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Not medical advice. The Atlas is not a substitute for a clinician who can examine you.

L-Glutamine

L-Glutamine · The Most Abundant Plasma Amino Acid

Evidence grade 2 of 5, Thin. Read how the Atlas grades evidence.

The blanket grade of 3 overstates what holds across the marketed uses, so the honest split lands lower for the consumer story and higher for narrow clinical ones. For the sports and general-wellness claims that sell most glutamine powder, the evidence is preliminary at best. The 2019 systematic review and meta-analysis by Ahmadi and colleagues in Clinical Nutrition (47 studies, 25 in the pooled analysis) concluded glutamine has no effect on athletic aerobic performance, immune markers, or body composition in healthy people, which supports a grade of 2 for that halo. The picture flips for specific clinical settings. Oral pharmaceutical glutamine (Endari) earned FDA approval in July 2017 on the strength of Niihara and colleagues' 230-patient Phase 3 randomized trial in the New England Journal of Medicine showing roughly 25 percent fewer sickle cell pain crises and 33 percent fewer hospitalizations, which is closer to grade 4 for that indication. Critical-illness use once looked strong on early meta-analysis but was reversed by the large REDOXS (1,223 patients) and MetaPlus trials, which signaled higher mortality with high-dose glutamine, so major guidelines now advise against it. The recommendation of 2 reflects the everyday consumer purchase; the clinical exceptions are graded separately in the text.

FDA
Legal supplement (DSHEA); Rx (Endari for sickle cell)
WADA
Not prohibited

Reference only. Not medical advice.

What can go wrong

Well tolerated in healthy adults, but avoid high-dose IV use in critical illness and use caution in cirrhosis, active cancer treatment, and pregnancy without clinician oversight.

L-Glutamine is the most abundant free amino acid in human plasma and skeletal muscle, and it is classed as conditionally essential, meaning the body usually makes enough on its own but may not during severe stress like burns, sepsis, or major trauma. That biology fuels a large supplement market aimed at muscle recovery and gut repair, yet the strongest human evidence sits in narrow clinical settings rather than the gym. A 2019 meta-analysis found no benefit for athletic performance, immune function, or body composition in healthy people. The clearest win is a prescription version, Endari, which the FDA approved in 2017 to reduce complications of sickle cell disease. The honest read is a real medical amino acid whose consumer marketing runs well ahead of the supplement data.

A critical-care amino acid with consumer marketing that exceeds the supplement evidence.

What people take it for

These are the reasons people give for taking it. They are not effects it has been shown to have.

  • Reducing acute complications of sickle cell disease (prescription Endari, FDA-approved)
  • Critical illness and ICU nutrition (historically studied, now largely discouraged)
  • Inflammatory bowel disease as an adjunct (mixed, mostly small trials)
  • Intestinal barrier and permeability support (preliminary)
  • Athletic recovery and muscle building (marketed, not supported in healthy people)
  • Chemotherapy or radiation mucositis symptom relief (adjunct, variable)

How it is supposed to work

L-glutamine is the most abundant free amino acid in human plasma and skeletal muscle, about 50-60% of the free amino acid pool. The body synthesizes it from glutamate, branched-chain amino acids, and ammonia through glutamine synthetase, with substantial production in skeletal muscle, lung, and adipose tissue. Glutamine serves multiple critical functions: nitrogen transport between tissues, primary fuel for rapidly dividing cells (enterocytes, lymphocytes, immune cells generally), substrate for glutathione synthesis, ammonia detoxification in the liver and brain, and acid-base balance through renal ammoniagenesis. Under normal physiology, endogenous synthesis is sufficient, glutamine is non-essential. Under severe metabolic stress (sepsis, major burns, post-surgical trauma, intense catabolic states), glutamine demand exceeds synthesis and plasma levels decline, making glutamine "conditionally essential" in critical illness. The gut barrier mechanism is the most-cited consumer claim and the most nuanced clinical evidence. Intestinal enterocytes use glutamine as primary fuel; glutamine supplementation supports enterocyte proliferation and tight junction integrity in tissue culture and animal models. In humans, the strongest evidence is in burn patients and critical illness where intestinal barrier function is genuinely compromised. The translation to consumer "leaky gut" or "gut healing" use cases is far less established, most healthy adults consuming adequate dietary protein have sufficient endogenous glutamine for normal enterocyte function. The athletic recovery and immune function consumer marketing significantly exceeds the supplement-level evidence; high-dose glutamine's clinical successes are in critical illness, not gym recovery.

