Magnesium side effects: is it dangerous to take supplements?
Is it dangerous to take magnesium supplements?
For healthy people with normal kidney function, magnesium supplements at recommended doses are safe. The kidneys excrete any excess through the urine. Problems mainly arise when the dose is high or when the kidneys cannot regulate levels as they should.
Common side effects of magnesium
Most side effects concern the stomach and come from too high a dose or the wrong form.
- Loose stools and diarrhoea – most common, especially with oxide and citrate at high doses.
- Bloating and stomach cramps – when the gut draws in water.
- Nausea – usually if you take the supplement on an empty stomach.
If you switch form or lower the dose, the problems usually disappear. Glycinate is often gentler on the stomach than oxide – see the differences in our guide to magnesium forms.
How much magnesium is too much?
EFSA's upper limit for magnesium from supplements is 250 mg per day, on top of what you get from food. The limit is set precisely to avoid loose stools, not because lower doses would be acutely dangerous. Magnesium from food is not counted, since it is absorbed more slowly.
| Dose from supplements | What usually happens |
|---|---|
| Up to 250 mg/day | Safe for most people, rarely any trouble |
| 300–400 mg/day | Increased risk of loose stools |
| Very high doses | Should only be taken under medical supervision |
VitaNord Magnesium uses a well-absorbed form and is dosed within safe levels – gentle on the stomach.
See current price »Is magnesium dangerous for the heart?
For healthy people, recommended doses are not dangerous for the heart – on the contrary, magnesium is needed for normal heart muscle function. The risk applies to those with kidney failure or those taking certain heart and blood pressure medicines, where excessive magnesium levels can affect the rhythm. If you have a heart condition, take supplements only after consulting your doctor.
Who should be careful?
- Impaired kidney function – the kidneys cannot get rid of the excess.
- Certain medicines – magnesium can affect the absorption of antibiotics and thyroid medication, among others. Take them a few hours apart.
- Pregnant women and children – follow adjusted doses, see magnesium during pregnancy and for children.
If you are unsure about interactions, ask your pharmacist or doctor before you start.
How to reduce the risk of side effects
- Start with a lower dose and increase gradually.
- Take magnesium with food.
- Split the dose across the day instead of taking it all at once.
- Choose a well-absorbed form if oxide gives you loose stools.
If you need to find a gentle product, compare options in our guide to the best magnesium.
Which form causes the fewest side effects?
Stomach tolerance differs clearly between the forms. Oxide and citrate draw more water into the gut and more often cause loose stools at high doses, while glycinate and malate are usually better tolerated. If one form gives you trouble, switching is often the solution rather than stopping altogether.
| Form | Risk of loose stools |
|---|---|
| Oxide | High |
| Citrate | Moderate at high doses |
| Glycinate | Low |
| Malate | Low |
Signs of excessive magnesium levels
Truly high blood levels, known as hypermagnesaemia, are rare in healthy people with normal kidney function, since the kidneys excrete the excess. With impaired kidney function, however, it can occur. Signs to watch for:
- Nausea and vomiting.
- Muscle weakness and lethargy.
- Low blood pressure.
- Irregular heart rhythm in severe cases.
If you get such symptoms in connection with high doses, stop taking the supplement and contact a doctor. For healthy people on the recommended dose, this is nothing to worry about.
Magnesium and medicines – common interactions
Magnesium can affect how well certain medicines are absorbed. It is rarely a matter of danger, more often that the medicine's effect is reduced if you take them at the same time.
- Certain antibiotics (tetracyclines, quinolones) – take at least 2–3 hours apart.
- Thyroid medication (levothyroxine) – separate in time.
- Osteoporosis medicines (bisphosphonates) – take on an empty stomach, apart from magnesium.
- Diuretics – can affect magnesium levels in either direction.
If you take medication regularly, ask your doctor or pharmacist before you start. It is a simple check that avoids unnecessary problems.
Is magnesium safe to take long term?
Yes, for healthy people, long-term use at the recommended dose is safe. Magnesium is a nutrient the body needs throughout life, and it does not build up to harmful levels as long as the kidneys work and you stay under 250 mg from supplements per day. You do not need to take breaks or "rest" from magnesium the way you might with certain other preparations. If you want to stop, you can do so abruptly without tapering.
Side effects in children and pregnant women
Both pregnant women and children may need magnesium, but the doses are lower and should be adjusted. For children, age determines how much is appropriate, and supplements should not be given without reason. Pregnant women have an increased requirement but should follow medical advice on levels. Read more in our dedicated guide to magnesium during pregnancy and for children before giving supplements to these groups.
What to do if you get side effects
- Halve the dose and see if the trouble disappears.
- Take the magnesium with food instead of on an empty stomach.
- Switch from oxide or citrate to a gentler form such as glycinate.
- Split the dose across the day.
If the problems persist despite this, or you get symptoms of excessive levels, stop taking the supplement and contact a doctor.
Frequently asked questions
Can magnesium cause diarrhoea?
Yes, loose stools are the most common side effect. Magnesium draws water into the gut, which can cause diarrhoea at high doses – especially with oxide and citrate. Lower the dose, take the supplement with food or switch to a gentler form such as glycinate. If you stay within 250 mg per day, the risk is small for most people.
Is it dangerous to take magnesium every day?
No, for healthy people with normal kidney function, daily magnesium at recommended doses is safe. The body gets rid of any excess. Stay within 250 mg from supplements per day. If you have kidney problems or take medicines affected by magnesium, check with your doctor before taking it regularly.
Can you overdose on magnesium?
From food, it is practically impossible, since the kidneys regulate the levels. From supplements, very high doses are required for a genuine overdose, and the risk mainly concerns people with impaired kidney function. Signs of excessive levels include nausea, low blood pressure and muscle weakness. Stick to the recommended dose and you will avoid it.
Does magnesium affect other medicines?
Yes, magnesium can reduce the absorption of certain antibiotics, thyroid medication and osteoporosis medicines. Take them a few hours apart from the magnesium. Some diuretics and heart medicines also affect magnesium levels. If you take medication regularly, ask your doctor or pharmacist before starting supplements.