L-Glutamine: Uses, Benefits, Dosage & Safety

Last updated: June 2026 · Reviewed by the FactoWiki Editorial Team for clarity and source accuracy

What is L-Glutamine?

Glutamine is the most abundant free amino acid in the body and is described as 'conditionally essential' — usually made in plenty, but demand can outstrip supply during serious illness, injury or major surgery. It is a primary fuel for the cells that line the gut and for immune cells, which is why it has long been studied in hospital nutrition and, more recently, in endurance athletes whose guts take a beating during prolonged effort.

What L-Glutamine is commonly used for

In supplements, L-Glutamine is taken mainly for gut & digestive health, for immune and recovery support, and around intense exercise. It is sold as nutritional support; the strong clinical evidence comes from medically supervised settings, and the everyday gut and recovery uses are more modest than the marketing suggests.

How L-Glutamine works

Glutamine is fuel for rapidly dividing cells, especially the enterocytes that line the gut and the cells of the immune system. It also helps support the tight junctions that keep the gut barrier sealed. Under heavy physical stress — critical illness or prolonged intense exercise — that barrier can become more permeable, sometimes called a 'leaky gut,' and supplying extra glutamine appears to help maintain it. Its role in muscle is real, but a healthy body usually makes enough, which is why supplements rarely add much for ordinary lifters.

What the evidence says

Here's an honest snapshot of what published research suggests about L-Glutamine — including where the evidence is limited.

• A controlled trial found that seven days of oral glutamine reduced exercise-induced intestinal permeability — a measure of gut-barrier 'leakiness' — compared with placebo. (PubMed)
• A randomised study found glutamine reduced markers of intestinal permeability during running in the heat in a dose-dependent way. (PubMed)
• General background on glutamine and its uses is summarised by reputable health references. (MedlinePlus)

Typical dosage used in studies

Research doses vary widely depending on the purpose. Exercise and gut studies have used roughly 0.9 g per kg of body weight or fixed doses in the 5–20 g range; clinical use in hospitals is different and supervised. Effects on the gut barrier are seen over days of use. This is general information from research, not a recommendation.

Side effects and safety

Glutamine is generally well tolerated in healthy people, even at relatively high doses, with mild digestive effects being the most common complaint. Because it adds to the body's amino-acid and nitrogen load, people with liver or kidney disease should avoid high doses unless supervised.

Medication interactions and who should avoid L-Glutamine

Sources & further reading

The evidence summary above is drawn from these sources. For general, authoritative background you can also consult:

• PubMed-indexed study (PMID 24285149)
• PubMed-indexed study (PMID 29058112)
• MedlinePlus
• NIH Office of Dietary Supplements
• NIH National Center for Complementary and Integrative Health

Frequently asked questions

Does glutamine fix a 'leaky gut'?

Small studies show it can reduce exercise-induced increases in gut permeability, which is a specific, measurable effect. The broader internet idea of 'curing leaky gut' for general symptoms is not well supported by evidence.

Does glutamine build muscle?

The body usually makes enough glutamine on its own, and evidence that supplements add meaningful muscle or strength in healthy people is weak. Its better-supported roles are in the gut and immune system under stress.

Who benefits most from glutamine?

The strongest evidence is in clinical settings such as critical illness, burns and major surgery, under medical supervision. Among healthy people, endurance athletes with gut symptoms are the group most likely to notice anything.

How much glutamine is used in studies?

It varies a lot — gut and exercise research has used roughly 5–20 g, or doses scaled to body weight. There is no single agreed dose, so this is general information rather than advice.

Is glutamine safe?

For most healthy people it is well tolerated, even at higher doses. People with liver or kidney disease should avoid high doses unless supervised, and anyone on medication should check first.