How it is taken

Glutamine dosing varies dramatically by indication. Clinical ICU protocols use 20-40g/day intravenously; sickle cell disease uses 5g three times daily orally; IBS with permeability uses 5g three times daily; consumer recovery use typically 5-10g/day. The pharmacokinetics support divided dosing (3-4 times daily) over single large doses, plasma peaks within 30-45 minutes and clears within 2-3 hours. Take with or without food. Powder form mixes easily in water or juice. The dose hierarchy follows evidence strength: pharmaceutical indications (sickle cell) at clinical doses are well-supported; consumer wellness use is poorly supported regardless of dose. The REDOXS finding constrains very high IV doses in critically ill mechanically ventilated patients; oral supplement doses in stable outpatients do not carry this concern.

Sickle cell (Endari)
5g three times daily, prescription
IBS with permeability
5g three times daily for 8 weeks
IBD adjunct
5-15g/day with specialist coordination
Consumer recovery
5-10g/day post-exercise; weak evidence
ICU / burns
20-40g/day parenteral, hospital protocol
Divided dosing
3-4 times daily preferred over single dose
Food state
With or without food
Active cancer
Avoid without oncology guidance

Which form to buy

Not all preparations of the same ingredient are the same thing, and the trials were run on particular ones.

  • L-Glutamine Powder (Pharmaceutical Grade)

    Rating: gold

    Pure crystalline L-glutamine, the form used in essentially all clinical trials. Easily mixed with water or juice; relatively tasteless. Cost-effective compared to capsules at therapeutic doses (5-30g requires many capsules but a small scoop). Brands: Thorne, NOW, Bulk Supplements with USP verification.

  • L-Glutamine Capsules

    Rating: good

    Capsule format typically delivers 500-1000mg per capsule. Practical for low-dose use (1-5g/day) but inconvenient and expensive at therapeutic ICU-equivalent doses. Acceptable consumer format for lower-dose protocols.

  • Endari® (Pharmaceutical L-Glutamine)

    Rating: gold

    Emmaus Life Sciences FDA-approved pharmaceutical L-glutamine for sickle cell disease. 5g per dose, three times daily. Insurance coverage and prescription required. Same compound as supplement; pharmaceutical specification and indication.

  • Alanyl-L-Glutamine (Dipeptiven)

    Rating: good

    Stabilized dipeptide form used in IV nutrition (parenteral). More stable in solution than free L-glutamine. Hospital ICU and parenteral nutrition use; not typical consumer supplement.

  • BCAA + Glutamine Combinations

    Rating: good

    Common athletic recovery formulations combining glutamine with branched-chain amino acids. Mechanistically reasonable (BCAAs are glutamine precursors); evidence for combination benefit beyond individual components is modest.

  • "Gut Healing" Protein Powders

    Rating: caution

    Multi-ingredient protein blends combining glutamine with collagen, bone broth, herbs, and other ingredients. Marketing-driven consumer "leaky gut" products. Glutamine content often subclinical relative to therapeutic protocols. Verify actual glutamine dose.

  • N-Acetyl-L-Glutamine

    Rating: caution

    Marketed for "better stability" or "absorption." Limited head-to-head clinical evidence versus standard L-glutamine. Premium pricing for marginal documented benefit.

Who it works for, and who it does not

  • Critical illness / ICU (parenteral)

    Strength of evidence for this group: strong

    The strongest evidence, pre-REDOXS. Parenteral glutamine 20-40g/day reduced infectious complications and ICU length of stay in mechanically ventilated and post-surgical patients. Heyland REDOXS 2013 complicated routine high-dose use in mechanically ventilated patients with multi-organ failure.

  • Sickle cell disease

    Strength of evidence for this group: strong

    Endari (5g three times daily) reduced pain crises and hospitalizations in the FDA pivotal trial. First FDA-approved L-glutamine indication. Coordinate with hematology rather than self-supplementing.

