L-Glutamine: morning or night?

Either, but the two most-studied patterns are post-workout and pre-bed. Post-workout dosing pairs naturally with recovery protocols (often stacked with creatine, whey or essential amino acids, and electrolytes) and may help support immune function during heavy training blocks where exercise-induced glutamine drops have been observed. Pre-bed dosing on an empty stomach is the standard pattern for gut barrier support, the rationale being that an overnight fasted gut benefits from glutamine as enterocyte fuel during the longest daily fasting window. Neither slot is strongly superior in trials; pick what fits your routine.

L-Glutamine is the most abundant free amino acid in human plasma and skeletal muscle, accounting for roughly 60 percent of intramuscular free amino acid pool. It serves as the preferred fuel for enterocytes (intestinal lining cells) and lymphocytes, a nitrogen donor for nucleotide synthesis, a precursor for glutathione, and an intermediate in glucose and ammonia metabolism. Under normal conditions the body synthesises glutamine in adequate amounts from glutamate and ammonia, mainly in skeletal muscle, the liver, and the lungs, which is why glutamine is classified as a 'conditionally essential' amino acid: not essential in health, but essential in catabolic stress (severe burns, major surgery, sepsis, prolonged fasting, intense endurance exercise). For supplementation, timing is flexible. The two most common slots are post-workout (5 grams for recovery and immune support during heavy training blocks) and pre-bed (5 grams on an empty stomach for gut barrier and overnight repair). Single oral doses up to 20 to 30 grams are well-tolerated, but most evidence in healthy adults uses 5 grams two to three times per day. Effects build over weeks; this is not an acute supplement.

The windows above are anchored to a conventional day, not to clock time. If you work nights or wake at midday, shift the whole pattern rather than the individual dose: treat your own waking hour as "morning" and your own wind-down hour as "night". For L-Glutamine the thing that matters is the relationship to your sleep and to your meals, not the number on the clock. Shift workers rotating between days and nights get the most consistent results by anchoring the dose to a fixed event, the first meal of a shift, rather than to a fixed time.

Take it later the same day if there is still a sensible slot left, with water at any point. If the day is gone, skip it and resume tomorrow. Do not double the next dose to compensate: for anything stored in the body a single miss is inconsequential, and for anything cleared quickly a double dose gives no benefit while raising the chance of side effects. Adherence over weeks matters far more than any single perfectly timed dose, which is why the best window for L-Glutamine is usually the one you will actually keep.

• Post-workout or pre-bed

  5g mixed into water on an empty stomach

• Does L-Glutamine actually help leaky gut?+

  It is the preferred fuel for enterocytes (intestinal lining cells) and a substrate for tight junction protein synthesis, so the mechanism is plausible. Trial evidence is strongest in IBD (Crohn's and ulcerative colitis), short bowel syndrome, and post-chemotherapy mucositis at 10 to 30 grams per day under medical supervision. In healthy adults with subclinical 'leaky gut' from stress, NSAIDs, or alcohol, evidence is mixed; 5 grams twice daily on an empty stomach for 4 to 8 weeks is a reasonable trial, but expect modest cumulative effects, not dramatic acute changes.
• Can I take glutamine with creatine?+

  Yes, no known interaction. The post-workout combination of 5 grams creatine monohydrate plus 5 grams L-glutamine plus whey or essential amino acids plus electrolytes is a common stack with no documented adverse effects. Glutamine supports recovery and immune function; creatine supports strength and power. They serve different roles and stack cleanly. Mix together in water or juice.
• Powder or capsules?+

  Powder for almost everyone. Capsules require 5 to 10 pills to hit a 5-gram dose, capsules are more expensive per gram, and the powder mixes cleanly in water with essentially no taste. The only reasons to choose capsules are portability or strong dislike of mixing powders. For higher clinical doses (10 to 30 grams per day), powder is the only practical choice.
• Is L-Glutamine safe long-term?+

  The safety profile in healthy adults at standard supplemental doses (5 to 15 grams per day) is excellent, with decades of use and no consistent adverse effects in trials. Very high doses (30 grams or more daily for years) are less well-studied for long-term safety. People with cirrhosis or significant liver disease should avoid high-dose supplementation because of ammonia generation; people on lactulose for hepatic encephalopathy should not take glutamine; people with active cancer should consult an oncologist.
• Does it matter if I take L-Glutamine at a different time each day?+

  Some variation is fine. A fixed slot is recommended mainly because it is the easiest way to not forget, and because it keeps levels of quickly cleared compounds steadier. Drifting an hour or two either side of your usual time changes very little. Drifting between morning and bedtime is worth avoiding, especially if L-Glutamine affects your sleep or energy.
• Can I take L-Glutamine twice a day instead?+

  Splitting a dose is often better tolerated and, for compounds the body clears quickly, keeps blood levels steadier than one large dose. Do not increase the total by splitting it: divide the daily amount you were already taking. Check the label, some products are formulated as a single daily dose and should not be split.

• Cruzat V, et al. Nutrients. 2018