L-glutamine
Summary
L-glutamine is a conditionally essential amino acid. A pooled analysis of 25 trials in athletes found no effect on aerobic performance, body composition or immune markers. A prescription L-glutamine powder lowered pain crises in sickle cell disease, and in critically ill patients with organ failure, high-dose glutamine was linked to higher mortality.
Key facts
- The most abundant free amino acid; the body makes it, but needs can rise during severe illness[3]
- No effect on aerobic performance, body composition or immune function across 25 trials (no-effect)[1]
- Oral L-glutamine reduced pain crises over 48 weeks in sickle cell anaemia (phase 3 trial)[2]
- In critically ill adults with multiorgan failure, early high-dose glutamine was associated with higher mortality[3]
- 2 graded human outcomes on this page
- October 11, 2026
How it works
ProposedGlutamine fuels rapidly dividing cells such as gut lining and immune cells and carries nitrogen between tissues. In sickle cell disease it is proposed to raise red-cell NAD and reduce oxidative stress.[2]
What the human research says
Human trials only, one row per outcome. The form column shows what each trial actually tested. Grades follow our evidence-grading policy.
At a glance: strongest evidence per outcome
| Outcome | Grade | Effect | Strongest evidence | Rows |
|---|---|---|---|---|
| Prescription use | Grade B | Improved | RCT · n = 230 · 2018 | 1 row |
| Safety | Grade C | Worsened | RCT · n = 1,223 · 2013 | 1 row |
Every graded row
| Outcome | Effect | Grade | Best evidence | PMID |
|---|---|---|---|---|
| Pain crises in sickle cell anaemia | Improved | Grade B | RCT · n = 230 · 2018 Children and adults (5–58 years) with sickle cell anaemia Form: Pharmaceutical-grade L-glutamine powder · Dose: 0.3 g/kg twice daily (prescription dosing) · Duration: 48 weeks Median pain crises were lower than with placebo, with or without hydroxyurea; nausea, chest pain, fatigue and musculoskeletal pain were more common. | 30021096 (opens PubMed)Source [2] |
| 28-day mortality in critical illness | Worsened | Grade C | RCT · n = 1,223 · 2013 Mechanically ventilated adults with multiorgan failure Form: Intravenous plus enteral glutamine · Dose: High-dose glutamine started within 24 hours of ICU admission (2×2 factorial with antioxidants) · Duration: ICU stay; mortality at 28 days and 6 months 28-day mortality trended higher with glutamine (32.4% vs 27.2%), and in-hospital and 6-month mortality were significantly higher. | 23594003 (opens PubMed)Source [3] |
Forms
| Form | Elemental % | Absorption (human data) | GI tolerance | Studied for |
|---|---|---|---|---|
| Free L-glutamine powder or capsules | Varies | No head-to-head human absorption data in the sources cited here. | Nausea and musculoskeletal pain were more common than placebo in the sickle cell trial.[2] | Exercise and sickle cell trials |
| Alanyl-glutamine (dipeptide) | Varies | Raised post-exercise blood glucose versus control in pooled athlete trials.[1] | No separate tolerance data in the sources cited here. | Some exercise trials |
Studied doses
Doses studied in human trials ranged from a few grams per day in athlete studies to 0.3 g/kg twice daily (prescription dosing) for 48 weeks in sickle cell anaemia.[1][2]
Interactions
Published interactions only: each row cites a source. No row means none was found in our sources, not that a combination is safe.
None found in our sources.
Who should be careful
- Critical illness
- High-dose glutamine increased mortality in ventilated ICU patients with multiorgan failure.[3]
- Sickle cell disease
- The prescription product is dosed by a clinician; supplement powders are not the same regulated product.[2]
Talk to your pharmacist or clinician before starting a supplement, especially if you take prescription medicines.
Where to buy L-glutamine
Products from brands we partner with that contain L-glutamine. Listing a product is not a claim that it works; check the amount per serving against the doses studied above, and the label for other ingredients.
- SupersmartPaid linkL-Glutamine1 serving: 3 g L-glutamine powder; 50 servingsShop at Supersmart (opens in new tab)Price and label checked 2026-10-11 on the brand’s site.
Partner links may earn us a commission. Learn more
Get 15% off with SMART026 (opens in new tab)15% off with code SMART026
Partner links may earn us a commission. Learn more
- Supersmart’s own terms and exclusions apply at checkout.
- 20% applies when 3 or more products ship on auto-delivery to the same address.
- The code discount and Subscribe & Save are separate offers; we don’t claim they combine.
- Offer terms from Supersmart’s site and its affiliate program, checked Oct 8, 2026. Offers can change; the brand's checkout is final.
Frequently asked questions
Does glutamine help muscle growth?
Pooled athlete trials found no effect on body composition or aerobic performance.[1]
Does glutamine help immunity after exercise?
Across 25 trials it did not change immune markers in athletes overall.[1]
Is glutamine an approved medicine?
A pharmaceutical L-glutamine powder is prescribed for sickle cell disease after a phase 3 trial showed fewer pain crises.[2]
Sources
- [1]The effect of glutamine supplementation on athletic performance, body composition, and immune function: A systematic review and a meta-analysis of clinical trials.. Clin Nutr, 2019. meta-analysis
- [2]A Phase 3 Trial of l-Glutamine in Sickle Cell Disease.. N Engl J Med, 2018. RCT
- [3]A randomized trial of glutamine and antioxidants in critically ill patients.. N Engl J Med, 2013. RCT
What changed
- Corrected the effect arrow (↑ improved, ↓ worsened for participants) on: Pain crises in sickle cell anaemia; 28-day mortality in critical illness.
- First draft. Every PMID checked against NCBI E-utilities (title, journal and year taken from the PubMed record) and each evidence row written from its PubMed abstract.