  • Major burns (>20% TBSA)

    Strength of evidence for this group: modest

    Enteral glutamine supplementation in major burns reduces wound infections and may shorten length of stay. Established clinical nutrition practice; specialist administration.

  • Inflammatory bowel disease

    Strength of evidence for this group: cautious

    Mixed evidence in Crohn's disease and ulcerative colitis. Mechanistically plausible (enterocyte fuel, barrier function); clinical trials inconsistent. Reasonable adjunct under gastroenterology guidance.

  • Postinfectious IBS with permeability

    Strength of evidence for this group: modest

    Benjamin 2014 trial supports modest symptom improvement at 5g three times daily. Most positive evidence in confirmed intestinal permeability rather than general IBS. Reasonable trial in this specific subgroup.

  • Chemotherapy mucositis

    Strength of evidence for this group: modest

    Mouthwash and oral glutamine has modest evidence for reducing chemotherapy-induced mucositis. Symptomatic adjunct under oncology guidance.

  • Endurance athletes for immune function

    Strength of evidence for this group: weak

    The popular consumer use case, but Gleeson 2008 and subsequent reviews have not supported the immune function or performance claims. Most athletes maintain adequate endogenous glutamine through diet and training adaptation.

  • General "leaky gut" or consumer wellness

    Strength of evidence for this group: weak

    Most healthy adults with adequate dietary protein have sufficient endogenous glutamine. The consumer "leaky gut" marketing significantly exceeds the supplement-level evidence. Specific clinical situations (documented permeability, IBD, postinfectious) are different from general wellness use.

  • Active cancer (some tumor types)

    Strength of evidence for this group: cautious

    Many tumors use glutamine as primary fuel (the Warburg-like glutaminolysis phenomenon). High-dose supplementation may theoretically support tumor growth in some cancers. Coordinate with oncology during active treatment.

Taken with other things

Combinations people actually use. Evidence for one ingredient is not evidence for a pair.

  • BCAAs (Leucine, Isoleucine, Valine)

    Interaction: synergy

    Mechanistically related, BCAAs are precursors for endogenous glutamine synthesis. Combined supplementation is common in athletic recovery formulations. Modest additive evidence beyond individual components.

  • Probiotics

    Interaction: synergy

    Common gut-health protocol pairing. Glutamine supports enterocyte function; probiotics modulate microbiome. Mechanistically complementary; clinical combination evidence limited.

  • Zinc-Carnosine

    Interaction: synergy

    Both have evidence for gut barrier function. Common combination in functional medicine gut protocols.

  • Collagen Peptides

    Interaction: synergy

    Combined in gut-health protein blends. Different mechanisms; mechanistically complementary for gut barrier support.

  • Active cancer treatment

    Interaction: avoid

    Many tumors use glutamine as fuel via glutaminolysis. High-dose supplementation may theoretically support tumor growth. Oncology coordination essential during active treatment.

  • Liver cirrhosis / hepatic encephalopathy

    Interaction: caution

    Glutamine is converted to ammonia in the liver; impaired hepatic function can produce ammonia accumulation and encephalopathy. Avoid in advanced liver disease.

  • Lactulose / hepatic encephalopathy treatment

    Interaction: caution

    Lactulose reduces ammonia production; glutamine supplementation may counter this mechanism. Avoid in patients on lactulose for HE.

  • MSG sensitivity

    Interaction: neutral

    Glutamate is the metabolic neighbor; some MSG-sensitive individuals report sensitivity to high-dose glutamine. Individual response variable.

What to look for on the label

Look for: USP verification or third-party testing (NSF, Informed Sport); pharmaceutical-grade specification for clinical use; explicit L-glutamine (not D-glutamine, which is inactive); manufacturer disclosure and reputation; fermentation source disclosure (corn vs wheat) for sensitive users. Avoid: products that don't specify L-isomer; proprietary "gut healing" blends without explicit glutamine dose disclosure; very cheap products without third-party verification; products claiming dramatic "leaky gut" cures without specific clinical indication.

