Everyone is obsessed with magnesium right now. It’s in every TikTok "sleep cocktail" and every wellness influencer’s morning routine. We’re told we are all deficient, that our soil is depleted, and that we need more, more, more to fix our anxiety and leg cramps. But honestly? You can actually have too much of a good thing. It's called hypermagnesemia. While your kidneys are usually rockstars at filtering out the extra stuff you get from food, supplements and certain medications change the game entirely. If you've been popping magnesium glycinate like candy or overdoing the Epsom salt baths, you might start noticing some weird shifts in how you feel. Symptoms of excess magnesium aren't always dramatic at first, but they can get dangerous fast if you don't know what to look for.
It's rare for a healthy person to get toxic levels of magnesium just from eating too much spinach or almonds. Your body is smarter than that. The real trouble usually starts with high-dose supplements or "osmotic" laxatives like Milk of Magnesia.
The first signs things are heading south
The gut is usually the first place you’ll feel it. Magnesium draws water into the intestines. It’s why people use it for constipation. But when you overdo it, that "helpful" effect turns into a disaster. You’re looking at diarrhea that feels urgent and cramping that just won't quit. Some people describe it as a dull, heavy ache in the lower abdomen. It's basically your body’s emergency exit strategy to get the excess mineral out of your system as quickly as possible.
Then there’s the nausea. It isn't always the "I’m going to throw up" kind of nausea. Sometimes it's just a general sense of malaise or a loss of appetite. You might feel "off" or slightly green around the gills after taking your vitamins. If you're pairing your supplements with antacids that also contain magnesium—think Rolaids or Mylanta—you’re doubling down on the dose without even realizing it.
Why your blood pressure might take a dive
One of the more clinical symptoms of excess magnesium is hypotension. That’s just a fancy way of saying low blood pressure. Magnesium is a natural calcium antagonist; it helps your blood vessels relax. In the right amounts, that’s great for heart health. In massive amounts? Your blood pressure can drop to levels that make you feel dizzy or lightheaded when you stand up too fast.
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You might feel a weird warmth spreading through your skin. This is "flushing." It happens because those peripheral blood vessels are dilating too much. It’s not a sunburn, and it’s not an allergy. It’s just your vascular system reacting to a mineral overload. If you notice your face getting red and your head feeling "swimmy" shortly after taking a supplement, that is a massive red flag.
When symptoms of excess magnesium get serious
When magnesium levels in the blood (serum magnesium) climb above a certain point—usually around 1.74 to 2.61 mmol/L—things move from "uncomfortable" to "scary." You might start feeling incredibly lethargic. Not just "I didn't sleep well" tired, but a heavy, soul-crushing fatigue where moving your limbs feels like walking through waist-high mud.
Your muscles need a very specific balance of calcium and magnesium to contract and relax. When magnesium floods the zone, it blocks the signals that tell your muscles to move. This leads to something called "hyporeflexia." Basically, your reflexes go numb. A doctor tapping your knee with that little rubber hammer would get zero response.
The neurological fog
Confusion is a big one. People often mistake it for "brain fog" or just getting older. But acute magnesium toxicity can make you feel genuinely disoriented. You might forget what you were doing mid-task or struggle to find basic words. It’s a sedative effect. Since magnesium is often marketed as a relaxation aid, people sometimes think this "relaxed" feeling is the supplement working. It isn't. If you feel like you've been drugged, you've likely crossed the line into toxicity.
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Who is actually at risk?
Most of us have kidneys that work overtime to keep us safe. They pee out the extra magnesium before it can cause harm. But if your kidney function is even slightly compromised—which is more common than people think, especially with age or undiagnosed diabetes—you lose that safety net. The National Institutes of Health (NIH) warns that the tolerable upper intake level (UL) for supplemental magnesium is actually quite low: just 350 mg for adults.
Wait. Think about that.
Many "extra strength" supplements on the shelf at the grocery store contain 400 mg or 500 mg in a single pill. That means one pill puts you over the recommended daily limit for supplements. If you’re also eating a magnesium-rich diet, you’re pushing the envelope every single day.
- Kidney issues: This is the number one risk factor. If your filters are clogged, the magnesium stays in the blood.
- Laxative abuse: Older adults often use magnesium-based laxatives daily. This is a recipe for chronic over-accumulation.
- Intravenous (IV) drips: The "Myers' Cocktail" and other wellness IVs can bypass the gut’s natural regulation. If the dose is too high or dripped too fast, it's an immediate system shock.
The "silent" heart complications
This is the part that keeps ER doctors up at night. Because magnesium affects electrical signaling, too much of it can mess with your heart’s rhythm. We’re talking about bradycardia—a dangerously slow heart rate. In extreme cases of hypermagnesemia, the heart can actually stop (cardiac arrest) because the electrical "pacemaker" signals are being dampened by the excess mineral.
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You might feel palpitations or a sensation that your heart is skipping beats. Or, conversely, it might feel like your heart is thumping heavily but slowly. According to research published in the Journal of the American Society of Nephrology, extreme hypermagnesemia is a clinical emergency that often requires calcium gluconate to "cancel out" the magnesium effects, or even emergency dialysis to mechanically scrub the blood.
Getting your levels back to normal
If you suspect you're dealing with symptoms of excess magnesium, the very first step is the most obvious: stop the supplements. All of them. Even the multivitamins. You need to give your kidneys a chance to clear the backlog.
Hydration is your best friend here. Drinking plenty of water helps facilitate the filtration process. However, if you’re feeling the more severe symptoms—the extreme lethargy, the slow heart rate, or difficulty breathing (which happens when the respiratory muscles get too relaxed)—you don't wait. You go to the emergency room. They can run a simple blood test to check your serum magnesium levels and see exactly where you stand.
Practical steps for the future
Don't guess, test. If you’re worried about your magnesium levels, ask your doctor for an RBC Magnesium test. It’s generally considered more accurate than a standard serum test because it looks at the magnesium stored in your red blood cells, not just what’s floating in your plasma at that exact second.
- Check your labels: Look for "hidden" magnesium in antacids, laxatives, and "calm" powders.
- Rotate your sources: Try to get your magnesium from pumpkin seeds, almonds, and leafy greens first. The fiber in these foods naturally regulates how much your body absorbs.
- Listen to your gut: If a supplement gives you loose stools every time you take it, your body is literally telling you it can't handle that dose. Lower it or switch forms.
- Monitor kidney health: Ensure your annual physical includes a GFR (Glomerular Filtration Rate) check to make sure your kidneys are fit enough to handle supplementation.
The "more is better" mindset in the supplement world is a dangerous trap. Magnesium is an essential spark plug for over 300 biochemical reactions in your body, but you aren't a machine that needs to be flooded with oil. Aim for balance. If you start feeling unusually slow, flushed, or spend way too much time in the bathroom, put the bottle down. Your body knows what it’s doing; you just have to pay attention to the signals it's sending.