Magnesium Citrate

Why can a supplement loosen stools?

High supplemental magnesium intakes can cause diarrhea, nausea and abdominal cramping. For a constipation medicine, stool loosening is the intended action; in a nutritional supplement, the same effect may be unwanted. Kidney impairment increases the risk of magnesium accumulating to toxic levels. 1 2

Why do German and US limits differ?

BfR recommends a maximum of 250 mg magnesium in a supplement’s daily portion, divided into at least two intakes. Its assessment discusses the European upper level of 250 mg from readily dissociable supplemental and added magnesium, excluding magnesium naturally present in foods. The limits were based mainly on diarrhea. 3

The US adult upper limit is 350 mg daily from supplements and medicines, also excluding food magnesium. These limits concern routine unsupervised intake; research doses and medicinal laxative regimens can be different and should not be mistaken for everyday supplement targets. 1 2

Which medicines need a closer look?

Magnesium can reduce absorption of tetracycline and quinolone antibiotics and oral bisphosphonates. NIH describes taking those antibiotics at least two hours before or four to six hours after magnesium, and separating oral bisphosphonates by at least two hours. The actual medicine’s instructions remain important. 1

Diuretics can change magnesium losses, while long-term proton-pump inhibitor use can cause low magnesium. These are reasons to review the whole medication list rather than interpreting a supplement in isolation. 1

When is constipation a reason for medical advice?

MedlinePlus advises discussing magnesium citrate with a clinician when there is kidney disease, abdominal pain, nausea or vomiting, a sudden bowel-habit change lasting more than two weeks, or pregnancy or breastfeeding. Rectal bleeding or failure to pass stool after use calls for stopping the medicine and contacting a clinician. 2