Too much magnesium? Overdose symptoms and what to do

Worried you took too much magnesium? Most of the time, excess shows up as dose‑related digestive symptoms (laxative effect), especially with certain forms and at high single doses. More rarely—particularly with impaired renal function—true hypermagnesemia can appear with neurological and cardiovascular signs.

When is it “too much magnesium”?

In healthy adults, kidneys usually regulate magnesium well. Excess is more likely if you combine high‑dose supplements, magnesium‑containing laxatives/antacids, or have renal insufficiency.

• Recommended daily intakes are around 300–380 mg/day depending on sex; see ANSES intake references.
• For GI prudence, EFSA proposes a tolerable upper limit from supplements only (to avoid diarrhea) — see EFSA’s UL for supplemental magnesium.

In practice, food rarely causes trouble; over‑dosed supplements or poor dose splitting do.

Common symptoms of excess

Typically mild, dose‑dependent, and reversible by stopping or lowering dose:

• Diarrhea, loose stools, abdominal cramps, bloating
• Nausea, sometimes vomiting, metallic taste
• Fatigue, a sense of weakness or heaviness
• Flushing, blood pressure drops in sensitive individuals

These reflect digestive excess from magnesium salts (osmotic effect) and usually subside quickly after dose reduction.

Red flags for hypermagnesemia (rarer)

More likely with reduced kidney function or very high intakes (IV, magnesium‑rich laxatives):

• Unusual drowsiness, confusion, reduced reflexes
• Bradycardia, marked hypotension, palpitations or arrhythmias
• Significant muscle weakness, a “paralysis” feeling, breathing difficulty

If present, seek urgent care. Diagnosis relies on serum magnesium with electrolytes; see hypermagnesemia for clinical details.

Frequent causes of excess

• High‑dose supplements (often > 400–500 mg/day of elemental magnesium), especially if not split
• Magnesium‑containing laxatives/antacids used long‑term
• Renal insufficiency (reduced elimination)
• Stacking multiple magnesium‑containing products (e.g., powder + antacid)
• Intravenous administration (hospital setting)

What to do if you took too much

1. Pause the supplement and hydrate
2. When symptoms resolve, restart lower and split (AM/PM)
3. Prefer better‑tolerated forms (e.g., bisglycinate, malate) and avoid very large single doses
4. If you have kidney disease or sensitive medications, get medical advice first
5. With red‑flag symptoms, seek urgent care

Why some forms “pass” better than others

The laxative effect depends on dose and form. Salts with higher osmotic effect (e.g., citrate, oxide, chloride) can speed transit at high dose. Many people do better with bisglycinate (for the same elemental dose) and splitting intakes.

If diarrhea occurs:

• Reduce the daily dose
• Split (AM/PM) and take with meals
• Trial a different form

Prevention: four simple reflexes

• Check dietary intake first (nuts, seeds, legumes, whole grains, greens) — see practical pointers in the magnesium guide
• Choose a reasonable dose (often 200–400 mg/day elemental), tailored to your context
• Split doses and avoid stacking supplements + magnesium laxatives/antacids without oversight
• Review concomitant meds and separate if interactions are possible

Sources

• EFSA — reference values and UL for supplemental magnesium
• ANSES — magnesium intake references
• MedlinePlus — serum magnesium test
• Merck Manual Professional — hypermagnesemia: signs and management
• NIH ODS — magnesium interactions and tolerance