Safety in detail

  • Generally very safe at supplement doses (5-30g/day) in healthy adults. No serious adverse events in clinical trials at typical doses.
  • Mild GI upset (nausea, bloating) is the most common side effect, particularly at high single doses; resolved by dividing dose.
  • Cirrhosis and hepatic encephalopathy: real contraindication. Glutamine converts to ammonia in the liver; impaired hepatic function can produce ammonia accumulation.
  • Active cancer: theoretical concern about supporting tumor glutaminolysis. Many tumors (lung, breast, colon, glioma) depend on glutamine. Oncology coordination essential.
  • The REDOXS 2013 finding: high-dose parenteral glutamine in critically ill ventilated patients with multi-organ failure increased mortality. Constrains ICU use but does not apply to oral supplement doses in stable outpatients.
  • Pregnancy and breastfeeding: limited systematic safety data at supplement doses. Endogenous glutamine production continues; supplementation not routinely recommended without OB-GYN guidance.
  • Pediatric: limited safety data at supplement doses. Specific pediatric clinical indications (sickle cell) under hematology guidance.
  • Drug interactions: minimal at typical doses. No major documented interactions with cardiovascular or metabolic medications.
  • Source considerations: most modern glutamine is fermentation-derived (corn or wheat substrate). Specific sourcing matters for users with corn/wheat sensitivities.

What people get wrong

  • Often saidGlutamine heals leaky gut.

    ActuallyThe mechanism (enterocyte fuel) is real; the clinical translation to general consumer populations with documented intestinal permeability is much narrower than the consumer marketing suggests. Postinfectious IBS with measured permeability has modest trial evidence; general "leaky gut wellness" does not.

  • Often saidAthletes need glutamine for recovery and immunity.

    ActuallyGleeson 2008 and subsequent reviews have not supported athletic recovery or immune function claims in healthy athletes with adequate dietary protein. The marketing exceeds the supplement-level evidence.

  • Often saidHigher dose glutamine is always better.

    ActuallyThe REDOXS finding shows the opposite in critical illness, high-dose IV glutamine increased mortality. For consumer use, doses above clinical study protocols (typically 5g three times daily) have not been shown to produce proportionally better outcomes.

  • Often saidGlutamine is fine for everyone.

    ActuallyCirrhosis and hepatic encephalopathy are real contraindications. Active cancer raises theoretical concerns about supporting tumor glutaminolysis. Most healthy adults tolerate well, but the universal-safety framing oversimplifies.

  • Often saidGlutamine is essential.

    ActuallyConditionally essential, meaning the body normally synthesizes enough but exogenous supplementation becomes necessary in severe metabolic stress. Most healthy adults with adequate dietary protein have sufficient endogenous glutamine for normal function.

  • Often saidL-glutamine and N-acetyl-glutamine are interchangeable.

    ActuallyDifferent forms with different pharmacokinetics. Clinical evidence is on L-glutamine; N-acetyl-glutamine is less well-studied for the same endpoints.

  • Often saidGlutamine protein powders are the best source.

    ActuallyWhole protein from diet typically provides more total glutamine than supplement powders. Whey, casein, and meat protein contain substantial glutamine. The supplement form is useful for therapeutic doses above what diet provides.

Who profits, and who pushes back

  • Heyland REDOXS investigators

    Pushes back2013 landmark ICU trial

    Our trial of high-dose IV glutamine plus antioxidants in mechanically ventilated patients with multi-organ failure showed increased mortality versus placebo. The finding constrains routine high-dose ICU glutamine use and reshaped the clinical nutrition literature. Hospital protocols have been substantially updated.

  • Gleeson athletic glutamine review

    Pushes backAthletic literature review

    Despite extensive marketing of glutamine for athletic recovery and immune function, our systematic review of trials in healthy athletes found minimal evidence of meaningful performance or immune benefit. The marketing exceeds the supplement-level evidence.

  • Mainstream gastroenterology

    Pushes backClinical practice guidelines

    L-glutamine is not incorporated into mainstream IBD or IBS treatment guidelines as routine therapy. Specific cohorts (postinfectious IBS with documented permeability) may benefit; the broad consumer "leaky gut" marketing does not align with guideline-level evidence.

