Serotonin is a monoamine made from the amino acid tryptophan. Gut cells make most of the body's store. Platelets carry it in blood. The brain makes a smaller share for local use.

Serotonin
Serotonin
Abbreviation 5-HT
Molecular formula C₁₀H₁₂N₂O
Type Monoamine neurotransmitter/hormone
Administration N/A, doesn't cross blood-brain barrier; precursors like tryptophan/5-HTP used instead
Bioavailability N/A
Synonyms 5-hydroxytryptamine
Source Gut enterochromaffin cells (~90%), platelets, brainstem raphe nuclei
Ray's verdict Generally hurts
In the bioenergetic frame, excess serotonin is a stress and inflammation signal, not "happiness chemistry"

Drug marketing sold high serotonin as the chemistry of happiness. For Peat, excess serotonin is a stress and inflammation signal. It constricts vessels, impairs energy production, and helps lock in learned helplessness.[1]

In learned helplessness, the level of serotonin is high, and an excess of serotonin helps to create the state of learned helplessness.

— Ray Peat[2]

History

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Etymology

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The name combines Latin serum with "tonic," describing the substance's vasotonic effect: a factor found in blood serum that constricts blood vessels.

Maurice Rapport, Arda Green, and Irvine Page isolated and named serotonin in 1948, identifying it as the vasoconstrictor factor in clotted blood; it was later found to also act as a neurotransmitter in the brain and gut.

Serotonin was isolated and named in 1948 by Maurice Rapport, Arda Green, and Irvine Page, who found it in blood serum and identified it as the substance responsible for constricting blood vessels ("tonic" effect on vascular tone). Its name combines "sero-" (serum) and "tonin" (from that vessel-tightening, tonic action). It was independently isolated from intestinal tissue around the same period under the name "enteramine," before the two were shown to be the same molecule.

Structure/Chemical properties

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Serotonin (5-hydroxytryptamine, C₁₀H₁₂N₂O) is an indoleamine, built by adding a hydroxyl group to the amino acid tryptophan (via tryptophan hydroxylase) and then removing a carboxyl group (via aromatic amino acid decarboxylase). It does not cross the blood-brain barrier itself, so brain serotonin is synthesized locally from tryptophan that does cross, and is chemically and functionally separate from the much larger gut/platelet pool.

Function/Mechanism of Action

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Estrogen activates the pathway that turns tryptophan into serotonin. Progesterone does the opposite. High estrogen and low progesterone raise serotonin tone as one system, not as two unrelated lab values.[1]

Human genetics ties gut-derived serotonin directly to bone mass. People with a gain-of-function mutation in the bone-signaling co-receptor LRP5 have unusually high bone density along with a thickened jaw and palate, and their circulating serotonin runs low; people with loss-of-function LRP5 mutations develop osteoporosis and have elevated serotonin instead.[3] LRP5 acts, in part, by suppressing Tph1, the rate-limiting enzyme for serotonin synthesis in gut enterochromaffin cells of the duodenum; the serotonin that escapes this brake acts on osteoblasts through the Htr1b receptor to inhibit their proliferation, so more gut serotonin means less new bone.[4]

Two human skeletal dysplasias map to opposite shifts in gut serotonin synthesis; raising that pool lowers bone mass, and lowering it raises bone mass.[5] Oral LP533401, an inhibitor of tryptophan hydroxylase-1 that cuts gut-derived serotonin, prevented and treated osteoporosis in rodents after ovary removal for up to six weeks by raising bone formation alone, without a matching rise in resorption.[6]

Following the recognition that the SSRI drugs were causing osteoporosis, it was discovered that the serotonin produced in the intestine causes bone loss, and that inhibiting intestinal serotonin synthesis would stop bone loss and produce a bone building anabolic effect.

