Taking magnesium supplements? Learn why people with kidney problems and those taking certain medications should be cautious, plus the safe limits and common side effects of magnesium.
Anyone Taking Magnesium Should Know About These 2 Important Warnings
Magnesium is an essential mineral involved in hundreds of processes throughout the body, including normal muscle and nerve function, blood-pressure regulation, blood-sugar control, and energy production.
For many healthy adults, getting magnesium from foods such as nuts, seeds, beans, whole grains, and leafy green vegetables is considered safe. But taking magnesium supplements or magnesium-containing medicines requires more care.
Two groups in particular should be cautious.
1. People With Kidney Disease or Reduced Kidney Function
Your kidneys normally remove excess magnesium from your body through urine.
When kidney function is significantly impaired, the body may have difficulty getting rid of extra magnesium. As a result, magnesium from supplements, antacids, or laxatives can build up to potentially dangerous levels.
The NIH notes that the risk of magnesium toxicity increases when kidney function is impaired or when kidney failure is present.
People with:
- Chronic kidney disease
- Reduced kidney function
- Kidney failure
- Those receiving dialysis
should therefore not start high-dose magnesium supplements on their own.
A healthcare professional can determine whether magnesium is appropriate and whether blood tests or a dose adjustment are needed.
2. People Taking Certain Medications
Magnesium supplements can interfere with the absorption or effectiveness of some medicines.
One important example is certain antibiotics, including tetracyclines and quinolone antibiotics. Magnesium can bind to these medicines in the digestive tract and reduce their absorption.
Magnesium can also interfere with the absorption of some oral bisphosphonates, medicines commonly used for osteoporosis.
The timing of doses can matter. Depending on the medication, healthcare professionals may recommend separating magnesium from the medicine by several hours.
Some medications can also change magnesium levels in the body. For example, certain diuretics can increase or decrease magnesium loss, while long-term use of some proton-pump inhibitors can contribute to low magnesium levels.
What Should You Do If You Take Prescription Medicine?
Don’t automatically stop your medication.
Instead, tell your doctor or pharmacist that you are taking—or are considering taking—a magnesium supplement. They can check whether there is an interaction and tell you how far apart to take the products.
How Much Supplemental Magnesium Is Too Much?
For adults, the NIH’s tolerable upper intake level for magnesium from dietary supplements and medications is 350 mg per day.
Importantly, this limit does not include magnesium naturally present in foods.
Taking more than this amount does not necessarily mean something dangerous will happen immediately, but higher supplemental doses increase the likelihood of side effects and should generally be used only with appropriate medical guidance.
Signs You May Be Taking Too Much
Excess magnesium from supplements can cause:
- Diarrhea
- Nausea
- Abdominal cramping
Extremely high levels can be much more serious and may cause low blood pressure, muscle weakness, difficulty breathing, abnormal heart rhythms, and potentially cardiac arrest.
Food Is Different From Supplements
There is an important distinction between magnesium obtained from food and concentrated magnesium supplements.
For healthy people, the body generally handles magnesium from food well because the kidneys remove excess amounts.
Magnesium supplements and magnesium-containing medications can provide much larger doses in a concentrated form, which is why extra caution is necessary.
Good dietary sources include:
- Pumpkin seeds
- Almonds and other nuts
- Beans and legumes
- Whole grains
- Spinach and other leafy greens
- Some dairy products
- Fortified foods
The Bottom Line
Magnesium is an important nutrient, but more isn’t always better.
If you have kidney disease or reduced kidney function, speak with a healthcare professional before taking supplemental magnesium. And if you take prescription medicines—particularly certain antibiotics, osteoporosis medicines, diuretics, or long-term acid-reducing medicines—ask a pharmacist or doctor about possible interactions.
For most people, a balanced diet is the safest foundation for meeting magnesium needs. Supplements can be useful when there is a genuine need, but they should be chosen and dosed carefully rather than taken simply because magnesium is marketed as a cure-all.