Magnesium Glycinate vs Citrate vs Oxide: Which Form Should You Take?

Walk into any pharmacy or browse iHerb and you will find a dozen types of magnesium: glycinate, citrate, oxide, threonate, taurate, malate, and more. They all contain elemental magnesium, but the compound it is bound to dramatically affects how well your body absorbs it, what side effects you might experience, and what it is best suited for.

Roughly 50% of Australians do not meet the recommended dietary intake for magnesium (320 mg/day for women, 420 mg/day for men). So supplementing makes sense for many people — but choosing the wrong form can mean poor absorption, stomach upset, or paying more than you need to.

This guide compares the five most common magnesium forms available in Australia, covering absorption, evidence, side effects, and cost per serve.

What it is: Magnesium bound to glycine, an amino acid that itself has calming and inhibitory neurotransmitter properties.

Absorption: High. Glycinate is one of the most bioavailable forms of magnesium because the amino acid chelate is well-absorbed in the small intestine. A 2019 study in Nutrients found that organic magnesium salts (including glycinate) had significantly higher bioavailability than inorganic forms.

Best for: Sleep, anxiety, stress, muscle relaxation. Glycine independently supports sleep — a 2012 study in Neuropharmacology showed it lowers core body temperature, a key trigger for sleep onset. Combined with magnesium's GABA-supporting effects, this form delivers a dual mechanism for relaxation.

Side effects: Well-tolerated. Much less likely to cause loose stools compared to citrate or oxide because glycine is absorbed efficiently, leaving less unabsorbed magnesium in the gut.

Typical dose: 200–400 mg elemental magnesium per day, taken 30–60 minutes before bed.

Price in Australia: $0.10–0.50 per serve depending on brand. Powder forms (like BulkSupplements) tend to be cheapest; capsules from brands like Life Extension or Thorne cost more but are more convenient.

What it is: Magnesium bound to citric acid. One of the most widely available and studied forms.

Absorption: High. Citrate has good bioavailability — a 2003 study in Magnesium Research comparing four magnesium preparations found citrate was absorbed significantly better than oxide. It is often considered the "gold standard" for general magnesium supplementation.

Best for: General magnesium deficiency, constipation relief, muscle cramps. Citrate has a mild osmotic laxative effect, which makes it genuinely therapeutic for constipation but potentially inconvenient for people with sensitive digestion.

Side effects: Can cause loose stools and diarrhoea, especially at higher doses. This is the main drawback compared to glycinate. Start with a lower dose and increase gradually.

Typical dose: 200–400 mg elemental magnesium per day, with or without food.

Price in Australia: $0.08–0.30 per serve. Generally cheaper than glycinate. Widely available at Chemist Warehouse, Priceline, and online.

What it is: Magnesium bound to oxygen. Contains the highest percentage of elemental magnesium by weight (~60%), so tablets can contain large amounts in a small pill.

Absorption: Low. Despite containing more elemental magnesium per pill, oxide has the lowest bioavailability of common forms — as low as 4% according to a 2001 study in Journal of the American College of Nutrition. Most of it passes through the digestive tract unabsorbed.

Best for: Constipation relief (specifically, it works because it is poorly absorbed — the unabsorbed magnesium draws water into the intestine). Not ideal for correcting deficiency or for sleep/anxiety support.

Side effects: Significant gastrointestinal effects — bloating, gas, diarrhoea. The most likely form to cause stomach upset.

Typical dose: Labels often say 400–500 mg, but the actual absorbed amount may be as low as 16–20 mg. You would need much larger doses to match the effective absorption of glycinate or citrate.

Price in Australia: $0.03–0.10 per serve. The cheapest option by far, which is why it is so common in pharmacy brands. But on a per-absorbed-milligram basis, it may not be cheaper at all.

Bottom line: Unless you specifically want a laxative effect, oxide is not recommended. The low absorption makes it poor value despite the low sticker price.

What it is: Magnesium bound to threonic acid, a metabolite of vitamin C. Marketed under the brand name Magtein.

Absorption: Good systemic absorption, with a unique ability to cross the blood-brain barrier. A 2010 study in Neuron (by MIT researchers) found that magnesium threonate specifically increased magnesium concentrations in cerebrospinal fluid, while other forms did not.

Best for: Cognitive function, memory, focus. The theoretical basis is strong — boosting brain magnesium levels should support synaptic density and neuroplasticity. However, human clinical evidence is still limited. A 2016 study in Journal of Alzheimer's Disease showed some cognitive improvements in older adults, but it was small (44 participants) and sponsored by the patent holder.

Side effects: Generally well-tolerated. Some users report drowsiness or headache.

Typical dose: 1,500–2,000 mg of magnesium threonate per day (providing ~144 mg elemental magnesium). The elemental magnesium content is low, so it is often combined with another form.

Price in Australia: $0.50–1.50 per serve. The most expensive common form, partly due to the Magtein patent. Available from Life Extension, NOW Foods, and Thorne via iHerb and Amazon AU.

What it is: Magnesium bound to taurine, an amino acid concentrated in the heart, brain, and eyes.

Absorption: Good bioavailability. Taurine itself has cardiovascular benefits — a 2018 meta-analysis in Amino Acids associated taurine supplementation with reduced blood pressure.

Best for: Cardiovascular support, blood pressure management. The combination of magnesium and taurine provides complementary benefits for heart function. Less studied for sleep than glycinate.

Side effects: Well-tolerated, similar to glycinate.

Typical dose: 200–400 mg elemental magnesium per day.

Price in Australia: $0.20–0.60 per serve. Less common in Australian pharmacies; mostly available via iHerb and specialty retailers.

Here is how the five main forms stack up across the criteria that matter:

| Form | Absorption | Best For | GI Side Effects | AU Price/Serve |

|------|-----------|----------|-----------------|----------------|

| Glycinate | High | Sleep, anxiety, stress | Low | $0.10–0.50 |

| Citrate | High | General use, constipation | Moderate | $0.08–0.30 |

| Oxide | Low (4%) | Laxative only | High | $0.03–0.10 |

| Threonate | Good (crosses BBB) | Cognition, memory | Low | $0.50–1.50 |

| Taurate | Good | Heart health, BP | Low | $0.20–0.60 |

Our recommendation: For most Australians looking to supplement magnesium, glycinate is the best all-round choice. It has high absorption, minimal side effects, evidence for sleep and stress, and is available at reasonable prices (especially in powder form).

If you have constipation issues, citrate does double duty. If cognition is your primary concern and budget is not an issue, threonate has the most interesting (though limited) brain-specific research.

Avoid oxide unless you specifically want a laxative. The low absorption rate makes it poor value for actual magnesium supplementation.

Magnesium supplements are available from pharmacies (Chemist Warehouse, Priceline), health stores (Mr Vitamins, HealthPost), and online retailers (iHerb, Amazon AU, BulkSupplements).

Prices vary dramatically — the same 200mg dose of magnesium glycinate can cost $0.10/serve from BulkSupplements (powder) or $0.50+/serve from pharmacy brands (capsules). That adds up: a 90-day supply at $0.10/serve costs $9, versus $45+ for the expensive option.

Use SuppUp to compare current prices across 10+ Australian retailers for any magnesium product. We track prices from iHerb, Amazon AU, Chemist Warehouse, Mr Vitamins, HealthPost, BulkSupplements, Life Extension, Thorne, and more.