  • Wiley Souba

    Promotes itHarvard surgical research · ICU glutamine

    Career-defining work on glutamine metabolism in critical illness. Foundational ICU evidence. Independent academic voice; some industry collaboration disclosed.

  • Paul Wischmeyer

    Promotes itDuke critical care

    Lead author of multiple ICU glutamine meta-analyses. Academic voice on hospital glutamine evidence. Industry consulting relationships disclosed.

  • Emmaus Life Sciences

    Sells this. Has a commercial interest in a product sold as this compound, as of July 2026.

    Promotes itEndari manufacturer

    Pharmaceutical L-glutamine manufacturer; sponsored sickle cell pivotal trial leading to 2017 FDA approval. Disclosed industry source for the SCD evidence base.

  • Functional medicine community

    Sells this. Has a commercial interest in a product sold as this compound, as of July 2026.

    Promotes itIFM and adjacent practitioners

    Long-standing advocates for glutamine in "leaky gut" protocols. Commercial interests in supplement sales and consulting practices. Evidence base for consumer use case substantially exceeds what trials support.

  • Dr. Will Cole

    Sells this. Has a commercial interest in a product sold as this compound, as of July 2026.

    Promotes itFunctional medicine clinic

    Aggressive consumer marketer of gut-health protocols including glutamine. Multiple supplement line commercial interests disclosed. Framing has been consistently pro-supplement.

  • Bodybuilding / supplement industry

    Sells this. Has a commercial interest in a product sold as this compound, as of July 2026.

    Promotes itMass-market sports nutrition

    Substantial commercial interest in athletic glutamine marketing. The marketing of athletic and immune benefits has long preceded supportive trial evidence.

How we got here

Hermann Schulze isolated glutamine from beet juice in 1883, among the earliest characterized amino acids. Hans Krebs (later Nobel laureate for the citric acid cycle) elucidated glutamine's role in nitrogen transport and ammonia detoxification in the 1930s. For most of the early 20th century, glutamine was a metabolic biochemistry curiosity rather than a clinical or supplement compound. The critical care era began in the 1980s-90s with Wiley Souba's laboratory at Harvard establishing glutamine as conditionally essential in critical illness. Souba's work on intestinal glutamine metabolism showed that the gut consumes substantial glutamine during sepsis and trauma, with plasma levels declining as supply exceeds endogenous synthesis. Hospital nutrition support protocols incorporated parenteral glutamine through the 1990s-2000s based on multiple meta-analyses (Wischmeyer 2002, 2007, 2014) showing reduced infectious complications. The 2013 REDOXS trial (Heyland et al, Canadian Critical Care Trials Group) complicated this, high-dose IV glutamine plus antioxidants increased mortality in mechanically ventilated patients with multi-organ failure. ICU glutamine use has been recalibrated since. The sports nutrition era ran parallel through the 1990s-2000s, building on early work suggesting glutamine might support immune function in overtrained athletes. The supplement market grew to hundreds of millions in annual sales, but the trial evidence in healthy athletes has been substantially less convincing than the marketing (Gleeson 2008 review and subsequent literature). The sickle cell breakthrough came in 2017 when the FDA approved Endari based on pivotal Phase 3 evidence in pediatric and adult sickle cell patients, the first FDA approval for L-glutamine and a meaningful indication for a vulnerable population. Consumer "leaky gut" marketing accelerated through the 2010s with functional medicine practitioner endorsement; clinical trial evidence in general consumer populations has not kept pace with the marketing claims.

  1. 1883Schulze isolates glutamine from beet juice
  2. 1935Krebs characterizes glutamine synthesis and ammonia metabolism
  3. 1980s-90sSouba laboratory establishes critical illness conditional essentiality
  4. 1990sHospital parenteral glutamine protocols emerge
  5. 2002Wischmeyer ICU meta-analysis supports parenteral glutamine
  6. 2008Gleeson review constrains athletic claims
  7. 2013REDOXS trial complicates high-dose ICU use
  8. 2014Benjamin trial supports IBS with permeability indication
  9. 2017FDA approves Endari for sickle cell disease
  10. 2020sConsumer "leaky gut" marketing continues to exceed evidence

