What are signs of too much magnesium?

The first column, gut signs that mean a surplus and a smaller dose

The signs of too much magnesium sort into two columns, and the column decides the action. The first column is the gut, and its signs mean a surplus and a smaller dose: loose stools, the earliest and commonest, arriving within hours of a dose that exceeded what the gut absorbed, unabsorbed magnesium drawing water into the bowel; diarrhoea, the same effect at volume; nausea, sometimes from a fasted dose rather than a large one, fixed by food; and abdominal cramping or bloating from the osmotic load. These signs are dose-dependent and salt-dependent, oxide and citrate producing them at lower doses than bisglycinate because they are less absorbed, and they are self-limiting, the surplus leaving in the stool and the kidneys excreting what was absorbed, so the action is to reduce the dose, change to a better-absorbed salt, take it with food or split it across two meals, and to count the hidden magnesium in antacids, laxatives and multivitamins that may have pushed the total past the 400mg supplemental guidance level without the reader noticing, the not-with page's fourth list. A healthy adult on a supplement habit meets the first column at most, and a bisglycinate reader at 300mg elemental rarely meets it at all, the first column being the body's own dose limit rather than a danger.

The second column, systemic signs that mean hypermagnesaemia and urgent help, and who it actually happens to

The second column is systemic, and its signs mean a raised blood magnesium, hypermagnesaemia, and urgent help rather than a smaller dose: unusual lethargy and drowsiness; muscle weakness and loss of reflexes; facial flushing and a feeling of warmth; low blood pressure with dizziness or faintness; a slow or irregular pulse; confusion; and, at the extreme, breathlessness from weakened breathing muscles, the sequence the hypermagnesaemia literature describes as serum magnesium climbs, with cardiac arrest the end of it. Those signs are an emergency, and the person showing them, or the person with them, calls for urgent medical help and says what magnesium has been taken, the treatment being intravenous calcium to counter the effects on heart and muscle and, where the kidneys cannot clear the load, dialysis. Who the second column actually happens to is the triage that keeps the page honest: normal kidneys excrete surplus magnesium efficiently, so hypermagnesaemia in the literature occurs almost entirely in people with impaired kidney function taking any magnesium, including magnesium antacids and laxatives that seem harmless, and in massive ingestions of magnesium laxatives or Epsom salts, grams at a time, with a healthy adult on labelled supplement doses not among the cases. The two columns filed: gut signs mean reduce, and they are what a surplus capsule dose produces; systemic signs mean seek help, and they belong to kidney disease and laxative-scale intake; a reader with kidney disease treats the first column as a warning sign of the second and every magnesium product as a doctor's question; and the worked example stays in the first column at most, bisglycinate at 300mg elemental under the level, £19.99 for 90 days at 22p, the salt and the dose that rarely produce a sign of anything.

The verdict, two columns and a triage

What are the signs of too much magnesium: gut signs, loose stools, diarrhoea, nausea and cramping, which mean a surplus dose and a smaller one, and systemic signs, lethargy, muscle weakness, flushing, low blood pressure, a slow pulse, confusion or breathlessness, which mean hypermagnesaemia and urgent help, the second column happening almost only to people with impaired kidneys or massive intake from laxatives and antacids and never to a healthy adult on a labelled supplement dose. The dose that stays in the first column at most: Futuro Labs Magnesium Glycinate, bisglycinate, 300mg elemental at 80% NRV, £19.99 for 90 days at 22p a day.

What to check on the label

Questions people also ask

What are the first signs of taking too much magnesium?

Gut signs: loose stools within hours, then diarrhoea, nausea and abdominal cramping, the osmotic effect of unabsorbed magnesium, which mean the dose exceeded what the gut absorbed and a smaller dose, a better salt or food fixes it.

What are the symptoms of too much magnesium in adults that need a doctor?

Systemic signs: unusual lethargy, muscle weakness and lost reflexes, flushing, low blood pressure with faintness, a slow or irregular pulse, confusion or breathlessness, which mean hypermagnesaemia and urgent medical help.

Can a healthy person get magnesium toxicity from supplements?

Almost never: normal kidneys excrete surplus magnesium efficiently, and the cases of hypermagnesaemia in the literature involve impaired kidney function or massive intake from magnesium laxatives, Epsom salts and antacids.

What are the signs of too much magnesium glycinate specifically?

The same gut signs as any salt, reached later because bisglycinate is best absorbed and least laxative, so a bisglycinate reader's too much is a loose-stool morning rather than anything in the systemic column.

What should someone with kidney disease watch for?

Any sign at all: with impaired excretion the gut signs can precede hypermagnesaemia, so every magnesium product, including antacids and laxatives, is a doctor's question and any systemic sign is an emergency.

Sources

1. The hypermagnesaemia literature: raised serum magnesium is rare with normal kidney function and occurs with impaired excretion or massive intake from magnesium laxatives and antacids, presenting with nausea, lethargy, low blood pressure, muscle weakness and slowed heart conduction, and treated in hospital with intravenous calcium and, where needed, dialysis. PubMed record
2. The hypermagnesaemia literature: the kidneys excrete surplus magnesium, so supplementation is safe for healthy adults within guidance and warrants medical advice in chronic kidney disease, where impaired excretion allows magnesium to accumulate. PubMed record
3. Expert Group on Vitamins and Minerals. Safe Upper Levels for Vitamins and Minerals. Food Standards Agency, 2003 (magnesium guidance level 400mg a day from supplements). https://cot.food.gov.uk/sites/default/files/vitmin2003.pdf
4. The magnesium and medicines literature: magnesium supplements reduce absorption of tetracycline and quinolone antibiotics, bisphosphonates and levothyroxine when taken together and are spaced from them, while proton-pump inhibitors and some diuretics lower magnesium status, a reason for medical advice in either direction. PubMed record

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