— Ray Peat[7]

Plasma serotonin precursors (including 5-HTP) and the metabolite 5-HIAA run higher in postmenopausal low-bone-mass and osteoporosis groups, and higher precursor/metabolite levels track with lower lumbar and femoral bone mineral density and higher turnover markers.[8] Oral 5-HTP aggravated periodontitis-driven alveolar bone loss in rats.[9] Dietary 5-HTP across pregnancy-to-lactation raised maternal bone calcium mobilization in rats,[10] and daily 5-HTP infusion before calving in dairy cows raised circulating serotonin and shifted calcium dynamics toward greater bone mobilization.[11]

Gut endotoxin and inflammation free platelet serotonin and amplify systemic effects. Hyperventilation raises serotonin and histamine as CO2 falls.[12] A high-tryptophan muscle-meat pattern without gelatin or other glycine-rich protein feeds the same pool. See Estrogen, Endotoxin, CO2, Gelatin.

Airborne ion charge also shifts brain serotonin. In mice held under controlled pollutant-free conditions, small negative air ions lowered brain serotonin within 12 hours of exposure, while positive ions raised it; the same polarity split showed up in blood serotonin measurements.[13] Natural settings with high negative-ion density, such as waterfalls and open water, are one proposed route by which time outdoors could lower serotonin tone independent of light or exercise. A controlled trial in 32 patients with chronic depression tested this directly: an hour of daily home exposure to high-density negative air ions produced a 51.1% improvement on the SIGH-SAD depression scale and a 50% remission rate over 5 weeks, matching bright light therapy (53.7% improvement, 50% remission) and far outperforming a low-density placebo ion generator (17.0% improvement, 0% remission).[14]

Depressed patients show evidence of disrupted blood-brain barrier integrity, including altered cerebrospinal-fluid/blood ratios of various molecules, and greater blood-brain barrier leakage in bipolar patients tracks with more severe depression.[15] Serotonin acting on the 5-HT4 receptor on brain microvascular endothelial cells increases blood-brain barrier permeability by downregulating the tight-junction protein occludin, one candidate mechanism for how elevated serotonin could open the barrier in depression.[16]

In mice on a high-fat diet, serotonin acting through HTR2B receptors on visceral fat cells drove lipolysis, and deleting or blocking the receptor protected against insulin resistance, fat-tissue inflammation, and fatty liver.[17] In bleomycin-injured mouse lungs, serotonin rose, and blocking 5-HT2A or 5-HT2B receptors reduced collagen deposition and fibrosis.[18]

Polyunsaturated fatty acids promote tryptophan uptake by the brain and its conversion to serotonin.[19] In female rats, perinatal omega-3 deficiency raised prefrontal serotonin turnover and lowered midbrain tryptophan hydroxylase-2 expression.[20]

The levers work together. Lower PUFA and endotoxin so the gut and liver are not constantly dumping inflammatory and serotonergic signals. Support thyroid and progesterone so estrogen-driven synthesis falls. Keep glucose and CO₂-retaining breathing so energy stays high enough to exit the helpless state. Use gelatin or other low-tryptophan protein to balance muscle meat. Coffee and aspirin appear in the same practical set as supports that reduce free serotonin impact and inflammatory tone.[1]

Carbon dioxide, high altitude, thyroid, progesterone, caffeine, aspirin, and decreased tryptophan consumption protect against excessive serotonin release. When sodium intake is restricted, there is a sharp increase in serotonin secretion.

— Ray Peat[21]

Low appetite in hypothyroid or inflammatory states blocks repair; cyproheptadine and progestogenic contexts appear in clinical and community discussion for raising appetite by blunting serotonin tone. Forcing large meals when nauseated fails; liquid calories help instead.

No single pill replaces that set. Cyproheptadine and other antiserotonin tools are advanced topics with their own risks. See Cyproheptadine, Thyroid, Progesterone, Coffee.

Avoiding prolonged fasting and stressful exercise that increase free fatty acids, and combining sugars with proteins to keep free fatty acids low, and using aspirin, niacinamide, or cyproheptadine to reduce the formation of free fatty acids by unavoidable stress, avoiding an excess of phosphate relative to calcium in the diet, having milk and other anti-stress foods at bedtime or during the night, and being in a brightly lighted environment during the day, with regular sunlight exposure, can minimize the harmful effects of excessive serotonin and reduce the inflammation, fibrosis, and atrophy associated with it.

