Magnesium Bisglycinate (Glycinate) Capsules

Magnesium bisglycinate is the mineral magnesium bound to glycine, an amino acid, in a form sold as a supplement. The prefix "bis" means that each magnesium atom is attached to two glycine molecules. Chemists call this kind of bond a chelate, and this form tends to be gentler on the stomach than other magnesium supplements. Magnesium itself is one of the most plentiful minerals in the body. An adult carries about 25 g of it, half to two thirds held in bone and most of the remainder inside cells. Glycine is a common amino acid found in high-protein foods such as meat and beans, and the body also makes its own.

Sources: Mayo Clinic Press; NIH Office of Dietary Supplements; PubChem, US National Library of Medicine.

Magnesium bisglycinate supplies magnesium, which the body needs for more than 300 enzyme systems. Those enzymes turn food into energy and build protein and DNA. The mineral also moves calcium and potassium across cell membranes, the process behind nerve signals, muscle contraction and a steady heartbeat. Bone contains magnesium as part of its structure, and the parathyroid glands, which regulate calcium, depend on it to work normally. Research on wider effects is mixed. A 2025 trial gave magnesium bisglycinate to 155 adults with poor sleep for four weeks and found a small improvement over placebo, largest in people who ate little magnesium. Trials of magnesium for blood pressure report reductions of only 2 to 4 mmHg. Glycine on its own has been studied for sleep, and 3 g at bedtime improved sleep quality in small trials.

Sources: NIH Office of Dietary Supplements; Food Standards Scotland; peer-reviewed trial, Nature and Science of Sleep, 2025.

Magnesium glycinate and magnesium bisglycinate are the same compound under two names. Chemical databases list glycinate, bisglycinate and diglycinate as one substance, so a product labelled either way contains the same thing. The compound is about one part in seven magnesium by weight: 893 mg of it supplies 125 mg of the mineral. Among other forms, magnesium as aspartate, citrate, lactate or chloride dissolves well and is absorbed more completely than oxide or sulfate. A 1994 trial in 12 patients with impaired absorption found bisglycinate and oxide absorbed to a similar degree overall. Bisglycinate was absorbed faster, was tolerated by every patient, and was absorbed about twice as well as oxide in the four patients with the poorest uptake. Some of the compound appears to pass into the body intact, along the route the gut uses for small peptides.

Sources: PubChem, US National Library of Medicine; NIH Office of Dietary Supplements; peer-reviewed trial (Schuette and colleagues, 1994); peer-reviewed trial, Nature and Science of Sleep, 2025.

Studies of magnesium bisglycinate have used 250 mg of magnesium a day. Clinicians suggest 100 to 200 mg a night as a reasonable starting amount for anyone trying it for sleep. UK guidance puts the daily amount adults need at 300 mg for men and 270 mg for women, counting food and supplements together. The same guidance says that 400 mg or less a day from supplements is unlikely to cause harm. Safety levels elsewhere are lower. The American upper level for supplemental magnesium is 350 mg a day and the European level is 250 mg a day, both set at the point where loose stools begin. Supplement labels state the elemental magnesium rather than the weight of the compound, so 250 mg of magnesium means far more than 250 mg of bisglycinate powder.

Sources: Food Standards Scotland; NIH Office of Dietary Supplements; Cleveland Clinic; EFSA; peer-reviewed trial, Nature and Science of Sleep, 2025.

Magnesium bisglycinate can be taken at any time of day, with no published evidence that one time absorbs better than another. In the 2025 trial, participants took the whole 250 mg dose as two capsules 30 to 60 minutes before bedtime, and the study did not test any other timing. The change measured in that trial appeared within the first 14 days and then held steady. Mayo Clinic advises taking magnesium supplements with meals, because magnesium on an empty stomach can cause diarrhoea. Where a total daily amount is high, the safety studies split it into two or more servings across the day. Around 30% to 40% of the magnesium in food and supplements is absorbed, and unabsorbed magnesium leaves the body in the stool.

Sources: peer-reviewed trial, Nature and Science of Sleep, 2025; Mayo Clinic; NIH Office of Dietary Supplements; EFSA.

Magnesium bisglycinate is commonly taken alongside vitamin D, vitamin B6 and zinc, and research covers each pairing. The body uses magnesium to regulate the active form of vitamin D and parathyroid hormone, so the two are often paired for bone. In a trial of 264 stressed adults, 300 mg of magnesium with 30 mg of vitamin B6 for eight weeks worked no better than magnesium alone overall, but gave a 24% greater improvement in the most severely stressed. Zinc at 142 mg a day, far above any normal supplement, was found to block magnesium absorption. Prescription drugs matter more than other supplements. Magnesium reduces the absorption of oral bisphosphonates and of tetracycline and quinolone antibiotics, so these should be taken at least 2 hours apart. Long-term loop or thiazide diuretics and proton pump inhibitors can lower magnesium levels. Anyone on regular prescriptions should ask a pharmacist first.

Sources: NIH Office of Dietary Supplements; peer-reviewed trial (Pouteau and colleagues, PLOS ONE, 2018).

Magnesium bisglycinate is among the forms of magnesium least likely to upset the stomach, and its side effects are those of magnesium in general. High doses of any magnesium supplement can cause diarrhoea, nausea and stomach cramps, because unabsorbed magnesium draws water into the gut. The forms most often reported to do this are carbonate, chloride, gluconate and oxide. In the 2025 trial of 250 mg a day, 93% of participants reported no side effects, and complaints were fewer on magnesium than on placebo. Excess magnesium from food is not a concern, because healthy kidneys remove it. Very large doses from laxatives or antacids, typically more than 5 g a day, have caused poisoning. The risk rises sharply when kidney function is reduced, so anyone with a kidney problem needs advice first. Anyone pregnant or breastfeeding should speak to a GP or pharmacist first.

Sources: NIH Office of Dietary Supplements; Mayo Clinic Press; peer-reviewed trial, Nature and Science of Sleep, 2025.

Magnesium bisglycinate is not found in food; it is made by combining magnesium with glycine, so the question that matters is which foods contain magnesium. Green leafy vegetables such as spinach and nuts are the richest sources, and bread, fish, meat and dairy foods are good ones. Pumpkin seeds, chia seeds, almonds, cashews, peanuts, black beans and edamame rank highest per serving in American food tables. In general any food high in fibre provides magnesium. Refining grains strips out the germ and bran and with them most of the magnesium, which is why wholemeal bread and brown rice carry more than white. Tap and bottled water can contribute anything from almost nothing to more than 120 mg a litre, depending on the source.

Sources: Food Standards Scotland; NIH Office of Dietary Supplements.