You just got your blood work back. You’re scanning the metabolic panel, expecting the usual—maybe a slightly high cholesterol or a vitamin D deficiency because, honestly, who gets enough sun? Then you see it. Your magnesium level is flagged. It’s high. Not "I ate too many pumpkin seeds" high, but clinically elevated.
It’s weird. We’re constantly told that everyone is magnesium deficient. We’re told to bathe in Epsom salts and swallow massive pills before bed to sleep better. So, why is my magnesium high when the rest of the world is seemingly starving for it?
Hypermagnesemia. That’s the medical term for it. It is actually quite rare in the general population compared to its opposite, hypomagnesemia. If your kidneys are firing on all cylinders, they are incredibly efficient at dumping extra magnesium into your urine. They don't mess around. But when that system glitches, or when you’re unintentionally flooding your body with more than it can handle, things get complicated fast.
The kidney connection is almost always the culprit
Your kidneys are the bouncers of your bloodstream. Under normal conditions, they regulate magnesium with pinpoint precision. If you consume 400mg of magnesium but your body only needs 100mg, the kidneys simply show the rest the exit.
However, when kidney function drops—specifically when the Glomerular Filtration Rate (GFR) falls below 30 mL/min—the bouncers go on strike. This is the most common reason people find themselves asking why their magnesium is high. In stage 4 or 5 chronic kidney disease (CKD), the body loses its ability to excrete minerals effectively. It’s not just about what you’re eating; it’s about what you can’t get rid of.
Sometimes it isn't even chronic. Acute kidney injury (AKI) from severe dehydration or certain medications can cause a sudden, sharp spike. It's scary. You might feel fine one day and lethargic the next because your mineral balance is tilting. Doctors often look at creatinine and BUN levels alongside magnesium to see if the plumbing is the problem.
The over-the-counter trap
Let's talk about the medicine cabinet. You’d be surprised how many common products are secretly magnesium bombs. Take antacids. If you’re dealing with chronic heartburn and popping Mylanta or Maalox like they’re candy, you are ingesting massive doses of magnesium hydroxide.
Then there are the laxatives. Milk of Magnesia isn't just a catchy name; it’s a concentrated dose of the mineral designed to pull water into the intestines. For someone with even mildly impaired kidney function, using these regularly is a recipe for hypermagnesemia. People often don't think of "stomach meds" as something that could mess with their blood chemistry, but they absolutely do.
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Supplements are the other big one. The wellness industry has pushed magnesium as a cure-all for anxiety, leg cramps, and insomnia. While it helps many, the "more is better" mentality is dangerous here. If you're stacking a multivitamin with a ZMA supplement for the gym and a magnesium citrate powder for sleep, you might be hitting 800mg to 1000mg a day. That's a lot for your body to process.
Rare conditions and the "invisible" causes
Sometimes the reason isn't what you're putting in your mouth. It's how your cells are behaving.
Take lithium therapy, for example. Patients treated for bipolar disorder often see a slight uptick in magnesium levels. Lithium can decrease the excretion of magnesium, keeping it in the loop longer than intended. It's a known side effect that psychiatrists monitor, but it can catch a general practitioner off guard if they aren't looking at the whole medication list.
Then there's the truly "out there" stuff like adrenal insufficiency or Addison’s disease. When your adrenal glands aren't producing enough cortisol and aldosterone, your mineral balance goes haywire. Aldosterone usually helps regulate sodium and potassium, but its absence creates a cascade effect that can keep magnesium levels higher than normal.
Other niche causes include:
- Hypothyroidism: A sluggish thyroid slows down everything, including the rate at which your kidneys clear minerals.
- Milk-Alkali Syndrome: This usually happens when people take too much calcium carbonate (like Tums) along with milk. It creates a metabolic environment where magnesium levels can climb.
- Theophyllines: Certain asthma medications have been linked to shifts in magnesium.
- Rhabdomyolysis: When muscle tissue breaks down rapidly due to extreme exercise or injury, the cells burst and dump their internal magnesium into the blood.
What does high magnesium actually feel like?