— Ray Peat[22]

Hibernation, darkness, and schizophrenia

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Serotonin release drives the hibernation reaction: as an animal approaches hibernation and produces less CO2, the resulting serotonin release slows respiration, lowers temperature, suppresses appetite, and produces torpor.[23] Peat called serotonin "the torpor-hibernation chemical."[23] It "powerfully interferes with learning."[23]

I suspect that nocturnal sleep has the special function of minimizing the stress of darkness itself, and that it has subsidiary functions, including its now well confirmed role in the consolidation and organization of memory.

— Ray Peat[24]

Schizophrenia is one outcome of stress, both cumulative and acute.

— Ray Peat[25]

Prenatal stress commonly predisposes a person to develop schizophrenia at a later age.[23] See Schizophrenia for the fuller serotonin-versus-dopamine treatment picture, including why drugs that block serotonin (with or without also raising dopamine tone) relieve symptoms.

Clinical significance

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Vessels tighten. Oxidative metabolism falls. Mood can look like helpless depression rather than simple "low serotonin sadness." Gut motility swings. Fibrosis and inflammatory shock lines appear when serotonin stays high. Antiserotonin drugs show up in fibrosis and leak-related research for that reason.[1]

Serotonin's clinical footprint beyond mood includes migraine, carcinoid syndrome, dumping syndrome, vascular disease, and hypertension; that recognition drove decades of work on serotonin antagonists, with migraine prevention as the widest use.[26]

In rodent learned helplessness experiments, the precursors L-tryptophan and 5-HTP each impaired shuttle-box escape learning, and the serotonin antagonist methysergide blocked the 5-HTP effect and the deficit after prolonged inescapable shock.[27] In rats given escapable rather than inescapable shock, the ventral medial prefrontal cortex inhibits stress activation of the serotonergic dorsal raphe nucleus.[28]

Increasingly, intestinal serotonin is being recognized as a factor in osteoporosis, migraine, irritable bowel syndrome, appendicitis, and cancer.

— Ray Peat[29]

This is not advice to stop psychiatric serotonin drugs from a wiki page. Those drugs change receptor systems over time. Stopping them without medical care is dangerous. The page describes a metabolic reading of serotonin tone, not a deprescribing protocol. See Harm reduction, Serotonin syndrome.

Elevated transmission and rumination

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Serotonin transmission is elevated in multiple depressive phenotypes, including melancholia, a subtype associated with sustained cognition. The serotonergic system is framed as an evolved energy-regulation system rather than a simple mood elevator.[30] In depression, elevated serotonin supports processes that promote rumination; acute SSRI treatment exacerbates ruminative processes and worsens symptoms, while chronic treatment reverses rumination as compensatory responses restore energy homeostasis over weeks.[30] Learned helplessness in animal models is mediated by excess serotonin; overwhelming self-regulation can produce the same lock-in.[31]

Brain energy in animals

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Injecting rats with serotonin drops brain ATP and raises inorganic phosphate, while cytosolic phosphofructokinase (the rate-limiting glycolytic enzyme) becomes more active; lactate climbs at the same time, the same energetic signature seen in cerebral ischemia. Plasma hemoglobin also rose, reflecting red-cell lysis. The calmodulin antagonists trifluoperazine and thioridazine blocked all of these changes, pointing to a calmodulin-dependent step behind serotonin's acute hit to brain energy production.[32]

ME/CFS and central 5-HTergic hyperactivity

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Clinical PET observations behind the hyper-serotonergic hypothesis of ME/CFS report low binding potential for the 5-HT1A receptor or the serotonin transporter. In mice, high-dose fluoxetine produced dorsal-raphe serotonin spillover with ME/CFS-like fatigue, pain sensitivity, anxiety-like behavior, and HPA dysfunction; a 5-HT synthesis inhibitor reversed those fluoxetine-induced behaviors, and Htr1a knockdown reproduced fatigue, pain hypersensitivity, anxiety-like behavior, and lower plasma corticosterone.[33] Treat that as animal evidence for excess central serotonin tone in an ME/CFS-like model, not as proof that clinical SSRI doses cause human ME/CFS. See SSRIs.

