Magnesium is not one supplement. It is at least seven, and the counter-ion the mineral is bound to changes almost everything about how it acts in your body — where it absorbs, whether it moves loose stool, whether it crosses into the brain, whether it wastes calories on the way through.
The companion piece on magnesium glycinate covers the default form for sleep, anxiety, and general repletion. This piece is the map for everything else. When citrate is the right choice. When threonate earns its price. When to layer forms. And the oxide-padding trick that makes cheap blends look strong on the label while delivering almost nothing to your tissues.
Read this before you buy your second bottle.
The elemental magnesium problem, in one paragraph
Every magnesium supplement is a compound. The mineral itself makes up only a fraction of the total weight. That fraction — called the elemental magnesium percentage — is what actually interacts with your physiology. The rest is the counter-ion. A label reading "Magnesium Citrate 1000 mg" describes the compound weight; the elemental magnesium is roughly 160 mg. If the elemental number is not printed on the label, the brand does not want you doing the arithmetic.
Here are the elemental percentages you need to memorize:
- Magnesium oxide: ~60 percent elemental. Absorption ~4 percent. Highest math, lowest delivery.
- Magnesium chloride: ~12 percent elemental. Absorption moderate to good.
- Magnesium citrate: ~16 percent elemental. Absorption ~25 to 30 percent.
- Magnesium malate: ~11 percent elemental. Absorption reasonably good.
- Magnesium glycinate (bisglycinate): ~14 percent elemental. Absorption very good, gentle on gut.
- Magnesium taurate: ~9 percent elemental. Absorption good.
- Magnesium orotate: ~7 percent elemental. Absorption modest.
- Magnesium L-threonate: ~8 percent elemental. Absorption modest, but the point is CNS penetration, not systemic dose.
Oxide has the highest elemental content on paper. It also has the worst absorption. This is the padding trick — brands blend a small amount of glycinate or citrate with a large amount of oxide and market the combined elemental number. You get the label. Your tissues get about four percent of it.
Magnesium citrate: the constipation-and-migraine workhorse
Citrate is the second most-studied form after glycinate. It is cheap, well-absorbed (~25 to 30 percent), and mildly laxative at doses above 300 mg elemental.
The laxative effect is not a bug. If constipation is the problem you are solving, citrate is the tool. Osmotic action pulls water into the colon. Effective, gentle, non-habit-forming. Bowel-prep clinics have used higher-dose citrate for decades.
Citrate is also the form most often used in migraine-prevention trials. Multiple RCTs at 400 to 600 mg elemental per day show 40 to 50 percent reduction in migraine frequency after eight to twelve weeks. The American Academy of Neurology lists magnesium as a Level B (probably effective) preventive.
Use citrate if: you deal with constipation, or you are prophylaxing migraines and can tolerate the mild GI effect.
Avoid citrate if: you already run loose, or you need a form to take right before bed and would rather not walk to the bathroom at 2 am.
Magnesium L-threonate: the one that crosses the blood-brain barrier
Threonate is the newest common form, and the most expensive. The reason it exists is a single 2010 MIT study (Slutsky et al.) showing that a specific threonate salt raised brain magnesium levels in rats where other forms did not. The compound was developed as Magtein and patented.
Human data is thinner than the marketing suggests. A 2016 Liu et al. trial in older adults with cognitive complaints showed improvement on some memory measures at 1500 to 2000 mg of Magtein per day (roughly 144 mg elemental). A 2022 trial from the same group showed similar signal. Effect sizes are modest, sample sizes are small, and both trials had industry ties.
What threonate is not: a general-purpose magnesium supplement. The elemental dose is low. If you are threonate-only, you are still magnesium-deficient systemically.
Use threonate if: cognition and memory are the specific goal, and you can afford $40 to $60 a month. Layer it with a cheaper form for systemic repletion.
Avoid threonate if: you want boring, well-evidenced sleep and anxiety support. Glycinate is stronger there and one-fifth the price.
Magnesium malate: the daytime and muscle-pain form
Malate is magnesium bound to malic acid, an intermediate in the Krebs cycle. The theoretical case: malic acid contributes to ATP production, so pairing it with magnesium supports energy metabolism at the mitochondrial level.
Evidence is modest. A small 1995 trial (Abraham and Flechas) in fibromyalgia patients showed reduced tender-point pain at 300 to 600 mg malate per day. Follow-up work has been mixed. A 2013 trial by Russell et al. did not show a significant benefit over placebo.
Clinical use has stuck around mostly for two reasons: it is slightly stimulating rather than calming, so it fits into morning stacks; and some fibromyalgia patients report it works when nothing else does.
Use malate if: you want a daytime magnesium, or you are working with chronic muscle-pain conditions.
Avoid malate if: sleep is your goal. Glycinate at bedtime does that job.
Magnesium oxide: what it is for, and what it is not
Oxide is cheap, high in elemental magnesium by weight, and roughly four percent absorbed. Almost none of what you swallow reaches systemic circulation.
This does not make it useless. It makes it single-purpose. The un-absorbed magnesium sits in the gut and pulls water into the colon — that is why oxide is the active ingredient in Milk of Magnesia. It is a laxative first and a supplement second.
The problem is how oxide gets used. Cheap multivitamins and mass-market "high-strength" magnesium blends pad the label using oxide. "1000 mg per serving" reads as strong. In practice, if 800 mg of that is oxide, you are absorbing about 32 mg elemental. That is a fifth of what a well-dosed glycinate gives you.