Early on? Probably nothing. You might just feel a bit "off." But as the numbers climb, the symptoms become more distinct and, frankly, a bit unsettling.
First, you might notice your blood pressure dropping. You feel dizzy when you stand up. Then comes the nausea. It’s not a "food poisoning" nausea; it’s a heavy, systemic feeling of malaise. Because magnesium acts as a natural calcium channel blocker and a muscle relaxant, too much of it makes your muscles too relaxed.
Doctors check your "deep tendon reflexes." If they tap your knee with that little rubber hammer and nothing happens—or the response is very weak—that’s a classic sign of hypermagnesemia. Your nerves aren't communicating with your muscles effectively. In severe cases, this leads to muscle weakness or even respiratory paralysis because the muscles that help you breathe just... stop trying.
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The heart is the biggest concern. Magnesium affects the electrical conductivity of the heart. On an EKG, a doctor might see a prolonged PR interval or a widened QRS complex. If levels get high enough, the heart can actually stop. It sounds dramatic because it is.
Interpreting the numbers: What is "normal"?
A typical reference range for serum magnesium is 1.7 to 2.2 mg/dL (0.85 to 1.10 mmol/L).
If you're at 2.5, your doctor might just tell you to stop taking your supplements. If you're at 4.0, they’re going to start looking at your kidney function very closely. If you're above 7.0, you're likely in a hospital setting getting intravenous calcium to protect your heart.
It's important to note that serum magnesium—the stuff they measure in a standard blood test—only represents about 1% of the total magnesium in your body. The rest is tucked away in your bones and soft tissues. This means that if your blood levels are high, your body's storage tanks are likely overflowing.
Myths about high magnesium
One big misconception is that eating too many spinach salads or almonds will give you hypermagnesemia. For a healthy person, this is virtually impossible. Your body is too smart for that. You would get diarrhea long before your blood levels reached a dangerous point because the intestines have a built-in "limit" for absorption from food sources.
Another myth is that Epsom salt baths are dangerous. While your skin does absorb some magnesium, the amount is negligible compared to oral ingestion. Unless you are soaking in a tub for eight hours a day while having kidney failure, the bath isn't the reason your labs are high.
Real-world next steps
If you are staring at a lab report and wondering why is my magnesium high, don't panic, but do take it seriously. It is a biological signal that something is out of balance.
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1. Audit your intake immediately. Look at every single label in your medicine cabinet. Check for "Magnesium Stearate" (usually just a filler, but still), "Magnesium Citrate," "Magnesium Oxide," or "Magnesium Sulfate." Stop any supplements until you talk to your doctor.
2. Re-test for accuracy.
Lab errors happen. Hemolysis—which is when red blood cells burst during the blood draw or while the sample is being handled—can cause a "pseudohypermagnesemia." Since red blood cells contain much more magnesium than the plasma around them, if they break, they leak that magnesium into the sample, making your levels look artificially high. Ask for a re-test to be sure the result is real.
3. Request a full renal panel.
If the high magnesium is real, you need to know how your kidneys are doing. Check your GFR and Creatinine. If those are normal, the cause is almost certainly exogenous (meaning it's something you're eating or taking).
4. Hydrate.
If your kidneys are healthy, drinking plenty of water helps them flush out the excess mineral. Just don't overdo it to the point of hyponatremia (low sodium). Moderation is key.
5. Check your Calcium levels.
Calcium and Magnesium have an antagonistic relationship. Sometimes high magnesium is a symptom of a broader electrolyte imbalance involving calcium or potassium.
In clinical settings, doctors might use diuretics like Furosemide (Lasix) to force the kidneys to dump magnesium, or in extreme cases, they use dialysis to mechanically filter the blood. For most people, though, simply identifying the hidden source in their diet or medication is enough to bring the numbers back to earth. Pay attention to the subtle signs your body gives you—the fatigue, the slow reflexes, the "brain fog" that feels more like a physical sedation. Your chemistry is a delicate balance, and sometimes, the best thing you can do for your health is to stop "optimizing" and just let your body recalibrate.