Post-SSRI sexual dysfunction

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Raised synaptic serotonin from SSRIs commonly blunts genital sensation and sexual reward while the drug is taken. In an undetermined subset, genital numbness, pleasureless orgasm, loss of libido, and erectile dysfunction continue after the drug is stopped (Post-SSRI Sexual Dysfunction).[34][35] Candidate mechanisms such as 5-HT1A downregulation remain speculative.[36]

SSRI developmental neurotoxicity

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In pregnant women on SRIs, maternal platelet serotonin was about 88% lower and cord-blood infant platelet serotonin about 73% versus non-exposed pairs; lower values associated with more immature fetal movement quality.[37]

In a human iPSC-derived 3D brain organoid model, the SSRI paroxetine at therapeutic blood concentrations caused an 80% decrease in synaptic markers, a 60% decrease in neurite outgrowth, and a 40-75% decrease in oligodendrocyte populations -- an in-vitro developmental-neurotoxicity finding, not a direct human pregnancy outcome study, though prior epidemiological studies link prenatal SSRI exposure to autism risk.[38]

Acetylcholine and OCD models

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Cholinergic interneurons in the dorsal striatum directly trigger local serotonin release via nicotinic acetylcholine receptors on serotonergic axons, a coupling absent in the ventral striatum despite its denser serotonergic innervation. In Sapap3-knockout mice, a model of obsessive-compulsive-like behavior, this cholinergic system runs in overdrive, selectively amplifying serotonin release. Excess acetylcholine, rather than a primary serotonin deficit, may drive the compulsive phenotype.[39]

Gut serotonin and obesity

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TPH1, the rate-limiting enzyme for peripheral serotonin synthesis in the gut, runs about 40% higher in obese humans, and obesity increases peripheral serotonin more broadly. In mice, genetically deleting Tph1, or chemically inhibiting it with a small molecule, protects against diet-induced obesity, insulin resistance, and fatty liver while increasing energy expenditure, an effect that requires UCP1-mediated brown-fat thermogenesis; serotonin directly blunts the induction of that thermogenic program in brown and beige fat cells.[40]

Sensory gating

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Serotonin dampens rather than sharpens sensory throughput at the circuit level in at least two systems. In the olfactory bulb, serotonergic fibers activate periglomerular interneurons that release GABA to suppress transmitter release from olfactory sensory neurons, gating down odor signal before it reaches higher processing.[41] In the auditory cortex, "loudness dependence of auditory evoked potentials" (LDAEP) is used as an inverse marker of central serotonergic tone: rat electrophysiology combined with microdialysis found higher extracellular serotonin in primary auditory cortex tracked with a flatter, more dampened cortical response to increasing sound intensity, while a serotonin-lowering agent restored a steeper, more differentiated response curve.[42] Both findings support serotonin as a general damping signal on sensory circuits rather than establishing a broad claim across every sense.

Antidepressant withdrawal

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FAERS disproportionality work on drug withdrawal syndrome (2004–2023) placed antidepressants among the top positive-signal classes; paroxetine, duloxetine, and venlafaxine showed elevated reporting odds ratios (paroxetine ROR 29.36).[43] That metric is a spontaneous-report signal, not a serotonin-mechanism proof and not an incidence rate. Acute withdrawal reporting is not the same as Post-SSRI Sexual Dysfunction. See Drug withdrawal and SSRIs.

Opioid withdrawal

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The broad-spectrum serotonin antagonist mirtazapine relieved the full spectrum of opioid-withdrawal symptoms, including nausea, diarrhea, anxiety, and jitteriness. Excess serotonin, rather than serotonin loss, may drive much of the withdrawal syndrome.[44]

Aging brain

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In rats, regional brain serotonin stayed level from 2 to 30 months of age and rose at 36 months, while catecholamine levels fell progressively. A tryptophan-restricted diet from weaning to two years lowered serotonin in every brain region measured, and levels stayed below controls at 36 months after the rats returned to a normal diet (animal study).[45]

In old age, the amount of serotonin in the brain increases. This undoubtedly is closely related to the relative inability to turn off cortisol production that is characteristic of old age.

