Is 500mg of Magnesium Too Much? What You Need to Know

Yes, 500mg of magnesium is above the daily amount that an adult can take from supplements without increasing the risk of side effects. The NHS states that taking 400mg or less of magnesium from supplements each day is unlikely to cause harm. Higher amounts can cause side effects, particularly diarrhoea.

The Quick Verdict

If 500mg refers to the amount of elemental magnesium in a supplement, then it is a high dose and above the NHS amount of 400mg of magnesium per day from supplements that is unlikely to cause harm.

If 500mg refers to the amount of magnesium glycinate, citrate or another magnesium compound, then you need to look at how much ‘elemental magnesium’ it provides.

When taking a magnesium supplement, the other important consideration is who is taking it. Someone with reduced kidney function or another medical condition may not have the same risk profile as a healthy adult. Regular medicines and other magnesium-containing products also need to be considered.

My advice is simple: check the actual magnesium content rather than the marketing number on the front of the packet, and don’t assume that a high-dose supplement is appropriate simply because it is available to buy.

Medical Disclaimer

This article is for general educational purposes. It is not personalised medical advice and does not recommend a specific magnesium dose for you. If you have kidney disease, another medical condition, take regular medication, or are unsure whether a magnesium supplement is suitable for you, speak to your GP or pharmacist.

How Much Magnesium Do You Need Daily?

Magnesium is an essential mineral involved in a number of normal functions in the body.

The NHS states that adults aged 19 to 64 need around 300mg of magnesium a day for men and 270mg for women.

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NHS does not routinely recommend taking magnesium supplements and advices eating a healthy balanced diet. Good dietary sources include spinach, nuts and wholemeal bread. Most people should be able to obtain the magnesium they need from a varied and balanced diet.

It is important to remember that the amount of magnesium you need each day is not the same as the amount you need to take as a supplement. The NHS states that 400mg or less of magnesium per day from supplements is unlikely to cause harm.

Check the amount of elemental magnesium

If a product states 500mg on the label, it may not mean 500mg of elemental magnesium. This is where magnesium supplements can become confusing. Magnesium is available in several forms, including:

• magnesium glycinate
• magnesium citrate
• magnesium oxide
• magnesium chloride
• magnesium malate

These are magnesium compounds. The weight of the compound is not same as the amount of elemental magnesium it provides. For example, a label could say:

Magnesium glycinate – 500mg

and separately state:

Providing magnesium – 70mg

In that example, the product contains 500mg of the magnesium compound but provides 70mg of actual magnesium.

What Happens If You Take Too Much Magnesium?

The most common problem with taking a high amount of magnesium from supplements is diarrhoea. The NHS specifically states that taking high doses of magnesium, particularly more than 400mg, can cause diarrhoea. Large amounts can also cause:

• nausea
• vomiting
• stomach cramps
• stomach upset

UKHSA guidance similarly notes that ingesting large amounts of magnesium can cause nausea, vomiting, diarrhoea and stomach upset.

This does not mean that diarrhoea after taking magnesium automatically indicates serious toxicity. Magnesium salts can have a laxative effect, particularly at higher doses.

If symptoms begin after increasing your magnesium supplement, the dose is worth reviewing rather than simply assuming that a different supplement is needed.

Can Too Much Magnesium Be Dangerous?

It can be, particularly when very large amounts are involved.

UKHSA notes that people with kidney disease may be more sensitive to large amounts of magnesium because their kidneys may not be able to remove it from the body effectively.

This is one of the most important safety points when considering high-dose magnesium.

Severe magnesium excess can cause more serious effects, including low blood pressure, weakness, breathing problems and abnormal heart rhythm. These are not the expected effects of taking a standard magnesium supplement at a normal dose, but they are recognised features of significant magnesium excess.

NHS Specialist Pharmacy Service guidance also highlights the need for caution with magnesium treatment in renal impairment because of the risk of hypermagnesaemia, particularly in severe kidney disease, acute kidney injury and people receiving dialysis.

Who Needs to Be More Careful With Magnesium?

A magnesium supplement that is tolerated by a healthy adult may not be suitable for someone with an underlying medical condition. Particular caution is needed in people with reduced kidney function, especially those with more severe kidney disease, because the kidneys play an important role in removing excess magnesium from the body.

Anyone with an underlying medical condition, anyone taking regular prescribed medicines, or anyone using several supplements at the same time should speak to a GP or pharmacist if they are unsure whether a magnesium supplement is appropriate.

Can Magnesium Interact With Medicines?

Yes, magnesium can affect the absorption of some medicines when they are taken at the same time. This is particularly relevant with certain medicines where reduced absorption could affect their effectiveness.

Magnesium is also present in some medicines, including certain antacids and laxatives.

If you take regular medication, it is therefore worth checking the individual medicine rather than assuming magnesium can always be taken alongside it.

The correct timing between magnesium and another medicine depends on the medicine involved. A pharmacist can check this for you.

Can You Get Too Much Magnesium From Food?

The NHS recommends obtaining magnesium through a varied and balanced diet, with foods such as nuts, spinach and wholemeal bread providing dietary magnesium.

If you are eating a normal varied diet, there is no reason to assume that you need to restrict magnesium-rich foods simply because you are concerned about the dose of a supplement.

The concern discussed in this article is primarily high-dose supplemental magnesium.

What Should You Check Before Taking a Magnesium Supplement?

Before deciding whether a product contains too much magnesium, I would check these things:

• The elemental magnesium amount. Do not confuse the weight of magnesium glycinate, citrate or another compound with the actual magnesium provided.
• Your total supplemental intake. Check whether another vitamin tablet you are taking also contains magnesium.
• Your medicines as some medicines can interact with magnesium.
• Your kidney function and medical conditions. Reduced kidney function is particularly important when considering larger amounts.
• Why you are taking it. A higher dose is not automatically better, and UK Government guidance advises against high-dose supplements unless advised by a GP or healthcare specialist.

References

1. NHS – Vitamins and minerals: Magnesium
Information on daily magnesium requirements, dietary sources and NHS guidance on magnesium supplements.

2. GOV.UK – Food supplements guidance
UK Government guidance on the safe use of food supplements, including considerations for people with medical conditions or taking prescribed medicines.

3. UK Health Security Agency – Magnesium: General Information
Information on magnesium exposure, symptoms associated with excessive intake and increased sensitivity in people with impaired kidney function.

4. NHS Specialist Pharmacy Service – Treating acute hypomagnesaemia in adults
Professional UK guidance covering magnesium treatment, adverse effects and considerations in renal impairment.

Medical Review

Clinically reviewed by Sohaib Ahmed (MPharm)
GPhC-Registered Clinical Pharmacist & Independent Prescriber

iVitamin articles are written for general educational purposes and are not a substitute for individual medical advice.

If you are pregnant, breastfeeding, have kidney or liver disease, have another medical condition, or take prescription medication, speak to your GP or pharmacist before starting a new supplement.

iVitamin does not provide personalised medical advice, diagnosis, treatment or prescribing through this article.

Last reviewed: September 2026