Magnesium glycinate (magnesium bisglycinate) is elemental magnesium bound to two molecules of the amino acid glycine. The chelate is well tolerated and the least likely magnesium form to cause loose stools, which is why it’s the usual choice for people taking magnesium for calm or sleep, or for anyone who gets diarrhea on cheaper salts. For the mineral’s full evidence base — blood pressure, blood sugar, migraine and more — see Magnesium; this page covers what’s specific to the glycinate form.
Absorption & Tolerability
As an organic chelate, glycinate is well absorbed and notably gentle on the gut. The practical advantage over inorganic salts is tolerability more than dramatically higher absorption — among common forms, only magnesium oxide is clearly a poor absorber (fractional absorption ~4% in a human comparison), while other salts, inorganic and organic alike, are broadly equivalent 1Reference 1Clinical trialBioavailability of US commercial magnesium preparations — [comparative human study]View study →. A stable-isotope crossover trial in patients with ileal resection found magnesium diglycinate and magnesium oxide were absorbed similarly overall (23.5% vs 22.8%), but the chelate was absorbed better in the four patients with the worst malabsorption (23.5% vs 11.8%) and was better tolerated by everyone — evidence that part of the dose is taken up intact as a dipeptide in the proximal small intestine 2Reference 2RCTBioavailability of magnesium diglycinate vs magnesium oxide in patients with ileal resection — [randomised crossover trial]View study →.
Its elemental magnesium is only about 14% by weight, so a meaningful dose means comparatively large capsules — check the elemental figure on the label, not the total compound weight. (Products labelled “buffered bisglycinate” mix in magnesium oxide to raise the elemental percentage, which also reduces the tolerability edge.) The bound glycine is itself mildly calming — glycine taken before bed has been reported to improve subjective sleep quality, plausibly by lowering core body temperature — which may add to the form’s “relaxation” reputation 3Reference 3ReviewNew therapeutic strategy for amino acid medicine: glycine improves the quality of sleep — [review]View study →.
What the Evidence Says
Most magnesium trials used other salts, so glycinate-specific clinical data are limited. The main direct trial is a 2025 randomised, double-blind, placebo-controlled study in 155 healthy adults reporting poor sleep: 250 mg elemental magnesium as bisglycinate daily for 4 weeks produced a statistically significant but small improvement in insomnia severity versus placebo (Insomnia Severity Index −3.9 vs −2.3; p = 0.049; Cohen’s d ≈ 0.2), with a larger effect in participants who had lower baseline dietary magnesium 4Reference 4RCTMagnesium bisglycinate supplementation in healthy adults reporting poor sleep: a randomised, placebo-controlled trial — [RCT]View study →. That is consistent with the broader, modest sleep evidence for magnesium (see Magnesium) and reads partly as deficiency correction rather than a general sedative effect. The trial was academic (Leibniz University Hannover; Murdoch University) and DRKS-registered, but one co-author declared an industry conflict of interest — worth noting for a positive result this small.
Choose glycinate for tolerability and comfort, not because it has uniquely strong outcome data.
Gap: there is little head-to-head evidence that glycinate outperforms other well-absorbed forms on any clinical outcome; its edge is gentleness, not proven superiority, and the one direct sleep trial shows only a small effect from a study with an industry-linked co-author.
Dosage
Common supplemental doses are 120–240 mg of elemental magnesium, often taken in the evening; split higher intakes across the day, since fractional absorption falls as the single dose rises. These are ranges used in research and common practice, not a personal recommendation — see the dosing and upper-limit notes on Magnesium. Remember the label caveat: “250 mg magnesium bisglycinate” is roughly 35 mg elemental magnesium unless the label states the elemental amount.
Safety
Very well tolerated — the least laxative magnesium form, so the usual dose-limiting side effect (osmotic diarrhea) is least likely here. The general magnesium cautions still apply: people with kidney impairment should not supplement without medical advice (impaired renal clearance is the main route to hypermagnesemia), and magnesium should be separated by ≥2 hours from oral bisphosphonates and certain antibiotics (tetracyclines, fluoroquinolones), which it can chelate and block in the gut (see Magnesium).
Pregnancy & lactation
Magnesium is commonly used in pregnancy and the glycinate form adds no known form-specific risk, but supplemental use should be individualised with a clinician — dose and need depend on diet and status. This form page does not add a pregnancy assessment beyond the hub; see Magnesium.
Scope of this safety review (for honesty, not a claim):
- Interactions assessed? Yes — the two clinically important classes for oral magnesium (bisphosphonates; tetracycline/fluoroquinolone antibiotics) plus the renal-clearance caution; these are form-agnostic and detailed on the hub.
- Pregnancy/lactation assessed? Partially — no glycinate-specific risk identified; deferred to the magnesium hub for the full assessment.
- Upper Limit? Yes, but it belongs to the mineral, not the form: the IOM tolerable upper intake level for supplemental magnesium is 350 mg/day of elemental magnesium (it does not count magnesium from food). Given on the Magnesium hub.
References
- Firoz, M., & Graber, M. (2001). Bioavailability of US commercial magnesium preparations — [comparative human study]. Magnesium Research. https://pubmed.ncbi.nlm.nih.gov/11794633/
- Schuette, S. A., Lashner, B. A., & Janghorbani, M. (1994). Bioavailability of magnesium diglycinate vs magnesium oxide in patients with ileal resection — [randomised crossover trial]. JPEN Journal of Parenteral and Enteral Nutrition. https://pubmed.ncbi.nlm.nih.gov/7815675/
- Bannai, M., & Kawai, N. (2012). New therapeutic strategy for amino acid medicine: glycine improves the quality of sleep — [review]. Journal of Pharmacological Sciences. https://pubmed.ncbi.nlm.nih.gov/22293292/
- Schuster, J., Cycelskij, I., Lopresti, A., & Hahn, A. (2025). Magnesium bisglycinate supplementation in healthy adults reporting poor sleep: a randomised, placebo-controlled trial — [RCT]. Nature and Science of Sleep. https://pubmed.ncbi.nlm.nih.gov/40918053/