The amount of magnesium considered "too much" depends largely on whether it comes from food or supplements and on individual health conditions.

• For healthy adults, the recommended dietary allowance (RDA) for magnesium is about 400-420 mg per day for men and 310-320 mg per day for women, with pregnant women needing slightly more

• The tolerable upper intake level (UL) for supplemental magnesium (from pills or medications, not food) is 350 mg per day. Exceeding this amount from supplements increases the risk of adverse effects

• Magnesium overdose or toxicity is rare in healthy individuals because the kidneys efficiently excrete excess magnesium from food. However, high doses from supplements or medications can cause symptoms such as diarrhea, nausea, abdominal cramping, lethargy, and in severe cases, more serious neurological and cardiovascular issues

• Symptoms of magnesium toxicity (hypermagnesemia) include flushing, nausea, vomiting, muscle weakness, loss of reflexes, confusion, low blood pressure, slow heart rate, respiratory depression, and in extreme cases, coma or cardiac arrest

• Magnesium blood levels above about 4.0 mEq/L (approximately 4.8 mg/dL) can cause decreased reflexes; levels above 10-13 mEq/L can cause severe cardiac conduction problems and respiratory failure; levels above 25 mEq/L can lead to cardiac arrest

• People with kidney impairment or certain health conditions are at higher risk of magnesium toxicity because they cannot eliminate excess magnesium efficiently

• If magnesium overdose is suspected, treatment may involve stopping magnesium intake, intravenous calcium to counteract magnesium effects, saline diuresis, and in severe cases, hemodialysis

Summary:

• Up to about 350 mg daily of supplemental magnesium is generally safe for most adults.
• Total magnesium intake from food plus supplements should not cause toxicity in healthy people.
• Taking significantly more than 350 mg supplemental magnesium daily, especially without medical supervision, can lead to toxicity.
• Magnesium toxicity symptoms become more likely with blood magnesium levels above 4 mEq/L and can be life-threatening at very high levels.
• Kidney health is a critical factor in magnesium safety.

Consult a healthcare provider before taking high-dose magnesium supplements, especially if you have kidney problems or other chronic conditions.