Magnesium 101

Is Too Much Magnesium Bad For You?

Here at AboutMagnesium, we often talk about how common magnesium deficiency is and how it can negatively affect your health. But can you have too much of a good thing? Is too much magnesium bad for you? The short answer is yes, but read on to find out why this is unlikely and how to make sure it doesn’t happen to you! 

What is magnesium? 

Magnesium is a mineral that you need to maintain optimal physical and mental health. It’s involved in hundreds of biochemical processes, playing a key role in everything from immune system regulation right down to DNA synthesis. As an electrolyte, it also helps to control the electrical system that powers your heart, muscles, and nerves. 

In a nutshell, it’s a pretty important mineral! And when we don’t get enough, we’re at risk of serious conditions like cardiovascular disease, high blood pressure, type 2 diabetes, osteoporosis, ADHD, and Alzheimer’s disease.

How much magnesium do I need?

Magnesium is an essential mineral, which means your body can’t produce it by itself. Instead, you need to get it from your diet by eating magnesium-rich foods like leafy green vegetables, seeds and nuts, lentils, whole grains, and fatty fish.  

The recommended magnesium dosage and intake vary depending on your age and sex. The table below shows the adequate intake (AI) and recommended dietary allowance (RDA) from the National Institute of Health.

Birth to 6 months30 mg*30 mg*
7–12 months75 mg*75 mg*
1–3 years80 mg80 mg
4–8 years130 mg130 mg
9–13 years240 mg240 mg
14–18 years410 mg360 mg
19–30 years400 mg310 mg
31–50 years420 mg320 mg
51+ years420 mg320 mg

Can I get too much magnesium?

Even if you eat a magnesium-rich diet, it’s very unlikely that you’d find yourself consuming too much magnesium. In fact, we know that most people have the opposite problem: they don’t get nearly enough. This can happen for one or more reasons, including: 

  • Low intake of foods with magnesium. 
  • Depletion of magnesium content in food due to excessive processing or poor farming practices. 
  • Certain health conditions increase your magnesium needs or affect how well it’s absorbed by your body, e.g. stress, alcohol abuse, gastrointestinal disorders, kidney problems, type 2 diabetes, and pregnancy. 

But what if you’re taking a magnesium supplement too? Well, the 375-400mg limit refers to supplements only. So even if you’re packing magnesium-rich foods into your diet all day long, you can still take a magnesium supplement if you feel that you need it. Simply make sure to take no more than 375-400mg every day. 

What if I take too much magnesium? 

If you do exceed the recommended intake, rest assured that you’re very unlikely to experience serious problems or overdose on magnesium (there is a catch, though, so keep reading!). The “toxic level” of magnesium is actually incredibly high, with poisoning occurring at doses of around 5,000mg a day. If you were taking a supplement that contained 350mg of magnesium, then, you’d have to take at least 14 times your normal dose to start experiencing toxic effects! 

But what about if you wanted to exceed the daily dosage by just a little? For example, some studies have shown that 500mg or 600mg a day is effective for relief from migraines, while 450mg (and sometimes more) seems to be an optimal dose for mood management. Technically, that’s “too much” magnesium, but is it harmful? 

For most people, no. The 400mg upper limit on magnesium supplements is simply the point at which side effects become more likely (but not guaranteed). When taking more than 400mg, some people start to experience mild digestive side effects like nausea, bloating, or diarrhea. 

The more you take, the greater the likelihood. However, you can reduce the risk of side effects by choosing the best type of magnesium that’s better tolerated by the stomach, such as taurate, glycinate, or malate

The catch!

Even though a little “too much” magnesium is fine for most people, we did mention that there’s a catch. Too much magnesium is unlikely to be harmful to a healthy person, but there are certain circumstances where too much magnesium can in fact be bad for you. Let’s take a look at who needs to be extra careful and why… 

People with kidney disease or kidney failure 

One reason you’re unlikely to take too much magnesium is that your kidneys are very efficient at getting rid of any excess. If you have more than you need in your body, your kidneys will simply flush it out in your urine. However, if you have kidney disease or kidney failure, this may not happen, allowing the magnesium to build up to dangerous levels (known as hypermagnesemia). 

Pregnant women with pre-eclampsia 

Pre-eclampsia is a condition that causes dangerously high blood pressure in pregnant women. Treatment involves very high doses of magnesium, so you’ll need to be monitored very closely to prevent hypermagnesemia. In this case, you should not take any magnesium supplements until your medical team tells you it’s safe to do so.  

People taking medications 

Magnesium interacts with lots of medications you might be taking for health conditions. What is considered “too much” magnesium for you might therefore be a bit lower than the standard recommendations. Here’s why… 

Magnesium may cause you to absorb too much medication, increasing the effects (and side effects). Also, the medication may not be out of your system by the time you take your next dose. Some diabetes medications interact with magnesium in this way, potentially lowering blood sugar by too much. 

Magnesium can have the opposite effect, too, causing you to absorb too little medication and reducing its effectiveness. Additionally, the medication may wear off before you take your next dose. Medications that commonly interact with magnesium in this way include: 

  • Bisphosphonates (for osteoporosis)
  • Anticonvulsants (for seizures)
  • Thyroid medications
  • Many antibiotics

Finally, magnesium shares the same effects as some medications, amplifying their effect when taken together. Common examples include: 

  • Calcium channel blockers for managing high blood pressure
  • Muscle relaxants
  • Anticoagulant or antiplatelet medications to slow blood clotting

These are just a few examples, so be sure to check with your doctor or pharmacist if you’re taking any medications. They can advise you on how much magnesium is “too much”, how much you should take, and how to take it safely. 

People with health conditions 

People with certain health conditions, such as heart disease, some gastrointestinal conditions, and thyroid disease, might be more vulnerable to magnesium toxicity. This can happen whether or not you take medications for your conditions, so check with your doctor to find out how much is too much magnesium for you.    

How do I know how much magnesium I’m taking? 

You should see the magnesium content listed on the label of your supplement. However, keep in mind that your supplement will be a combination of magnesium and something else, such as malic acid (magnesium malate). You’re only looking for the amount of magnesium, also known as the elemental magnesium content. So 320mg of magnesium might be written as: 

“320mg of magnesium from 1600 mg of magnesium malate.” 

“320mg elemental magnesium from magnesium malate.”

“1600mg of magnesium malate with 320mg magnesium.”

This dosage might be spread across multiple servings, e.g. two capsules once a day, or one capsule three times a day. Be sure to read the label carefully to avoid taking too much! 

What if I’ve taken too much magnesium?

The following signs might mean that you’ve taken too much magnesium: 

  • Diarrhoea
  • Nausea or vomiting 
  • Muscle weakness
  • Lethargy
  • Facial flushing 
  • Urine retention
  • Confusion or disorientation
  • Dizziness
  • An irregular heartbeat 

Mild digestive side effects tend to resolve quickly after you stop taking magnesium or lower your dose. However, if you’re experiencing more serious effects, it’s important to seek medical advice quickly as a true magnesium overdose can be very dangerous.

The bottom line

To summarise, taking a little too much magnesium is unlikely to be bad for you. However, “too much” can mean different things to different people. It’s best to stick to the recommended amount and, if you have health problems or take medications, speak to your doctor to make sure you’re taking magnesium safely.