Quick answer

NIH's LactMed database says a breastfed infant absorbs magnesium poorly, so a mother's magnesium is not expected to change the infant's blood level. The entries found cover citrate, oxide, hydroxide and aspartate, not glycinate. NIH lists a 350 mg upper limit for supplements. Ask your doctor about your own situation.^1,2

Key facts

LactMed's entries for magnesium citrate, oxide and aspartate say oral absorption of magnesium by the infant is poor, and that intravenous magnesium raises milk magnesium only slightly.^1,3,4
Searches of LactMed in October 2026 found entries for magnesium citrate, oxide, hydroxide, aspartate and sulfate, and none for glycinate, malate or threonate.⁵
In a study of 40 matched pairs of women, magnesium aspartate for at least 4 weeks before delivery went with fewer women exclusively breastfeeding at discharge, 63% against 80%.⁴
NIH's upper limit for supplemental magnesium is 350 mg a day for breastfeeding women aged 14 to 50.²
Over-the-counter magnesium labels tell breastfeeding users to ask a health professional or doctor before use.^6,7

What LactMed says about magnesium and breast milk

LactMed is the National Library of Medicine's database of drugs and other substances that breastfeeding mothers may be exposed to. Its magnesium citrate entry says no clinical information is available on citrate during breastfeeding, so it draws on other magnesium salts that have been studied.¹

From those salts it reports that intravenous magnesium raises milk magnesium only slightly and that infants absorb little magnesium by mouth. It concludes that a mother's magnesium is not expected to affect the breastfed infant's serum magnesium, and it says no special precautions are required. The oxide and aspartate entries give the same summary.^1,3,4

The one study of infants it describes involved 50 mothers in their first day after birth, who received mineral oil or an emulsion of mineral oil and magnesium hydroxide equal to 900 mg of magnesium hydroxide. No infant had markedly abnormal stools, but every infant also received supplemental feedings, and the entry does not say how many mothers took each product.⁸

Which forms LactMed covers, and which it does not

The entries cover the forms sold as antacids, laxatives and some supplements: citrate, oxide, hydroxide and aspartate, plus intravenous sulfate. Searches of the database in October 2026 found no entry for magnesium glycinate or other forms, so the sources checked do not address them. That is not a finding either way, so ask your doctor or pharmacist about the form you use.^5,9

Several of the covered forms are also sold as laxatives. The label on a magnesium citrate laxative says a breastfeeding user should ask a health professional before use, and the label on a magnesium oxide antacid lists breastfeeding among the reasons to ask a doctor first.^6,7

Magnesium and the start of lactation

LactMed's entries add one caution that comes from pregnancy rather than from breast milk: magnesium supplements taken during pregnancy might delay the onset of lactation. The entries describe a matched study of 40 pairs of women. Those taking magnesium aspartate, about 459 mg of magnesium a day on average, for at least 4 weeks before delivery were less often exclusively breastfeeding at discharge than women who took none (63% against 80%).^1,4

A separate group of findings concerns magnesium sulfate given by vein in hospital to women with severe pre-eclampsia. In randomized trials, a 24-hour infusion after birth delayed the onset of lactation compared with a shorter one. That is a different treatment from a supplement.⁹

What NIH lists for breastfeeding women

NIH's recommended amount of magnesium while breastfeeding is 360 mg a day for teens, 310 mg at ages 19 to 30 and 320 mg at ages 31 to 50, counting food, drinks, supplements and medicines together. The upper limit is 350 mg a day for supplements and medicines alone.²

The upper limit for magnesium from supplements and medicines is 350 mg a day for adults. It does not count magnesium in food and drinks.^2,10

Who should ask their doctor

NIH advises caution with supplements beyond a standard prenatal supplement while nursing, because many have not been well tested in nursing women. Ask your doctor, midwife or a lactation consultant before starting a magnesium supplement if you have kidney disease, take antibiotics, a bisphosphonate, a diuretic or an acid reflux medicine, or are already using a magnesium laxative or antacid.^2,11

Questions people ask

Is magnesium ok while breastfeeding?

LactMed's summary for the salts it covers does not call for special precautions, because infants absorb little magnesium. Labels still say to ask a health professional, so ask your doctor about your own supplement.^1,6

Is magnesium safe while nursing?

LactMed says a mother's magnesium is not expected to change the nursing infant's blood magnesium. It also notes that supplements taken during pregnancy might delay the onset of lactation, so mention any supplement to your doctor.^1,4

Is magnesium glycinate safe while breastfeeding?

Searches of LactMed found no entry for magnesium glycinate, and the other sources checked do not address it. That is not a finding either way, so ask your doctor or pharmacist.⁵

Is magnesium citrate safe while breastfeeding?

LactMed has a magnesium citrate entry. It says there is no clinical information on citrate itself, bases its summary on other magnesium salts, and says no special precautions are required. The laxative label tells breastfeeding users to ask a health professional first.^1,6

Is taking magnesium safe while breastfeeding if I use it every day?

The sources checked do not separate daily from occasional use. NIH's upper limit of 350 mg a day applies to supplements and medicines while breastfeeding, so ask your doctor to look at everything you take.²

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