What we do not know

  • Why the REDOXS high-dose IV glutamine finding increased mortality in critically ill patients, whether mechanism, dose, or specific cohort.
  • Whether the consumer "leaky gut" use case has any meaningful clinical effect in healthy adults with normal protein intake.
  • Whether the FDA-approved Endari indication (sickle cell disease) generalizes to other hemoglobinopathies.
  • Whether glutamine's role in cancer cell metabolism (glutaminolysis) translates to clinically meaningful tumor support in cancer patients using supplements.
  • Whether divided dosing (3-4x daily) versus single daily dose produces different clinical outcomes for non-hospital indications.
  • Whether postinfectious IBS with documented permeability represents a distinct cohort with consistent glutamine response versus general IBS.

The market for this

What follows describes how this is bought and sold. It is not a buying guide and it is not an endorsement of any seller.

Modern glutamine production is dominated by bacterial fermentation (typically Corynebacterium glutamicum on corn or wheat substrates). Pharmaceutical-grade and supplement-grade material come from the same fermentation processes with different purification specs. USP-grade verification is the practical quality marker for consumer supplements. Some niche manufacturers offer non-corn (wheat-derived) glutamine for corn-sensitive users; verify on label. The pharmaceutical Endari is manufactured by Emmaus Life Sciences with FDA-approved specs distinct from supplement-grade material.

At a glance

Plasma abundance
Most abundant free amino acid (~500-700 μM)
Body production
Skeletal muscle, lung, adipose
Status
Conditionally essential (essential in critical illness)
Standard supplement dose
5-10g/day consumer; 5g three times daily clinical
Sickle cell (Endari)
5g three times daily
ICU protocol
20-40g/day parenteral (pre-REDOXS)

What this entry does not yet cover

What follows is unfinished work on our side, not a finding about L-Glutamine. A short entry is not a safe entry.

  • Cost and market. We have not documented what it sells for or who sells it.
  • Supply chain. We have not mapped where it is made.
  • Who uses it. We have not documented the user groups.
  • What could change. No forward-looking summary yet.
  • How it compares. We have not set it against the alternatives.
  • Children and teenagers. We have not checked what is known about younger people.
  • Where we land. We have not taken a position on this yet.

Sources

The studies that matter

  • Hermann Schulze isolation1883

    German chemist Schulze isolated glutamine from beet juice and characterized its structure. Foundational biochemistry that named the compound.

  • Hans Krebs glutamine synthesis1935

    Krebs characterized glutamine synthesis and ammonia detoxification, foundational metabolic biochemistry. Krebs later won the Nobel Prize for citric acid cycle work that connects to glutamine metabolism.

  • Souba enteral glutamine ICU trials1990s

    Wiley Souba's laboratory at Harvard established glutamine as conditionally essential in critical illness. Foundational ICU evidence that defined the modern clinical use case.

  • Wischmeyer ICU glutamine meta-analyses2002-2014

    Multiple pooled analyses of parenteral glutamine in critical illness: meaningful reductions in infectious complications and ICU length of stay at IV doses 20-40g/day. The robust hospital-medicine evidence.

  • Heyland REDOXS trial2013

    Large multicenter Canadian trial of high-dose glutamine + antioxidants in critically ill patients: surprisingly increased mortality versus placebo. Reshaped the ICU glutamine literature, high-dose IV glutamine no longer routine in mechanically ventilated patients.

  • Gleeson athletic glutamine review2008

    Pooled analysis of glutamine in athletic populations: minimal evidence for immune function improvement or performance enhancement in healthy athletes. The athletic literature has not supported the marketing claims.

  • Niihara FDA Endari approval2017

    Phase 3 trial of L-glutamine (5g/dose, 3x daily) in sickle cell disease: significant reduction in pain crises and hospitalizations. FDA approved Endari (pharmaceutical L-glutamine) for sickle cell disease, the first FDA approval for this indication.

  • Benjamin IBS glutamine trial2014

    Glutamine supplementation in postinfectious IBS with intestinal permeability: modest symptom improvement at 5g three times daily. Among the better consumer-application clinical evidence.

  • Severo crohn glutamine review2019

    Mixed evidence in inflammatory bowel disease, some trials positive, others null. Mechanistically plausible but clinical inconsistency.