Magnesium

Is magnesium safe?

For people with healthy kidneys, magnesium is one of the safest supplements you can buy. The body controls blood magnesium tightly and sends excess out in urine. Take too much and the first thing that happens is diarrhoea, which is why magnesium salts are also used as laxatives. That built-in warning sign is the main reason for its high score.

The two cases where caution matters are kidney disease and timing alongside some prescription drugs.

Two upper limits, one reason

The US National Academies set the upper limit for supplemental magnesium at 350 mg a day for adults and children over 8. EFSA's limit, which dates from 2001 and is still in force, is lower at 250 mg a day from age 4. Both are based on the same thing: the dose at which a meaningful share of people get loose stools. Neither is about organ damage.

Both limits apply to magnesium from supplements, medicines and fortified foods, not to magnesium in food. Nuts, seeds, whole grains and leafy greens supply most people with 250 to 350 mg a day without any risk.

Note the unit on the label. "Magnesium citrate 1,000 mg" may contain only about 150 mg of actual (elemental) magnesium. The limit refers to elemental magnesium.

When magnesium becomes dangerous

High blood magnesium, called hypermagnesaemia, causes nausea, flushing, low blood pressure, muscle weakness and slow breathing. In severe cases it stops the heart. Normal blood levels are about 1.7 to 2.3 mg/dL; severe toxicity is generally above 12 mg/dL.

Getting there with ordinary supplements is very hard with working kidneys. Published serious and fatal cases nearly always involve one of these:

• Kidney failure, where magnesium cannot be cleared.
• Large doses of magnesium-containing laxatives or antacids, often several grams a day, particularly in older people with constipation or bowel problems.
• Epsom salt (magnesium sulphate) taken by mouth in large amounts, or magnesium enemas.
• Children given adult laxative doses.

The NIH Office of Dietary Supplements notes that toxicity cases usually involve intakes above 5,000 mg a day from laxatives and antacids. We score organ toxicity at 88 because these cases are real but sit far outside normal supplement use.

Interactions that matter

Most magnesium interactions happen in the gut, where it binds to other drugs and stops them being absorbed:

Medicine	What happens	What to do
Tetracycline and quinolone antibiotics (doxycycline, ciprofloxacin)	Less antibiotic absorbed	Separate by at least 2 hours before or 4 to 6 hours after
Bisphosphonates (alendronate)	Less drug absorbed	Separate by at least 2 hours
Levothyroxine	Less thyroid hormone absorbed	Separate by at least 4 hours (label)
Potassium-sparing diuretics (amiloride, spironolactone)	Magnesium can build up	Ask your doctor
Loop and thiazide diuretics, long-term PPIs	Magnesium levels fall	Your doctor may test levels

The FDA warned in March 2011 that taking proton pump inhibitors such as omeprazole for long periods, in most cases more than a year, can cause low magnesium. In about a quarter of the cases it reviewed, supplements alone did not fix the level and the PPI had to be stopped. If you take a PPI long term and feel muscle cramps or palpitations, ask about a blood test rather than self-treating.

Is magnesium glycinate better?

Magnesium glycinate, also sold as bisglycinate, is magnesium bound to the amino acid glycine and is marketed above all for sleep and stress. Its real advantage is comfort: it draws less water into the gut than oxide or citrate, so it causes diarrhoea less often at the same dose. The absorption evidence is thin. In a 1994 crossover trial in 12 patients with part of the small intestine removed, 100 mg of magnesium was absorbed equally from glycinate and oxide overall (23.5% vs 22.8%), and better from glycinate only in the four patients who absorbed oxide worst. For sleep, a 2025 German trial in 155 adults found 250 mg of magnesium a day as bisglycinate improved an insomnia score slightly more than placebo after four weeks, a small effect.

Read the label carefully. Glycinate is only about 14% magnesium by weight, so "magnesium glycinate 1,000 mg" on the front gives about 140 mg of magnesium. On a US Supplement Facts panel, the number next to "Magnesium (as magnesium glycinate)" is the magnesium itself, and that is the figure that counts toward the 350 mg limit.

Product quality

Magnesium is a simple mineral salt, cheap to make, and independent testers rarely report contamination or major dose errors. Gummies are the exception worth knowing about: in May 2026 a US seller recalled its Adndale Magnesium Glycinate Gummies (400 mg) because they contained undeclared melatonin, a Class II recall in the FDA's enforcement database. That matters for anyone who drives early or takes other sedating medicines. The more common issue is marketing: claims that one form (glycinate, threonate, malate) is far better absorbed or works better for sleep or anxiety rest on small studies. If you want a third-party check, the USP VerifiedThird-party testingTesting of a supplement by an independent lab to check that it contains what the label says and is free of set contaminants.More in the glossary and NSF marks cover dose and contaminants.

Who should be careful

• People with chronic kidney disease, at any stage. Talk to your doctor before taking any magnesium, including antacids.
• People with heart block or myasthenia gravis, in whom magnesium can worsen symptoms.
• Anyone taking the medicines in the table above.
• Pregnant women: magnesium is commonly in prenatal vitamins and is safe at those doses, but ask before adding more.

Combining magnesium with vitamin D or creatine is common and causes no known problems.

How we scored it

Magnesium scores well on regulatory record (92), organ toxicity (88), dose safety (86) and quality (84). Interactions (80) are its weakest factor, though most are solved by spacing doses. The overall score puts it close to creatine and above melatonin, which people often take for the same reason: sleep.