Medically reviewed by Dr. Reina Punj, MBBS, PG Diploma in Endocrinology (University of South Wales), Lead Physician, Excelgenics Clinical Panel.
The most common side effects of magnesium glycinate are digestive: loose stools or diarrhoea, nausea and stomach cramps, usually when the dose is higher than the body handles comfortably. Serious problems are rare in healthy adults who stay within the recommended limit, but too much magnesium from supplements can be harmful, particularly for people with kidney disease. Magnesium bisglycinate side effects are the same, because magnesium glycinate and bisglycinate are two names for the same compound.
This guide covers what to expect, how much is too much, which medicines interact with magnesium and who should check with a doctor first. For a full overview of magnesium supplements, see our Magnesium Supplements Guide.
Common side effects of magnesium glycinate
According to the US National Institutes of Health Office of Dietary Supplements (NIH ODS), high doses of magnesium from supplements or medicines often cause diarrhoea, which can come with nausea and abdominal cramping.
The NIH notes that the forms most commonly linked with diarrhoea are magnesium carbonate, chloride, gluconate and oxide. Magnesium glycinate is not on that list, and many people find it gentle on the stomach, but that does not mean it can never cause digestive upset. Tolerance varies from person to person and depends mostly on the dose.
Typical, usually mild effects include:
- loose stools or diarrhoea;
- nausea;
- stomach cramps or discomfort.
These usually settle if you take the tablet with a light meal or stop the supplement. If they continue, stop taking it and speak to your doctor.
Magnesium bisglycinate side effects and the 350 mg upper limit
The NIH sets a Tolerable Upper Intake Level (UL) of 350 mg a day of magnesium from supplements and medicines for everyone aged 9 and over, including during pregnancy and breastfeeding. Lower limits apply to younger children (65 mg a day at 1–3 years and 110 mg a day at 4–8 years).
Three things are worth knowing about this limit:
- It counts elemental magnesium, not the weight of the whole compound. A label may list the magnesium bisglycinate weight first; the elemental magnesium figure is the one to check.
- It excludes food. Magnesium naturally present in food and drinks does not count, because healthy kidneys remove any excess in urine.
- It includes everything from supplements and medicines, such as multivitamins, magnesium-containing antacids and laxatives.
For example, Magneva Magnesium Bisglycinate 350mg + Vitamin B6 provides 350 mg of elemental magnesium per tablet, at one tablet a day. That is the full NIH upper limit on its own, so do not take other magnesium supplements, or magnesium-containing antacids or laxatives, alongside it unless your doctor advises it.
Signs of too much magnesium
Magnesium toxicity (hypermagnesaemia) is uncommon. The NIH notes that it has mostly been linked with very large doses of magnesium-containing laxatives and antacids, typically more than 5,000 mg a day, and that the risk rises with reduced kidney function or kidney failure. A few fatal cases have been reported.
Signs of magnesium toxicity can progress from:
- low blood pressure, nausea and vomiting, to
- muscle weakness, difficulty breathing and an irregular heartbeat, and, in severe cases, cardiac arrest.
These symptoms need urgent medical attention. They are not expected at label doses in healthy adults, but they are the reason the upper limit exists and the reason people with kidney problems need medical advice before taking magnesium.
Kidney disease
The kidneys are the main way the body gets rid of extra magnesium. If they are not working well, magnesium can build up in the blood. If you have chronic kidney disease, are on dialysis or have been told your kidney function is reduced, do not take a magnesium supplement unless your doctor has recommended it and is monitoring you.
Drug interactions
The NIH ODS lists the following interactions between magnesium and common medicines:
| Medicine | What happens | What to do |
|---|---|---|
| Bisphosphonates for bone health (e.g. alendronate) | Magnesium can reduce their absorption. | Take magnesium at least 2 hours before or after the bisphosphonate. |
| Tetracycline antibiotics (e.g. doxycycline) and quinolone antibiotics (e.g. ciprofloxacin, levofloxacin) | Magnesium can bind these antibiotics and reduce their absorption. | Take the antibiotic at least 2 hours before or 4–6 hours after magnesium. |
| Loop and thiazide diuretics (e.g. furosemide, bumetanide) | Long-term use can increase magnesium loss in urine. | Ask your doctor whether your magnesium should be checked. |
| Potassium-sparing diuretics (e.g. amiloride, spironolactone) | These reduce magnesium loss, so levels can rise. | Ask your doctor before adding a magnesium supplement. |
| Proton pump inhibitors (PPIs), acid-reducing medicines used for reflux or ulcers, taken for more than a year | Can lower blood magnesium; in some cases supplements alone did not correct it. | Your doctor may check your magnesium level; do not stop a prescribed medicine on your own. |
If you take any regular medicine, ask your pharmacist about timing. You can read more in Magnesium Deficiency Caused by Your Medications.
Pregnancy and breastfeeding
Magnesium needs are slightly different in pregnancy and breastfeeding, and the 350 mg supplemental upper limit still applies. Take a magnesium supplement during pregnancy or while breastfeeding only if your doctor or midwife advises it, and tell them about any prenatal vitamins you already take, as these may contain magnesium.
Who should ask a doctor first
- People with kidney disease or reduced kidney function
- Anyone who is pregnant or breastfeeding
- People taking bisphosphonates, tetracycline or quinolone antibiotics, diuretics or long-term PPIs
- People with any other ongoing medical condition
- Anyone already taking a multivitamin, antacid or laxative that contains magnesium
- Children: lower limits apply, so give magnesium supplements only on medical advice
If you think you may be low in magnesium, see our article on signs of magnesium deficiency and speak to your doctor, who can advise whether a test is needed.
Practical tips to reduce side effects
- Stick to the label dose. Do not take extra tablets to "catch up".
- Take it with water or a light meal if it upsets your stomach.
- Count every source. Check multivitamins, antacids and laxatives for added magnesium.
- Space it from medicines as shown in the table above.
- Stop and seek advice if you have persistent diarrhoea, vomiting, unusual weakness or an irregular heartbeat.
Frequently asked questions
Does magnesium glycinate have side effects?
It can. The most common are loose stools, nausea and stomach cramps, usually at higher doses. Many people take it without problems at the label dose, but no supplement is free of side effects for everyone.
Can I take magnesium glycinate every day?
Yes, it is designed for daily use at the dose on the label, as long as your total magnesium from supplements and medicines stays within 350 mg a day and you do not have kidney disease or other reasons to check with a doctor first.
Are magnesium bisglycinate tablet side effects different from capsules or powders?
The side effects come from the magnesium, not the format. What matters most is the elemental magnesium dose per day.
What happens if I take too much magnesium glycinate?
The first sign is usually diarrhoea. Much larger amounts, especially with poor kidney function, can cause low blood pressure, muscle weakness and an irregular heartbeat. Seek medical help if you have taken far more than the label dose or feel unwell.
References
- National Institutes of Health, Office of Dietary Supplements. Magnesium: Fact Sheet for Health Professionals. ods.od.nih.gov
- National Institutes of Health, Office of Dietary Supplements. Magnesium: Fact Sheet for Consumers. ods.od.nih.gov
This article is for general education and is not medical advice. Food supplements are not intended to diagnose, treat, cure or prevent any disease. Consult a qualified healthcare professional before starting any supplement, particularly if you are pregnant, breastfeeding, have a medical condition or take medication.
