Magnesium glycinate vs citrate vs oxide: what the evidence says

Magnesium is an essential mineral involved in hundreds of enzyme reactions, including those behind muscle and nerve function, energy release and bone formation. Most people get it from food such as leafy greens, nuts, seeds, wholegrains, beans and maize meal. In South Africa, people often look into magnesium for cramps, sleep, stress, constipation or headaches, and pharmacy shelves now carry glycinate, citrate, oxide and slow-release products side by side. The labels don't make the choice easy.

What the evidence shows

This review only counts human studies. Grades mean: strong (consistent results from several good-quality trials or meta-analyses), moderate (good trials exist, but effects are small, trials are few or results vary), weak (small or low-quality studies, mixed results) and insufficient (too little human research to judge).

• Raising blood magnesium. Strong. Supplements reliably raise serum magnesium. A 2016 meta-analysis of 34 placebo-controlled trials found around 300 mg a day, or one month of use, was enough to see a rise.
• Blood pressure. Moderate. In the same meta-analysis (2,028 adults, median 368 mg a day for about three months), systolic pressure fell by an average of 2.0 mmHg and diastolic by 1.8 mmHg. A small effect.
• Constipation (magnesium oxide). Moderate. In a Japanese placebo-controlled trial, 1.5 g of magnesium oxide a day for 28 days improved overall symptoms in 68% of people, against 12% on placebo. That is a laxative dose, far above typical supplement amounts.
• Migraine frequency. Moderate. A 2012 US neurology guideline rated oral magnesium as "probably effective" at reducing how often migraines occur, based on a small number of trials.
• Sleep in older adults with insomnia. Weak. A 2021 meta-analysis found only three small trials (151 people). Time taken to fall asleep shortened modestly, but the authors rated the evidence low quality.
• Anxiety and stress. Weak. A 2017 systematic review found suggestive results in people with mild anxiety, but most studies were poorly designed.
• Night-time leg cramps in older adults. Weak. A Cochrane review concluded magnesium is unlikely to give a clinically meaningful reduction in ordinary leg cramps in older adults. Results in pregnancy conflict.
• One form beating another on a health outcome. Insufficient. There are no good head-to-head trials comparing glycinate, citrate and oxide on sleep, cramps, mood or blood pressure.

So does the form matter?

For absorption, somewhat. Magnesium citrate dissolves well, and a randomised, double-blind study found it produced higher blood magnesium than magnesium oxide or an amino-acid chelate, both after a single dose and after 60 days. Magnesium oxide packs the most magnesium into a small tablet, but less of it is absorbed and more stays in the gut, which is why it works as a laxative. Magnesium glycinate (usually sold as bisglycinate) binds magnesium to the amino acid glycine. It is widely described as gentler on the stomach and better for sleep. The first claim is plausible; the second hasn't been examined in quality trials.

The practical takeaway: absorption differences are real, but nobody has shown they change outcomes that matter. How much elemental magnesium you take, and whether your gut tolerates it, probably matter more than the form named on the box.

Doses used in studies

The amounts below are what researchers gave participants. They aren't recommendations.

The blood pressure meta-analysis above reported a median of 368 mg a day; a Cochrane review summarised by the NIH covered doses of roughly 243 to 973 mg a day. The constipation trial above used 1.5 g of magnesium oxide a day, which supplies roughly 900 mg of elemental magnesium. Migraine trials summarised by the NIH used up to 600 mg a day. Doses in the sleep and anxiety studies varied.

For context, the US National Institutes of Health (NIH) recommends 400 to 420 mg a day for adult men and 310 to 320 mg for adult women, including food, and sets an upper limit of 350 mg a day from supplements and medicines. The European Food Safety Authority (EFSA) sets a lower upper level of 250 mg a day for supplemental magnesium in adults, and the UK's NHS says 400 mg a day or less from supplements is unlikely to cause harm. Many study doses sit above these levels; the NIH notes that the doses typically used for migraine exceed the upper limit and should only be used under medical supervision.

Safety, side effects and interactions

The most common side effects are diarrhoea, nausea and stomach cramps. They're more likely with magnesium oxide and with higher doses.