— Ray Peat[46]

Public perception

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The "happiness hormone" framing has displaced the older, more accurate stress/inflammation-signal view in public understanding. That framing's spread resembles the influence of corporate advertising and public relations on popular science writing.[47]

Serotonin syndrome

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Serotonin molecular structure
Serotonin molecular structure

Serotonin syndrome is acute toxicity from excess serotonergic activity. Standard toxicology links it to combining SSRIs with MAOIs, overdose, or multiple serotonergic drugs. Signs include agitation, hyperthermia, clonus, and autonomic instability.[48] Hunter Serotonin Toxicity Criteria classify severity from drug combinations and clinical signs; developed from over 2000 serotonergic-overdose admissions, they proved more sensitive (84% vs 75%) and more specific (97% vs 96%) than the older Sternbach criteria.[49]

Chronic serotonin elevation is a stress and inflammation signal; acute serotonin syndrome is the pharmacologic extreme of that chemistry.[50]

As a class, the serotonin antagonists have a very interesting place in pharmaceutical medicine, because the broad spectrum of their therapeutic activity suggests the great variety of problems caused by excess serotonin.

— Ray Peat[51]

By the end of the 1950s, it was widely accepted that migraine headaches and associated symptoms including nausea and visual disturbances were caused by an excess of serotonin, and antiserotonin drugs of various types were being used for treatment.

— Ray Peat[52]

Methylene blue is a monoamine oxidase inhibitor; combining it with SSRIs or other serotonergic drugs risks serotonin syndrome.[53] Standard emergency care may include Cyproheptadine (5-HT antagonist), benzodiazepines, and cooling.[48] Suspected cases need urgent medical care. See Serotonin, Methylene blue, Cyproheptadine, Harm reduction.

Branched-chain amino acids compete with tryptophan for cell entry and have mild anti-serotonin activity, relevant as an adjunct in serotonin-excess states.[54]

MDMA and amphetamine-type drugs

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MDMA-induced hyponatraemia was first described in 1993 and is life-threatening if untreated; women show higher incidence and increased odds of severe effects.[55] Serotonin and sympathomimetic toxicity after amphetamine-based drugs can cause severe morbidity and death. At one music festival, an on-site protocol of benzodiazepines, cold intravenous fluid, and rapid cooling treated 13 mild or moderate cases with 1 ambulance transfer (7.7%).[56] MDMA damages the brain through excess serotonin, and the good feeling reflects over-excitation rather than serotonin itself. At very low clinical doses it shows anti-depressant and anti-trauma effects tied to dopamine release and a drop in cortisol, and it is serotonergic like LSD only when abused at very high doses.[57] Call emergency services for high temperature, seizures, or confusion.

Tryptophan

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Tryptophan is an essential amino acid and precursor to Serotonin and melatonin. Mainstream psychiatry treats serotonin as a mood mediator; Peat read chronic serotonin elevation as a stress and inflammation signal.

In *Tryptophan, serotonin, and aging*, tryptophan is the only amino acid that is also carcinogenic in excess, and dietary tryptophan load strongly shapes stress responses and aging rate.[58]

Tryptophan, from dietary protein or from the catabolism of muscles, is turned into serotonin which activates the pituitary stress hormones, increasing cortisol, and intensifying catabolism, which releases more tryptophan.

— Ray Peat[59]

Serotonin, PUFA, and the stress loop

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Polyunsaturated fatty acids promote the absorption of tryptophan by the brain, and its conversion to serotonin.

— Ray Peat[60]

Stress liberates free fatty acids that increase brain tryptophan uptake and serotonin formation; serotonin raises ACTH and cortisol, perpetuating muscle catabolism and more tryptophan release.[61] Cysteine, methionine, and tryptophan suppress thyroid function together in studies Peat cited.[62]

In carcinoid syndrome, up to 60% of dietary tryptophan can convert to serotonin when a tumor bypasses hepatic clearance, producing flushing, diarrhea, anxiety, and right-heart valve disease in advanced cases.[63][64]

Epidemiological work tied the 1989–90 eosinophilia-myalgia syndrome outbreak in tryptophan users to a contaminant in the tablets. In rats, higher doses of tryptophan given for longer periods increased connective tissue and inflammatory cell proliferation in lung, spleen and gastrocnemius muscle (animal study).[65]

A carbohydrate-rich breakfast and a protein-rich breakfast had different effects on the blood ratio of tryptophan to its competing amino acids, and on the same ratio for tyrosine, the raw material for dopamine.[66]

Restriction, gelatin, and longevity

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Restricting only tryptophan, or only cysteine, produces a greater extension of the life span than achieved in most of the studies of caloric restriction.