Use oxide if: you specifically need an occasional bowel-clearing dose, or you understand exactly what you are buying and want the cheapest laxative on the shelf.
Avoid oxide if: your goal is systemic repletion. It is almost always the wrong form.
Magnesium taurate: the cardiovascular pick
Taurate is magnesium bound to taurine, an amino-acid-like compound with independent cardiovascular signal. Taurine has its own literature — modest blood-pressure reduction, some antiarrhythmic effect, improvement in heart-failure metrics in small trials.
The pairing is theoretically synergistic. In practice, magnesium taurate has less direct RCT data than glycinate or citrate. Most of the case for taurate is inference from separate magnesium and taurine literatures.
Cardiologists who use it clinically usually dose 200 to 400 mg elemental per day, often layered with CoQ10, potassium, and B vitamins in a cardiac-support stack.
Use taurate if: blood pressure or palpitations are the primary goal, and you already have a solid workup ruling out other causes.
Avoid taurate if: you are chasing a general supplement — glycinate does the same magnesium job for less money.
Magnesium orotate: the athletic-performance niche
Orotate is magnesium bound to orotic acid. Cell biologists know orotic acid as a precursor to pyrimidine nucleotides. The claim is that orotate acts as a carrier that helps deliver magnesium into cardiac and skeletal muscle cells, where those nucleotides are actively used.
The evidence base is small but interesting. A 2009 Classen trial in patients with congestive heart failure showed improved survival at 6000 mg orotate per day over one year. A 1998 Zeana trial in trained athletes showed modest performance improvement. Not enough to overturn glycinate as a default, enough to consider it a niche pick for endurance athletes and cardiac-rehab patients.
Use orotate if: you are an endurance athlete willing to experiment, or working under a cardiologist who specifically recommends it.
Avoid orotate if: you are a general user. Expensive, thinly-studied, no clear advantage over cheaper forms for most goals.
Magnesium chloride and sulfate: the topical question
Chloride is the form in "magnesium oil" sprays. Sulfate is the form in Epsom salts. Both are marketed as transdermal — magnesium absorbed through the skin, bypassing the gut entirely.
The transdermal claim is largely mythology. A 2017 review by Gröber et al. found essentially no controlled evidence that meaningful serum magnesium changes result from topical application. Serum magnesium is tightly regulated by the kidney, and skin is an effective barrier to charged mineral ions.
An Epsom-salt bath is relaxing. That relaxation is likely thermal and behavioral, not pharmacological. If a warm bath before bed helps you sleep, keep taking the bath. Do not count on it for magnesium repletion.
Oral magnesium chloride, on the other hand, absorbs reasonably well. It is just uncommon on shelves in single-form oral products.
When to layer forms
Some practitioners prescribe multi-form blends. The theory is that different forms preferentially reach different tissues — glycinate for nerves, taurate for heart, threonate for brain, malate for muscle. The evidence for tissue-specific preference is weaker than the marketing suggests, but the practical case for blends is that they let you cover several goals with one bottle.
A defensible layering strategy for someone with multiple goals:
- Morning: 200 mg elemental magnesium malate. Daytime energy, no drowsiness, mild support for muscle recovery.
- Evening: 200 mg elemental magnesium glycinate. Sleep, anxiety, general repletion.
- Optional add-on: 144 mg elemental Magtein (threonate) with dinner, if cognition is a specific priority and budget allows.
Total elemental target: 300 to 400 mg per day. Titrate slowly. Loose stool means back off.
The oxide-padding trick, one more time
This is the single most important thing to check on any magnesium label. Some brands list two or three forms on the front of the bottle — "Magnesium Complex: Glycinate, Citrate, Oxide" — and pad the total elemental number using oxide because oxide is so much cheaper than the other two.
If a supplement facts panel lists magnesium oxide anywhere in the top three ingredients by weight, assume the total elemental number on the label overstates what is actually absorbed by a factor of two or three. A blend that reads "400 mg elemental magnesium" on the front but is 60 percent oxide by weight is delivering closer to 150 mg systemically.
The fix is boring. Choose products that either name one high-quality form on the label (glycinate, citrate, malate, taurate, threonate) or that list every form's elemental contribution separately. If oxide appears at all, it should be a small tail, not a load-bearing ingredient.
The honest summary
For most people asking "which magnesium," the answer is still glycinate — cheap, well-evidenced, gentle, works for sleep and anxiety. Read the glycinate deep-dive linked at the top.
For the specific goals below, the rest of the map matters:
- Constipation or migraine prevention: citrate, 200 to 400 mg elemental daily.
- Cognition and memory support: L-threonate (Magtein), 144 mg elemental daily, layered with a cheaper form for systemic dose.
- Daytime energy or fibromyalgia: malate, 200 to 400 mg elemental daily, morning.
- Cardiovascular focus: taurate, 200 to 400 mg elemental daily, ideally coordinated with a clinician.
- Endurance-athletic: orotate, at dose ranges from published trials (2000 to 6000 mg compound weight).
- Bowel prep: oxide, understanding you are buying a laxative.
The other rules stay the same. Read the elemental number, not the compound number. Skip oxide-padded blends unless oxide is what you specifically want. Start low, titrate up, back off on loose stool. And remember that half of US adults are below the RDA on dietary magnesium — pumpkin seeds, spinach, almonds, black beans, and dark chocolate will move you a long way toward 400 mg per day without any pills at all.
Supplement second. Diet first.