High magnesium in the blood is called hypermagnesemia.
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The 10 main signs are:
- Nausea
- Vomiting
- Facial flushing or warmth
- Low blood pressure
- Muscle weakness
- Drowsiness or unusual lethargy
- Confusion or dizziness
- Reduced or absent reflexes
- Slow or shallow breathing
- Slow or irregular heartbeat
Severe hypermagnesemia can cause paralysis, heart block, coma, cardiac arrest and death. A serum magnesium blood test is needed to confirm the condition because these symptoms can also occur with other medical problems.
The 10 Signs of High Magnesium Explained
| Sign | What it may feel or look like |
|---|---|
| 1. Nausea | Feeling sick, sometimes with stomach discomfort |
| 2. Vomiting | Repeated vomiting, particularly after taking a magnesium-containing product |
| 3. Facial flushing or warmth | Warm, red or flushed skin, especially on the face |
| 4. Low blood pressure | Light-headedness, weakness or fainting |
| 5. Muscle weakness | Heavy limbs, difficulty standing or reduced muscle strength |
| 6. Drowsiness or lethargy | Unusual sleepiness, slowed responses or difficulty staying awake |
| 7. Confusion or dizziness | Trouble thinking clearly, disorientation or loss of balance |
| 8. Reduced reflexes | Diminished knee or other tendon reflexes, usually detected by a clinician |
| 9. Slow or shallow breathing | Breathing that becomes unusually slow, weak or difficult |
| 10. Slow or irregular heartbeat | A low pulse, palpitations or an abnormal heart rhythm |
Symptoms often become more serious as the blood magnesium level rises. Early or moderate toxicity may cause nausea, weakness, dizziness, confusion, facial flushing and low blood pressure. Higher levels can suppress nerve and muscle function, slow breathing and interfere with the heart's electrical conduction.
When Is High Magnesium an Emergency?
High magnesium requires emergency medical help when it causes breathing changes, severe weakness, reduced alertness, very low blood pressure or an abnormal heart rhythm.
Seek emergency help for:
- Slow, shallow or difficult breathing
- Fainting or very low blood pressure
- Severe weakness or difficulty moving normally
- Extreme drowsiness, inability to wake up or confusion
- A slow or irregular heartbeat
- Loss of consciousness
- A suspected overdose of magnesium laxatives, antacids or supplements
Severe hypermagnesemia can lead to muscle paralysis, dangerously slow heart rhythms, heart block, coma and cardiac arrest.
If someone in the United States may have taken too much magnesium, contact Poison Help at 1-800-222-1222. Call 911 for breathing problems, collapse, severe drowsiness or an abnormal heartbeat. Do not induce vomiting unless a poison specialist or healthcare professional tells you to.
What Causes High Magnesium?
High magnesium is uncommon in people with healthy kidneys because the kidneys usually remove excess magnesium in urine.
Common causes include:
- Kidney failure or substantially reduced kidney function
- Excessive use of magnesium supplements
- Magnesium-containing laxatives, such as milk of magnesia
- Magnesium-containing antacids
- Intravenous magnesium treatment
- Certain medical conditions, including hypothyroidism or adrenal insufficiency
- Some medicines, including lithium, in specific circumstances
The risk is higher when someone with impaired kidney function takes a usual dose of a magnesium-containing laxative, antacid or supplement.
Can Diarrhea Mean You Have High Magnesium?
Diarrhea after taking a magnesium supplement does not necessarily mean that you have high blood magnesium.
Magnesium salts draw water into the intestine and commonly cause diarrhea, abdominal cramping and nausea. These effects can occur without dangerous hypermagnesemia.
Diarrhea can still indicate that the dose is too high. The risk of toxicity is higher in people with kidney disease. Persistent symptoms, severe weakness, confusion or breathing changes require medical evaluation.
How Is High Magnesium Diagnosed?
A healthcare professional usually confirms hypermagnesemia with a serum magnesium blood test.
The evaluation may also include:
- Kidney-function tests
- Calcium and potassium levels
- Blood pressure measurement
- An electrocardiogram if symptoms affect the heart
Symptoms alone cannot reliably distinguish high magnesium from low magnesium, medication effects or other electrolyte problems.
What to Remember
High magnesium is most concerning when muscle weakness, reduced alertness, low blood pressure, breathing changes or an abnormal heartbeat occur after magnesium exposure, especially in someone with kidney disease. Symptoms can raise concern, but a serum magnesium blood test is needed to confirm the diagnosis.