— Ray Peat[67]

They kept the ability to reproduce up to the age of 36 months (versus 17 months for the rats on the usual diet), and both their average longevity and their maximum longevity increased significantly.

— Ray Peat[68]

The 36 and 17 month figures come from two different studies of Long-Evans female rats. In the 1976 study, no control rat older than 17 months produced a litter, while rats taken off a tryptophan-deficient diet produced litters at 17–28 months. Pair-fed controls, given the same amount of food with tryptophan added, showed many of the same effects, so this study cannot separate tryptophan restriction from eating less.[69] Weanling rats on severely tryptophan-deficient diets conceived and delivered as late as 36 months in a 1983 follow-up.[70] Rats returned to normal chow after 6–22 months of deficiency lived 36.3 ± 2.3 months on average against 30.5 ± 1.9 months for controls (8 and 14 rats).[71] On diets with 30% or 40% of control tryptophan from weaning, more rats died young and fewer died at late ages; histological aging was delayed in liver, heart, uterus, ovary, adrenal and spleen, with no delay in kidney, lung or aorta (rat study).[72]

Decreasing tryptophan or serotonin improves learning and alertness; increased serotonin impairs learning in the same article.[73]

Collagen makes up about half of an animal's protein and contains no tryptophan, so people who ate the whole animal, as head cheese, oxtails and chicken feet, got about half as much tryptophan relative to other amino acids.[74] Excess tryptophan can produce muscle pain, myositis and even muscular dystrophy, and gelatin helps correct those problems because it lacks tryptophan.[75]

A healthy person on a good diet can handle tryptophan, but estrogen lowers its conversion to niacin and sends it down the serotonin pathway.[76] When estrogen is relatively high, tryptophan becomes serotonin, slows the thyroid and lowers temperature; fruit with milk or cheese usually gives a good balance, and gelatin helps balance other proteins.[77]

Over-training, fibromyalgia, and practical balance

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"Over-training" fatigue may reflect tryptophan and serotonin overload from muscle protein catabolism.[78] Excessive serotonin interfering with muscle mitochondria may factor in fibromyalgia in evidence he cited.[79]

The injection of serotonin caused muscular dystrophy.

— Hans Selye (cited by Ray Peat)[80]

Balance muscle-meat tryptophan with Glycine/Gelatin; lower PUFA and gut Endotoxin. See Gut, Harm reduction.

