There are dozens of magnesium supplements on the market. Most of them aren’t worth taking — not because magnesium doesn’t work, but because the form determines how much actually gets absorbed.
For most people taking magnesium daily, magnesium glycinate (bisglycinate) is the best choice. It absorbs well, sits gently in the stomach, and the glycine component adds sleep and relaxation benefits. But the right form depends on what you’re trying to address.
Here’s what the evidence shows for each major type.
Why the Form of Magnesium Matters
Not all magnesium reaches your cells. The key variable is bioavailability — how much gets absorbed through the gut rather than passing straight through.
Magnesium oxide, the most common form in cheap supplements, has bioavailability as low as 4% according to comparative studies. Chelated forms like glycinate and organic salts like citrate absorb significantly better — typically in the range of 50–80% depending on the form, dose, and your gut health.
The other practical factor is tolerability. Magnesium draws water into the intestines, which at high doses causes loose stools. Some forms do this far more than others — important if you’re taking it every day.
Main Forms Compared
| Form | Absorption | Best For | Laxative Effect |
|---|---|---|---|
| Magnesium glycinate | High | Sleep, anxiety, daily use | Minimal |
| Magnesium citrate | Moderate–High | Constipation, general use | Moderate |
| Magnesium malate | Moderate–High | Energy, muscle fatigue | Low |
| Magnesium threonate | High (brain-specific) | Cognitive health | Minimal |
| Magnesium oxide | Low (~4%) | Constipation, antacid | High |
| Magnesium sulphate | Variable | Epsom baths, IV use | High if oral |
Magnesium Glycinate
Magnesium glycinate — also called magnesium bisglycinate — is magnesium chelated to glycine, an amino acid. The chelated bond improves absorption and reduces how much unabsorbed magnesium reaches the colon, which is what causes the laxative effect in cheaper forms.
Glycine is also an inhibitory neurotransmitter with calming properties. It supports GABA activity in the brain, the same pathway involved in sleep onset and relaxation. A 2006 study in Sleep and Biological Rhythms found that glycine taken before bed improved sleep quality and reduced next-day fatigue.
This makes glycinate the preferred choice for sleep support, anxiety management, and long-term daily supplementation — particularly for anyone who has experienced digestive issues with other forms. Our Magnesium Glycinate provides 55mg elemental magnesium per capsule, vegan and UK-made with no artificial fillers.
Magnesium Citrate
Magnesium citrate is magnesium bound to citric acid. It’s highly water-soluble and absorbs efficiently. Research published in Magnesium Research (Walker et al., 2003) found citrate among the most bioavailable forms tested, comparable to glycinate for raising serum magnesium levels.
Its defining feature is its osmotic laxative effect — it draws water into the intestines. At low doses this is mild; at higher doses it can cause urgency. This makes it a good choice if constipation is a factor alongside magnesium deficiency, but less ideal for everyday use if digestive comfort matters.
Magnesium Malate
Magnesium malate is magnesium bound to malic acid, a compound found naturally in apples and other fruits. It absorbs well and causes less digestive disruption than citrate.
The malic acid component plays a role in the Krebs cycle — the process cells use to produce ATP energy. Some evidence suggests malate may be useful for people with fibromyalgia or chronic fatigue, where impaired energy production in muscles is a contributing factor. Research is limited but the rationale is sound.
Magnesium Threonate
Magnesium threonate (often sold under the brand name Magtein) is marketed for brain health, based on animal studies suggesting it crosses the blood-brain barrier more efficiently than other forms.
Human evidence is limited. A few small trials in older adults report modest cognitive improvements, but the research base is too thin to draw firm conclusions. It’s significantly more expensive than glycinate or citrate. For most people, that price premium isn’t yet justified by the evidence. See our full comparison in magnesium glycinate vs threonate.
Magnesium Oxide
Magnesium oxide is the most common form in budget supplements — and the least useful for correcting deficiency. Studies show bioavailability around 4%, versus 50–80% for chelated forms. Most of what you take acts as a bulk laxative rather than being absorbed.
