/UNU Expert Consultation. Protein and amino acid requirements in human nutrition.World Health Organ Tech Rep Ser · 2007 · (935):1–265PMID 18330140
Tryptophan, 4 mg/kg/day.
3
Jones LA, Sun EW, Martin AM, Keating DJ. The ever-changing roles of serotonin.Int J Biochem Cell Biol · 2020 · 125:105776doi:10.1016/j.biocel.2020.105776 · PMID 32479926
TPH1 in gut, TPH2 in brain; peripheral serotonin from enterochromaffin cells.
4
Tan DX, Hardeland R, Back K, et al. On the significance of an alternate pathway of melatonin synthesis via 5-methoxytryptamine: comparisons across species.J Pineal Res · 2016 · 61(1):27–40doi:10.1111/jpi.12336 · PMID 27112772
The classic pathway, serotonin to N-acetylserotonin to melatonin.
5
Badawy AA. Kynurenine pathway of tryptophan metabolism: regulatory and functional aspects.Int J Tryptophan Res · 2017 · 10:1178646917691938doi:10.1177/1178646917691938 · PMID 28469468
About 95% of tryptophan breakdown; TDO and IDO; NAD⁺.
6
Fukuwatari T, Ohta M, et al. Conversion ratio of tryptophan to niacin in Japanese women fed a purified diet conforming to the Japanese Dietary Reference Intakes.J Nutr Sci Vitaminol (Tokyo) · 2004 · 50(6):385–391doi:10.3177/jnsv.50.385 · PMID 15895512
Ten women; about 67 mg tryptophan per mg niacin, against the usual 60.
7
Prabhu D, Dawe RS, Mponda K. Pellagra a review exploring causes and mechanisms, including isoniazid-induced pellagra.Photodermatol Photoimmunol Photomed · 2021 · 37(2):99–104doi:10.1111/phpp.12659 · PMID 33471377
Causes and features of pellagra.
8
Kleta R, Romeo E, Ristic Z, et al. Mutations in SLC6A19, encoding B0AT1, cause Hartnup disorder.Nat Genet · 2004 · 36(9):999–1002doi:10.1038/ng1405 · PMID 15286787
The Hartnup gene.
9
Belongia EA, Hedberg CW, Gleich GJ, et al. An investigation of the cause of the eosinophilia-myalgia syndrome associated with tryptophan use.N Engl J Med · 1990 · 323(6):357–365doi:10.1056/NEJM199008093230601 · PMID 2370887
29 of 30 cases against 21 of 35 controls used one company’s product.
10
Mayeno AN, Gleich GJ. Eosinophilia-myalgia syndrome and tryptophan production: a cautionary tale.Trends Biotechnol · 1994 · 12(9):346–352doi:10.1016/0167-7799(94)90035-3 · PMID 7765187
How a manufacturing change introduced the impurities.
11
Wang Z, Tomlinson C, Pencharz P, et al. Dietary tryptophan requirements in adults aged >60 years is not affected by sex or decades of age.J Nutr · 2026 · 156(11):101827doi:10.1016/j.tjnut.2026.101827 · PMID 42727854
23 older adults; 3.9 mg/kg/day pooled.
12
Fukuwatari T, Shibata K. Effect of nicotinamide administration on the tryptophan-nicotinamide pathway in humans.Int J Vitam Nutr Res · 2007 · 77(4):255–262doi:10.1024/0300-9831.77.4.255 · PMID 18271280
The conversion ratio changes with niacin intake.
13
Hirasawa T, Satoh Y, Koma D. Production of aromatic amino acids and their derivatives by Escherichia coli and Corynebacterium glutamicum.World J Microbiol Biotechnol · 2025 · 41(2):65doi:10.1007/s11274-025-04264-3 · PMID 39915353
Fermentation through the shikimate pathway.
14
Walther DJ, Peter JU, Bashammakh S, et al. Synthesis of serotonin by a second tryptophan hydroxylase isoform.Science · 2003 · 299(5603):76doi:10.1126/science.1078197 · PMID 12511643
The discovery of TPH2.
15
Wikoff WR, Anfora AT, Liu J, et al. Metabolomics analysis reveals large effects of gut microflora on mammalian blood metabolites.Proc Natl Acad Sci U S A · 2009 · 106(10):3698–3703doi:10.1073/pnas.0812874106 · PMID 19234110
Mice: indole-3-propionic acid depends entirely on gut bacteria.
16
Menni C, Hernandez MM, Vital M, et al. Circulating levels of the anti-oxidant indoleproprionic acid are associated with higher gut microbiome diversity.Gut Microbes · 2019 · 10(6):688–695doi:10.1080/19490976.2019.1586038 · PMID 31030641
1,018 women; microbiome explained far more of IPA than diet or genes.
17
de Mello VD, Paananen J, Lindström J, et al. Indolepropionic acid and novel lipid metabolites are associated with a lower risk of type 2 diabetes in the Finnish Diabetes Prevention Study.Sci Rep · 2017 · 7:46337doi:10.1038/srep46337 · PMID 28397877
Observational; replicated in a Swedish cohort.
