Too much magnesium: reading the 250 mg limit
Futures Nutrition Editorial Team · 10 August 2026
Too much magnesium: reading the 250 mg limit
10 August 2026
The short answer first: with normal kidney function, magnesium from food is practically impossible to overdo – surplus magnesium is excreted by the kidneys. What is reached first is not a toxicity threshold but a tolerance threshold in the gut. That is exactly where the figure quoted everywhere comes from: 250 mg of magnesium per day from food supplements. Anyone above that risks not primarily poisoning but soft stools up to diarrhoea – unpleasant, but over again within one or two days.
The question becomes serious in a different case: with impaired kidney function. Then it is no longer about tolerance but about the amount itself – and about medical advice rather than self-experiment.
Magnesium contributes to normal muscle function.
The 250 mg count something different from the 375 mg
The most common error of reasoning on the subject of overdosing is a comparison that does not work in the first place. The pack says 375 mg as the nutrient reference value (NRV), every guide says 250 mg as the maximum level – and from that people conclude that somebody must be wrong.
Both figures are correct. They simply do not count the same things.
| Figure | Meaning | Counts in | Does not count in |
|---|---|---|---|
| 375 mg | nutrient reference value (NRV), the basis for the percentage on the label | everything, regardless of the source | – |
| 350 / 300 mg | estimated values for an adequate intake (men / women from 25 years) | the entire daily intake | – |
| 250 mg | recommended daily maximum level for food supplements | food supplements, fortified foods, dissolved magnesium salts in water | magnesium naturally present in foods |
So the 250 mg are not a cap for the whole day, only for what comes on top of the normal diet. A plate of wholemeal pasta with spinach and a handful of pumpkin seeds do not fall under it. Which figure applies to which situation in life is set out in detail in Magnesium daily requirement: 375, 350 or 250 mg?.
Where the 250 mg come from
The figure is older than most labels would suggest. The EU's Scientific Committee on Food (SCF) derived a tolerable upper intake level (UL) of 250 mg of additional magnesium per day in 2001. The determining effect was expressly osmotically induced diarrhoea – nothing else. Up to 250 mg per day no such effect was observed in the studies evaluated; mild diarrhoea occurred in a small proportion of adults from around 360 to 365 mg of additional magnesium.
The German Federal Institute for Risk Assessment (BfR) reviewed this value in 2017 against newer human studies and confirmed it: 250 mg per day from food supplements, spread over at least two portions. There is a plain reason for the splitting – in the studies the value comes from, the amount was likewise given over two or more portions, and that improves tolerance. The BfR also points to indications that the effect can occur in a small proportion of adults from around 300 mg.
Important for placing the figure: it applies to people from four years of age, including pregnant and breastfeeding women. For children under four no maximum level can be given for lack of data – which does not mean "harmless" but "not assessable".
What "too much" concretely means in everyday life
Magnesium that the gut does not absorb stays there. It binds water – the stool becomes softer, in larger amounts liquid. It is the same physical mechanism for which magnesium salts are used in medicine as osmotic laxatives, though there in amounts many times higher.
Three things follow from this:
- The single portion counts for more than the daily total. The percentage that is absorbed falls as the single amount rises – the rest stays in the gut. 2 × 125 mg are therefore regularly better tolerated than 250 mg at once. Which moment lends itself to that and what gaps to medicines are needed is in Taking magnesium: morning, evening or split?.
- The compound makes a difference – but not to the effect. Forms differ in solubility and tolerance, not in the authorised claims. Anyone with complaints at the same number of milligrams can try a different compound; the differences are described in Magnesium forms compared: bisglycinate, citrate & co..
- It is not a cleansing or detox signal. Soft stools after a large portion of magnesium do not mean that "the body is flushing something out" or that it "has had enough". They only mean that the single amount was too large.
The effect is completely reversible. In the underlying investigations it disappeared after one to two days as soon as the amount was reduced.
If it has happened
The sequence in everyday life is unspectacular: halve the single portion, spread it over two occasions, take it with a meal rather than on an empty stomach, drink enough. A forgotten portion is not made up double the next day – that produces exactly the large single amount that causes the problem.
If complaints persist or occur at ordinary amounts, the question belongs in a doctor's surgery. Persistent diarrhoea has many possible causes; that the magnesium of all things is to blame is a supposition, not a diagnosis.
When it is about more than tolerance
The kidneys regulate magnesium balance: what is too much is excreted. That is why an actually elevated magnesium level in the blood (hypermagnesaemia) is rare in healthy adults – as a rule it arises when that excretion no longer works.
