Quick answer

There is no recommended daily amount. Adults get about 3 to 6 g a day from food, and the body makes more. Exercise trials used far larger amounts: 0.3 g per kg of body weight a day, about 21 g for a 70 kg adult, up to almost 45 g a day.^1,2,3

Key facts

NIH reports no toxicity at 0.21 to 0.42 g per kg a day, about 15 to 30 g for a 154 lb person.¹
Gut permeability changed only above 30 g a day in a pooled analysis of 10 trials.⁴
Single doses of about 20 to 30 g appear to be without ill effect in healthy adults.⁵
The prescription L-glutamine powder is dosed at 10 to 30 g a day, by body weight.⁶

The amounts used in studies

The one trial that found less soreness gave 0.3 g per kg of body weight once a day over the 3 days around a bout of hard leg exercise, about 21 g a day for a 70 kg adult.^1,2

A 6-week training trial gave 0.9 g per kg of lean body mass a day, almost 45 g, and found no added gains in strength or lean mass.^1,3

Gut studies gave single doses of 0.25 to 0.9 g per kg of fat-free mass, about 15 to 54 g, 2 hours before running, and 0.3 g per kg of fat-free mass, about 20 g, 1 hour before.^7,8

Glutamine amounts in trials, and what they found^2,3,4,7,8
Trial	Amount	For a 70 kg adult	What was found
Soreness after hard leg exercise, 16 adults	0.3 g per kg a day for 3 days	About 21 g a day	Lower soreness and faster strength return; not repeated
6 weeks of resistance training, 31 adults	0.9 g per kg of lean mass a day	Almost 45 g a day	No extra strength or lean mass
Running in the heat, 10 men	0.25 to 0.9 g per kg of fat-free mass, once	About 15 to 54 g	Lower gut permeability marker
Exhausting exercise in the heat, 10 men	0.3 g per kg of fat-free mass, once	About 20 g	No protection; marker slightly worse
Gut permeability, 10 trials pooled	Various	More than 30 g a day	A change only above this amount

We found no trial in healthy adults of an amount as small as a typical supplement scoop, so nothing is known about what one serving does on its own.

By body weight

At 0.3 g per kg, the amount in the soreness trial, a 60 kg adult would take about 18 g a day and an 80 kg adult about 24 g. Watch which weight a study uses: the training trial counted lean body mass and the heat studies fat-free mass, both lower than total body weight.^2,3,7

NIH's no-toxicity range of 0.21 to 0.42 g per kg a day works out to about 13 to 25 g for a 60 kg adult and 17 to 34 g for an 80 kg adult.¹

What you already get from food

Adults take in about 3 to 6 g of glutamine a day from protein foods, and the body makes more.^1,9

The body makes glutamine itself, mainly from the BCAAs.^1,9

Athletes who eat a lot of protein, or use protein powders, take in more glutamine without a separate supplement, because it is part of the protein.⁵

When and how to take it

Studies of glutamine and the gut gave a single dose 1 to 2 hours before exercise in the heat.^7,8

The soreness trial gave its dose once a day, and the training trial daily through the program. We found no trial that compared times of day, so there is no evidence that morning, evening, or before or after exercise matters at supplement amounts.^2,3

The prescription L-glutamine label says to mix each dose into a cold or room-temperature drink, or into soft food such as applesauce or yogurt, just before taking it. It does not need to dissolve fully.^6,10

What's in ours

What’s in ours

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

Upper amounts, and who should ask first

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.^1,5

The prescription L-glutamine powder is dosed by body weight at 5 to 15 g twice a day, 10 to 30 g a day in all, under a doctor's care.⁶

That prescription powder is a medicine for sickle cell disease, taken under a doctor's care. If you are on it, do not add a supplement on top without your prescriber's approval.^6,10

Ask a doctor before taking glutamine at any amount if you have liver or kidney disease or a urea cycle disorder, are in cancer treatment, are pregnant or breastfeeding, or are under 18.^6,9,11

Questions people ask

Is 5 g of L-glutamine a day enough?

Enough for what has not been shown. Five grams is close to what food already supplies on a protein-rich day, and the trials that found effects used about 15 g or more at a time.^1,2,7

Is 10 g of L-glutamine a day too much?

Not by the studies NIH reviewed, which found no toxicity at 15 to 30 g a day for a 154 lb adult and no safety concerns at about 45 g a day for 6 weeks. People with liver or kidney problems should ask a doctor first.¹

Should I split my glutamine into several doses?

The prescription powder is taken in two doses a day. The soreness trial used one daily dose, and the heat studies a single dose before exercise. At supplement amounts, splitting has not been tested.^2,6,7

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Sources

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