References

[edit]
  1. ↑ 1.0 1.1 1.2 1.3 Ray Peat, "Serotonin, depression, and aggression," raypeat.com.
  2. ↑ Serotonin, depression, and aggression
  3. ↑ Boyden LM, Mao J, Belsky J, et al. "High Bone Density Due to a Mutation in LDL-Receptor-Related Protein 5," N Engl J Med. 2002;346(20):1513-1521. PMID 12015390.
  4. ↑ Yadav VK, Ryu JH, Suda N, et al. "Lrp5 Controls Bone Formation by Inhibiting Serotonin Synthesis in the Duodenum," Cell. 2008;135(5):825-837. PMID 19041748.
  5. ↑ Karsenty G, Yadav VK. "Regulation of bone mass by serotonin: molecular biology and therapeutic implications," Annu Rev Med. 2011;62:323-331. PMID 21073335.
  6. ↑ Yadav VK, Balaji S, Suresh PS, et al. "Pharmacological inhibition of gut-derived serotonin synthesis is a potential bone anabolic treatment for osteoporosis," Nat Med. 2010;16(3):308-312. PMID 20139991.
  7. ↑ Osteoporosis, aging, tissue renewal, and product science, raypeat.com
  8. ↑ Feng Q, Song X, Liu L, et al. "Plasma serotonin precursors and metabolite are correlated with bone mineral density and bone turnover markers in patients with postmenopausal osteoporosis," J Orthop Surg (Hong Kong). 2024;32(1). PMID 38613416.
  9. ↑ Li X, Wu X, Ma Y, et al. "Oral administration of 5-hydroxytryptophan aggravated periodontitis-induced alveolar bone loss in rats," Arch Oral Biol. 2015;60(5):740-747. PMID 25766472.
  10. ↑ Laporta J, Peters TL, Weaver SR, et al. "Feeding 5-hydroxy-l-tryptophan during the transition from pregnancy to lactation increases calcium mobilization from bone in rats," Domest Anim Endocrinol. 2013;44(4):184-192. PMID 23433710.
  11. ↑ Weaver SR, Prichard AP, Endres EL, et al. "Elevation of circulating serotonin improves calcium dynamics in the peripartum dairy cow," J Endocrinol. 2016;230(1):125-135. PMID 27390301.
  12. ↑ Ray Peat, "Leakiness, aging, and cancer," raypeat.com.
  13. ↑ Krueger AP, Kotaka S. "The effects of air ions on brain levels of serotonin in mice," Int J Biometeorol. 1969;13(1):25-38. PMID 5393639.
  14. ↑ Goel N, Terman M, Terman JS, Macchi MM, Stewart JW. "Controlled trial of bright light and negative air ions for chronic depression," Psychol Med. 2005;35(7):945-55. doi:10.1017/s0033291705005027. PMID 16045061.
  15. ↑ Medina-Rodriguez EM, Beurel E. "Blood brain barrier and inflammation in depression," Neurobiol Dis. 2022;175:105926. doi:10.1016/j.nbd.2022.105926. PMID 36375722.
  16. ↑ Becker G, Da Silva S, Sabo AN, et al. "Blood-Brain Barrier Permeability: Is 5-Hydroxytryptamine Receptor Type 4 a Game Changer?," Pharmaceutics. 2021;13(11):1856. doi:10.3390/pharmaceutics13111856. PMID 34834271.
  17. ↑ Choi WG, Choi W, Oh TJ, et al. "Inhibiting serotonin signaling through HTR2B in visceral adipose tissue improves obesity-related insulin resistance," J Clin Invest. 2021;131(23):e145331. doi:10.1172/JCI145331. PMID 34618686.
  18. ↑ Fabre A, Marchal-Sommé J, Marchand-Adam S, et al. "Modulation of bleomycin-induced lung fibrosis by serotonin receptor antagonists in mice," Eur Respir J. 2008;32(2):426-436. doi:10.1183/09031936.00126907. PMID 18321937.
  19. ↑ Ray Peat, "Serotonin: Effects in disease, aging and inflammation," raypeat.com.
  20. ↑ McNamara RK, Able J, Liu Y, et al. "Omega-3 fatty acid deficiency during perinatal development increases serotonin turnover in the prefrontal cortex and decreases midbrain tryptophan hydroxylase-2 expression in adult female rats: dissociation from estrogenic effects," J Psychiatr Res. 2009;43(6):656-663. doi:10.1016/j.jpsychires.2008.09.011. PMID 18986658.
  21. ↑ Tryptophan, serotonin, and aging, raypeat.com, 2006
  22. ↑ Serotonin: Energy, Degeneration, and Aging, Ray Peat Newsletter, July 2019
  23. ↑ 23.0 23.1 23.2 23.3 Ray Peat, "Thyroid, insomnia, and the insanities," raypeat.com.
  24. ↑ Thyroid, insomnia, and the insanities
