Quick answer

L-glutamine is the most abundant amino acid in your muscle and blood, and adults eat about 3 to 6 g a day in protein foods. Trials in healthy adults have not shown gains in strength, lean mass or immune measures, and the few positive results used about 15 g or more at a time.^1,2,3,4

Key facts

The body makes its own glutamine, mainly from the BCAAs.¹
A meta-analysis of 25 trials in athletes found no effect on immune measures, aerobic performance or body composition.²
Across 10 trials, gut permeability changed only at more than 30 g a day.⁵
No side effects were reported at up to 45 g a day for several weeks in the exercise studies NIH reviewed.⁶

What L-glutamine is

Glutamine is the most abundant amino acid in muscle, in blood and in the body's pool of free amino acids.¹

Glutamine is a key molecule in metabolism and energy production, and it supplies nitrogen for many of the body's chemical reactions.¹

Muscle makes most of the body's glutamine, largely from the BCAAs, and fast-dividing cells such as those lining the gut and immune cells use it as fuel. In serious illness or injury, demand can outrun supply, which is why glutamine is used in medical nutrition. In healthy adults the body normally makes enough.^1,7

Long, exhausting exercise is linked to a dip in blood glutamine. A review found the dip is not deep enough to hold back immune cells, and that keeping blood glutamine steady during and after exercise did not stop the changes in immune function seen after hard sessions.⁸

What the research shows

Both claims below are graded early, and both say plainly that a benefit is unproven. They describe what glutamine is for in the body, not what a supplement has been shown to do.

Supplies glutamine, a fuel for cells of the gut lining; a benefit from 3 g a day is unproven*^3,5,7,9

Early evidence

The fuel role is established physiology. But a 2024 meta-analysis of 10 trials (352 adults, mostly people under medical care) found no overall effect on gut permeability, with an effect only at more than 30 g a day. In 10 men running in the heat, single doses of about 15 to 54 g lowered a marker of gut permeability, while about 20 g did not help in another trial of 10 men. None of these tested a dose near 3 g.

Amount studied: Single doses of about 15 to 54 g before exercise, and more than 30 g a day in trials of people under medical care

Adds to the body's own glutamine during very heavy training, when blood levels can dip; a benefit is unproven*^1,2,8

Early evidence

Prolonged, exhausting exercise is linked to a fall in blood glutamine. But a meta-analysis of 25 trials in athletes concluded that glutamine generally has no effect on immune measures, aerobic performance or body composition, and the NIH says research does not support taking glutamine alone to improve performance. One trial in 16 adults found less soreness and faster strength recovery at about 0.3 g per kg of body weight a day, roughly 21 g for a 70 kg person.

Amount studied: About 0.3 g per kg of body weight a day in the soreness trial, roughly 21 g for a 70 kg adult; up to about 45 g a day in others

In a 6-week trial, 31 young adults took almost 45 g a day while resistance training and gained no more strength or lean mass than the placebo group.^1,10

Soreness and strength recovery. The one positive trial crossed 16 young adults, 8 women and 8 men, between glutamine and placebo. At 0.3 g per kg a day over the 3 days around a hard leg session, soreness ratings were lower at 24, 48 and 72 hours and leg strength came back faster, more clearly in the men. It has not been repeated.⁴

A meta-analysis of 25 trials in athletes found that glutamine generally had no effect on immune measures, aerobic performance or body composition.²

The gut in hot conditions. In 10 men running for an hour in the heat, single doses of about 15 to 54 g taken 2 hours before lowered a marker of gut permeability, most at the largest dose. In another 10 men, about 20 g taken an hour before exhausting exercise in the heat slightly worsened the same kind of marker.^3,9

The bottom line from NIH is that research does not back taking glutamine alone for exercise and athletic performance, and the International Society of Sports Nutrition puts it in its little to no evidence group for muscle building and performance.^1,11

Glutamine in food

Meat, poultry, fish, eggs, dairy products and legumes supply glutamine as part of their protein.⁶

Adults take in about 3 to 6 g of glutamine a day from protein foods, and the body makes more.^1,6

Supplements sell L-glutamine as a single amino acid. Protein foods, protein powders and protein hydrolysates also supply glutamine, so athletes who eat a lot of protein can take in large amounts without a separate supplement.⁸

Amounts used in studies

The trials used far more than food or a typical scoop provides: 0.3 g per kg of body weight a day in the soreness trial, about 21 g for a 70 kg adult; almost 45 g a day in the 6-week training trial; and single doses of about 15 to 54 g before exercise in the heat. The dosage guide sets these out by body weight.^3,4,10

What's in ours

What’s in ours

BCAA 2:1:1: L-Glutamine, 1,000 mg per serving, from the label

Both amounts, 3.15 g and 1 g, are around or below what food already supplies in a day, and well below the amounts in any trial above.¹

Side effects, and who should ask first

No side effects were reported in the exercise trials summarized by NIH, which used up to 45 g a day for several weeks.^1,6

No tolerable upper intake level is set for glutamine. NIH reports no evidence of toxicity at 0.21 to 0.42 g per kg of body weight a day (15 to 30 g for a 154 lb person) and no safety concerns at about 45 g a day for 6 weeks. A review notes that single doses of about 20 to 30 g appear to be without ill effect in healthy adults.^1,8

Glutamine is broken down to ammonia, and a safety review says high intakes are inappropriate for people with liver or kidney impairment.⁷

Ask your doctor first if you have liver disease or a urea cycle disorder, since glutamine is broken down to ammonia⁷
Ask first if you have kidney disease or reduced kidney function, or if you have cancer or are in cancer treatment⁷
Ask first if you are pregnant or breastfeeding: the prescription L-glutamine label says there are no data in pregnancy¹²
If you take prescription L-glutamine, do not add a supplement on top without your prescriber's approval¹³

No official source we checked documents an interaction between glutamine and a medicine, and the prescription L-glutamine label says no drug interaction studies have been done. That is an absence of evidence, not proof of safety, so tell your pharmacist about it like any other supplement.¹²

Questions people ask

Does L-glutamine help the gut?

Glutamine is a fuel for gut cells, but supplement trials are mixed. Pooling 10 trials found no overall change in gut permeability, with a change only above 30 g a day, and the trials in runners in the heat disagreed with each other.^3,5,9

Does L-glutamine build muscle?

Not in the trial that tested it. Young adults who took almost 45 g a day through 6 weeks of resistance training gained the same strength and lean mass as those on placebo.¹⁰

Is L-glutamine good for skin or hair?

We found no trials of glutamine supplements for skin or hair in healthy adults when we searched PubMed, so there is nothing to grade.

I already use protein powder. Do I need glutamine too?

Probably not. Protein foods and protein powders contain glutamine as part of their protein, and your body makes more from the BCAAs.^1,8

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Sources

*These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.

This page is information, not medical advice. Talk to your doctor or pharmacist about your own situation.