Caution is therefore appropriate in these situations, regardless of how well a product is tolerated:
- Impaired kidney function. Food supplements containing magnesium are not suitable here without medical advice. That also applies to amounts that are completely unremarkable for other people.
- Magnesium-containing medicines. Antacids for heartburn and magnesium-containing laxatives often contain a multiple of what is in a food supplement. Anyone taking both is adding up – and usually does not know it.
- Long-term medication. For several groups of medicines a minimum gap in time to magnesium applies, because absorption is otherwise impaired. That is an interaction, not a quantity problem – what is binding is the package leaflet.
For healthy adults with functioning kidneys it remains the case: the limit you realistically reach is that of the gut, not that of the metabolism.
Mineral water and fortified foods: the blurred edge
One detail of the EU value is readily overlooked: it refers to readily soluble magnesium compounds – from food supplements, from fortified foods and from water. Not meant is the magnesium that occurs naturally in foods.
Mineral water therefore sits exactly on the edge, and honestly the classification is not the same in every source. In practice it only becomes relevant with strongly mineralised waters anyway: under the German mineral and table water regulation a natural mineral water may only be advertised as "containing magnesium" from more than 50 mg of magnesium per litre. There are waters with 100 mg/l and more – at one and a half litres a day that is 150 mg, so more than half the recommended maximum level. Anyone drinking such a water and taking a product at the upper limit should add the two together. Which foods and drinks contribute how much is in Magnesium in food: table & realistic portions.
The same applies to combinations: a multi-preparation, a separate magnesium product and a fortified sports drink on the same day quickly add up to a total nobody planned.
What this means for shopping
The check takes twenty seconds and consists of two moves:
- Find the "magnesium" line in the nutrition table – not the figure on the front. What is declared there is elemental magnesium, independent of the compound.
- Look at what the figure refers to. "Per daily portion" can mean one, two or three tablets. Only that figure is comparable with the 250 mg.
Products whose daily portion is clearly above 250 mg of elemental magnesium are available in the shops – the BfR recommendation is not a legal maximum level but a recommendation. Knowing it is nevertheless a better basis than the assumption that more is automatically better.
Our magnesium bisglycinate 150 mg provides 150 mg of elemental magnesium per tablet, that is 40 % of the nutrient reference value. Two tablets a day come to 300 mg – split over two occasions, as the recommendation provides, but above the 250 mg for food supplements. Anyone wanting to go by that figure stays with one tablet.
With combination products such as hawthorn + magnesium the same calculation applies: what counts is the amount of magnesium per daily portion, not the number of ingredients. An overview of all products is in the category minerals.
Food supplements are not a substitute for a balanced and varied diet and a healthy lifestyle.
The authorised claims for magnesium
Permitted is exclusively this list (Regulation (EU) No 432/2012):
- Magnesium contributes to the reduction of tiredness and fatigue.
- Magnesium contributes to normal muscle function.
- Magnesium contributes to the normal functioning of the nervous system.
- Magnesium contributes to electrolyte balance.
- Magnesium contributes to normal energy-yielding metabolism.
- Magnesium contributes to the maintenance of normal bones and teeth.
These claims are not tied to any particular amount above the labelling threshold – and above all: a larger amount makes none of the statements stronger. More magnesium does not mean more effect, only a larger share that stays unused in the gut.
Frequently asked questions
Can I take in too much magnesium through food?
With normal kidney function that is not to be expected. The EU maximum level expressly does not refer to the magnesium that occurs naturally in foods. Surplus amounts are excreted by the kidneys.
Is diarrhoea after magnesium a sign that my body has had enough?
No. It shows that the single amount was too large – the share that was not absorbed binds water in the gut. It says nothing about the fill level of the magnesium stores. The usual answer to it is a smaller portion, not a different product.
I have been taking 400 mg a day for months. Is that dangerous?
That amount is above the recommendation for food supplements. With healthy kidneys the effect to be expected is gastrointestinal and reversible, not lasting. If you have complaints, take medicines permanently or do not know your kidney values, asking at the pharmacy or the doctor's surgery is the right route – there it can also be clarified whether the amount makes sense in your situation.
Does the maximum level also apply in pregnancy and breastfeeding?
The EU value of 250 mg of additional magnesium expressly includes pregnant and breastfeeding women. For children under four there is no derived maximum level, because the data basis is missing.
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Sources: Regulation (EU) No 432/2012 (authorised claims); Scientific Committee on Food, Opinion on the Tolerable Upper Intake Level of Magnesium, 2001; German Federal Institute for Risk Assessment, "BfR assesses daily maximum level for magnesium in food supplements", 2017; German mineral and table water regulation, annex to § 9.