Serious toxicity (hypermagnesaemia) is rare in healthy people because the kidneys clear excess magnesium. Risk rises sharply with kidney disease and with very large doses of magnesium-based laxatives or antacids. Signs include low blood pressure, nausea and vomiting, facial flushing, muscle weakness, drowsiness and an irregular heartbeat.

If someone has taken a large amount of a magnesium product, or has muscle weakness, confusion, fainting or an irregular heartbeat after taking one, call an ambulance on 10177, or 112 from a cell phone.

The main interactions described by the NIH are:

• Bisphosphonates (such as alendronate, for osteoporosis): magnesium can reduce absorption, so the NIH suggests taking them at least two hours apart.
• Tetracycline and quinolone antibiotics (such as doxycycline or ciprofloxacin): magnesium can bind to them. The usual advice is to take the antibiotic at least two hours before or four to six hours after magnesium.
• Diuretics: loop and thiazide diuretics (such as furosemide or hydrochlorothiazide) can increase magnesium loss, while potassium-sparing diuretics can reduce it.
• Proton pump inhibitors (such as omeprazole or pantoprazole): long-term use (typically more than a year) can lower magnesium levels.
• Some ARVs, such as dolutegravir (part of the TLD combination): the NIH advises people taking supplements, antacids or laxatives that contain magnesium to follow their prescriber's instructions on how to time them with dolutegravir.

Speak to your doctor, clinic or pharmacist first if you have kidney disease, a heart rhythm condition or myasthenia gravis, if you take any of the medicines above, or if you're pregnant or breastfeeding. Children's needs and safe limits are different from adults'.

South African regulatory status

In South Africa, magnesium supplements are regulated by the South African Health Products Regulatory Authority (SAHPRA) as complementary medicines, in the "health supplements" subcategory of Category D under the Medicines and Related Substances Act. SAHPRA sets rules on the substances that may be used, labelling, and the health claims that may be made.

Labels must carry the words "Complementary Medicine" and "Health Supplement", and any product that SAHPRA has not registered must carry this exact disclaimer:

This unregistered medicine has not been evaluated by the SAHPRA for its quality, safety or intended use.

Magnesium bisglycinate, citrate and oxide forms appear on SAHPRA's list of permitted health-supplement substances. A product claiming to treat or prevent a disease would need registration as a medicine. The framework continues to be updated, so details can change.

What to look for when buying

• Elemental magnesium per daily dose. The big number on the box may be the weight of the whole compound, so check the ingredients panel for elemental magnesium per dose.
• Combination products. Some local magnesium products also contain other vitamins or minerals. Check the full ingredient list, especially if you take other supplements.
• Slow-release or enteric-coated tablets. These are common in South Africa. They're designed to release magnesium gradually, but there's no strong evidence that this improves outcomes.
• The SAHPRA statement and category line. The unregistered-medicine disclaimer and the words "Complementary Medicine" and "Health Supplement" show the product is labelled under the current rules.
• Third-party testing. Imported brands may carry NSF Certified for Sport, Informed Sport or USP Verified marks. They indicate batch testing for label accuracy and, for the sport marks, banned substances. They don't mean a product works.
• Your total intake. Add up magnesium from multivitamins, cramp formulas, effervescent tablets and sleep blends.

FAQ

Which magnesium is best for cramps?

For ordinary night-time leg cramps in older adults, a Cochrane review found magnesium is unlikely to make a meaningful difference, whatever the form. Frequent or severe cramps are worth discussing with a doctor, as they can have other causes, including some medicines.

Do I need a prescription for magnesium in South Africa?

No. Magnesium health supplements are sold over the counter at pharmacies, health shops and supermarkets. Magnesium given in hospital, or prescribed for a diagnosed deficiency, is a different matter.

Is slow-release magnesium better than glycinate?

There's no good evidence either way. Slow-release tablets may suit people who get stomach upset, and so may glycinate. Compare elemental magnesium per dose and price.

Can I take magnesium with ARVs?

Timing matters. The NIH advises people on dolutegravir to follow their prescriber's instructions on how to time magnesium-containing supplements, antacids or laxatives. Ask your clinic or pharmacist before you start.

Why does my magnesium label say "unregistered medicine"?

The regulations require that disclaimer on any complementary medicine SAHPRA hasn't registered. It doesn't mean the product is illegal or unsafe; it means SAHPRA hasn't assessed it.

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