  25. ↑ Thyroid, insomnia, and the insanities, raypeat.com
  26. ↑ Anthony M. "Serotonin antagonists," Aust N Z J Med. 1984;14(6):888-895. PMID 6398056.
  27. ↑ Brown L, Rosellini RA, Samuels OB, Riley EP. "Evidence for a serotonergic mechanism of the learned helplessness phenomenon," Pharmacol Biochem Behav. 1982;17(5):877-83. doi:10.1016/0091-3057(82)90465-8. PMID 6891069. Rodent study.
  28. ↑ Amat J, Baratta MV, Paul E, Bland ST, Watkins LR, Maier SF. "Medial prefrontal cortex determines how stressor controllability affects behavior and dorsal raphe nucleus," Nat Neurosci. 2005;8(3):365-371. doi:10.1038/nn1399. PMID 15696163. Rat study.
  29. ↑ Endotoxin, stress, depression, Ray Peat Newsletter, May 2011
  30. ↑ 30.0 30.1 Andrews PW, Bharwani A, Lee KR, Fox M, Thomson JA Jr. "Is serotonin an upper or a downer? The evolution of the serotonergic system and its role in depression and the antidepressant response," Neurosci Biobehav Rev. 2015;51:164-188. doi:10.1016/j.neubiorev.2015.01.018. PMID 25625874.
  31. ↑ Ray Peat, "Ask the Herb Doctor: Brain "Barriers"", KMUD, 49:04
  32. ↑ Koren-Schwartzer N, Chen-Zion M, Ben-Porat H, Beitner R. "Serotonin-induced decrease in brain ATP, stimulation of brain anaerobic glycolysis and elevation of plasma hemoglobin; the protective action of calmodulin antagonists," Gen Pharmacol. 1994;25(6):1257-1262. PMID 7875554.
  33. ↑ Lee JS, Kang JY, Park SY, Hwang SJ, Bae SJ, Son CG. "Central 5-HTergic hyperactivity induces myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS)-like pathophysiology," J Transl Med. 2024;22:34. doi:10.1186/s12967-023-04808-x. PMID 38191373. PMC10773012.
  34. ↑ Healy D, Mangin D. "Post-SSRI sexual dysfunction: barriers to quantifying incidence and prevalence," Epidemiol Psychiatr Sci. 2024;33:e40. doi:10.1017/S2045796024000441. PMID 39289881.
  35. ↑ Bala A, Nguyen HMT, Hellstrom WJG. "Post-SSRI Sexual Dysfunction: A Literature Review," Sex Med Rev. 2018;6(1):29-34. PMID 28778697.
  36. ↑ Klaas S, Siva JB, Bak M, Govers M, Schreiber R. "The pathophysiology of Post SSRI Sexual Dysfunction - Lessons from a case study," Biomed Pharmacother. 2023;161:114166. PMID 36898260.
  37. ↑ Salisbury AL, et al. "Fetal behavior and gestational serotonin reuptake inhibitor exposure: relationships between behavior, drug dosage, plasma drug level, and a measure of drug bioeffect," Neuropsychopharmacology. 2024. doi:10.1038/s41386-024-01923-1. PMID 39127823.
  38. ↑ Zhong X, Harris G, Smirnova L, et al. "Antidepressant Paroxetine Exerts Developmental Neurotoxicity in an iPSC-Derived 3D Human Brain Model," Front Cell Neurosci (2020).
  39. ↑ Matityahu L, Hobel ZB, Berkowitz N, et al. "Synchronous activation of striatal cholinergic interneurons induces local serotonin release," Nat Commun. 2026;17(1):2278. doi:10.1038/s41467-026-70359-6. PMID 41839847.
  40. ↑ Crane JD, Palanivel R, Mottillo EP, et al. "Inhibiting peripheral serotonin synthesis reduces obesity and metabolic dysfunction by promoting brown adipose tissue thermogenesis," Nat Med. 2015;21(2):166-172. PMID 25485911.
  41. ↑ Dugué GP, Mainen ZF. "How serotonin gates olfactory information flow," Nat Neurosci. 2009;12(6):673-675. doi:10.1038/nn0609-673. PMID 19471262.
  42. ↑ Wutzler A, Winter C, Kitzrow W, et al., Juckel G. "Loudness dependence of auditory evoked potentials as indicator of central serotonergic neurotransmission: simultaneous electrophysiological recordings and in vivo microdialysis in the rat primary auditory cortex," Neuropsychopharmacology. 2008;33(13):3176-3181. doi:10.1038/npp.2008.42. PMID 18463629.
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  76. ↑ Ray Peat, "EastWest Healing: Questions and Answers I", EastWest Healing, 54:37
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