18
Shah GM, Shah RG, Veillette H, et al. Biochemical assessment of niacin deficiency among carcinoid cancer patients.Am J Gastroenterol · 2005 · 100(10):2307–2314doi:10.1111/j.1572-0241.2005.00268.x · PMID 16181385
Serotonin is normally a small fraction of tryptophan use; 10 of 36 carcinoid patients niacin-deficient.
19
Strasser B, Becker K, Fuchs D, Gostner JM. Kynurenine pathway metabolism and immune activation: peripheral measurements in psychiatric and co-morbid conditions.Neuropharmacology · 2017 · 112(Pt B):286–296doi:10.1016/j.neuropharm.2016.02.030 · PMID 26924709
The kynurenine-to-tryptophan ratio as an IDO index.
20
Fernstrom JD, Wurtman RJ. Brain serotonin content: physiological regulation by plasma neutral amino acids.Science · 1972 · 178(4059):414–416doi:10.1126/science.178.4059.414 · PMID 5077329
Rats: the ratio of tryptophan to competing amino acids sets brain tryptophan.
21
Scalise M, Galluccio M, Console L, et al. The human SLC7A5 (LAT1): the intriguing histidine/large neutral amino acid transporter and its relevance to human health.Front Chem · 2018 · 6:243doi:10.3389/fchem.2018.00243 · PMID 29988369
LAT1 at the blood–brain barrier.
22
Agus A, Planchais J, Sokol H. Gut microbiota regulation of tryptophan metabolism in health and disease.Cell Host Microbe · 2018 · 23(6):716–724doi:10.1016/j.chom.2018.05.003 · PMID 29902437
Serotonin, kynurenine and indole pathways under microbial control.
23
de Mestier L, Savagner F, Brixi H, et al. Plasmatic and urinary 5-hydroxyindolacetic acid measurements in patients with midgut neuroendocrine tumors: a GTE study.J Clin Endocrinol Metab · 2021 · 106(4):e1673–e1682doi:10.1210/clinem/dgaa924 · PMID 33382891
80 tumours, 17 controls; AUROC 0.80 urine, 0.72 plasma.
24
Ewang-Emukowhate M, Subramaniam K, Lam F, et al. Plasma or serum 5-hydroxyindoleacetic acid can be used interchangeably in patients with neuroendocrine tumours.Scand J Clin Lab Invest · 2023 · 83(8):576–581doi:10.1080/00365513.2023.2286645 · PMID 38112030
135 nmol/L cut-off: sensitivity 91%, specificity 62% against urine.
25
Klarskov K, Gagnon H, Boudreault PL, et al. Structure determination of disease associated peak AAA from L-tryptophan implicated in the eosinophilia-myalgia syndrome.Toxicol Lett · 2017 · 282:71–80doi:10.1016/j.toxlet.2017.10.012 · PMID 29037509
The one contaminant statistically linked to cases.
26
Emslie-Smith AM, Mayeno AN, Nakano S, et al. 1,1′-Ethylidenebis[tryptophan] induces pathologic alterations in muscle similar to those observed in the eosinophilia-myalgia syndrome.Neurology · 1994 · 44(12):2390–2392doi:10.1212/wnl.44.12.2390 · PMID 7991132
Rats; small animal study.
27
Long GV, Dummer R, Hamid O, et al. Epacadostat plus pembrolizumab versus placebo plus pembrolizumab in patients with unresectable or metastatic melanoma (ECHO-301/KEYNOTE-252): a phase 3, randomised, double-blind study.Lancet Oncol · 2019 · 20(8):1083–1097doi:10.1016/S1470-2045(19)30274-8 · PMID 31221619
706 patients; progression-free survival hazard ratio 1.00.
28
Shaw K, Turner J, Del Mar C. Are tryptophan and 5-hydroxytryptophan effective treatments for depression? A meta-analysis.Aust N Z J Psychiatry · 2002 · 36(4):488–491doi:10.1046/j.1440-1614.2002.01046.x · PMID 12169147
Two of 108 trials met quality criteria.
29
Javelle F, Lampit A, Bloch W, et al. Effects of 5-hydroxytryptophan on distinct types of depression: a systematic review and meta-analysis.Nutr Rev · 2020 · 78(1):77–88doi:10.1093/nutrit/nuz039 · PMID 31504850
13 studies; weak designs, high heterogeneity.
30
Preuss HG, Echard B, Talpur N, et al. Does 5-hydroxytryptophan cause acute and chronic toxic perturbations in rats?Toxicol Mech Methods · 2006 · 16(5):281–286doi:10.1080/15376520500195616 · PMID 20021026
Tryptophan withdrawn and replaced by 5-HTP on the market; rat toxicity study.
31
Ruhé HG, Mason NS, Schene AH. Mood is indirectly related to serotonin, norepinephrine and dopamine levels in humans: a meta-analysis of monoamine depletion studies.Mol Psychiatry · 2007 · 12(4):331–359doi:10.1038/sj.mp.4001949 · PMID 17389902
Tryptophan depletion lowers mood only in vulnerable groups.
32
Moncrieff J, Cooper RE, Stockmann T, et al. The serotonin theory of depression: a systematic umbrella review of the evidence.Mol Psychiatry · 2023 · 28(8):3243–3256doi:10.1038/s41380-022-01661-0 · PMID 35854107
Depletion had no effect in 566 healthy volunteers. Contested.

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