Worth noting: several clinical trials concluding that magnesium “doesn’t work” for conditions like leg cramps used magnesium oxide. The null results may say more about the form than magnesium itself. See our analysis of the evidence in magnesium for leg cramps.
Magnesium Sulphate
Magnesium sulphate — Epsom salt — is used in baths or administered intravenously in hospitals for conditions like pre-eclampsia and severe hypomagnesaemia. Evidence for meaningful absorption through the skin is limited.
Oral magnesium sulphate acts as a strong laxative and is used in bowel prep formulas rather than as a daily supplement. It’s not the right choice for correcting a dietary shortfall.
Which Form Is Right for You?
For sleep and relaxation: Magnesium glycinate. Take 200–400mg of compound (providing roughly 50–110mg elemental) 1–2 hours before bed.
For constipation alongside deficiency: Magnesium citrate. The osmotic effect is useful here. Start low and adjust.
For muscle fatigue or fibromyalgia: Magnesium malate. Some evidence supports its role in energy metabolism in muscles.
For general daily use: Glycinate is the safest default. It doesn’t cause digestive disruption and the glycine adds a calming effect that’s useful for most people over 40.
For brain health: The evidence for threonate is preliminary. Glycinate remains the more practical choice until larger trials establish a clearer benefit.
What to Check on the Label
Look for the elemental magnesium content, not just the compound weight. A 500mg capsule of magnesium glycinate contains roughly 100mg of elemental magnesium — the rest is glycine.
The NHS recommends 270mg/day for women and 300mg/day for men of total magnesium from all sources. The EU’s tolerable upper intake for supplemental magnesium is 250mg elemental per day from supplements alone.
Blood tests for magnesium are often unreliable because most is stored in bones and cells rather than the bloodstream. Symptoms are often a more useful guide: persistent fatigue, poor sleep, muscle cramps or twitching, and heightened anxiety are all associated with low magnesium. See our full guide to magnesium benefits for more on deficiency signs.
FAQ
Q: What is the best form of magnesium to take?
A: For most people, magnesium glycinate is the best daily form. It absorbs well, is gentle on digestion, and the glycine component supports sleep and relaxation. Magnesium citrate is a better option if constipation is a factor.
Q: Is magnesium glycinate the same as magnesium bisglycinate?
A: Yes — both names refer to the same compound. The “bis” prefix indicates that two glycine molecules are bound to each magnesium ion. Manufacturers use the terms interchangeably.
Q: Which form of magnesium is best absorbed?
A: Chelated forms like glycinate and organic salts like citrate have the highest absorption — typically 50–80%. Magnesium oxide has very poor absorption, around 4%, making it largely ineffective for correcting deficiency.
Q: Can I take magnesium glycinate and citrate together?
A: You can, but it’s rarely necessary. If you want citrate’s digestive benefits alongside glycinate’s sleep support, taking them at different times of day makes sense. Start with one form first to assess how your body responds.
Q: How long does it take to feel the effects of magnesium?
A: For digestive effects, citrate can work within hours. For sleep, stress, and muscle benefits, consistent use over 2–4 weeks is typically needed. Magnesium works by correcting a chronic shortfall, not as a single-dose fix.
References
- Coudray C, et al. (2005). Study of magnesium bioavailability from ten organic and inorganic Mg salts in Mg-depleted rats. Magnesium Research, 18(4), 215–223.
- Walker AF, et al. (2003). Mg citrate found more bioavailable than other Mg preparations in a randomised, double-blind study. Magnesium Research, 16(3), 183–191.
- Inagawa K, et al. (2006). Subjective effects of glycine ingestion before the sleep period on sleep quality. Sleep and Biological Rhythms, 4(1), 75–77.
- Abbasi B, et al. (2012). The effect of magnesium supplementation on primary insomnia in elderly. Journal of Research in Medical Sciences, 17(12), 1161–1169.
- NHS. Vitamins and minerals — Magnesium.
This article is for informational purposes only and does not constitute medical advice. Always consult a qualified healthcare professional before starting any supplement, especially if you are pregnant, have a medical condition, or take prescription medication.
