Which magnesium for what, what two forms really differ by, and the number almost no label prints: how much of that 500 mg capsule is actually magnesium.
Magnesium glycinate · 500 mg × 1
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For sleep and stress, the sources name
| Form | Magnesium by weight | In a 500 mg capsule | Absorption |
|---|
This is not medical advice and it does not diagnose anything. Magnesium interacts with some prescriptions, and a high intake matters if your kidneys do not work normally — talk to your doctor or pharmacist before you start.
A 500 mg magnesium glycinate capsule contains about 70 mg of magnesium. A 500 mg magnesium oxide tablet contains about 302 mg. Both labels say “500 mg”, and almost none of them prints the number that matters — so this page works it out from each compound’s own chemistry, then shows which forms the medical sources actually name for what you want it for.
How to use it
Pick what you want magnesium for and the page lists only the forms whose sources name that use, with their own words quoted, best-absorbed first. Then type what your bottle says — the form and the milligrams per serving — and you get the elemental magnesium, what share of the recommended daily amount that covers for your age and sex, and whether it sits under the 350 mg a day upper limit for supplements. If your label already says “elemental magnesium”, tick the box and nothing is converted.
The number no label gives you: elemental magnesium
Magnesium is never sold on its own. It is bound to something — an oxide, a citrate, a glycinate — and the weight on the front of the bottle is usually the whole compound. How much of that is magnesium is fixed by the formula and by nothing else:
- Magnesium oxide (MgO) — 60.3% magnesium. A 500 mg tablet is about 302 mg of magnesium, which is why it is the cheapest way to hit a big number on a label, and also why it is the form the sources call poorly absorbed.
- Magnesium citrate — 16.2%. A 500 mg dose gives about 81 mg.
- Magnesium glycinate — 14.1%. A 500 mg dose gives about 70 mg.
- Magnesium L-threonate — 8.3%. A 500 mg dose gives about 41 mg, which is why threonate products are dosed in grams.
Those percentages are arithmetic from the standard atomic weights, not a claim anyone made, and a test recomputes every one of them each time this page is built. They tell you nothing about absorption — a well-absorbed 14% and a poorly absorbed 60% can end up anywhere relative to each other — which is exactly why the table shows both columns side by side instead of ranking forms by one of them.
How much you need, and where the ceiling is
The recommended daily amounts (MedlinePlus, from the Dietary Reference Intakes) are 400–420 mg for men and 310–320 mg for women, rising with age at 31; in pregnancy, 350–400 mg. That is total magnesium, food included, and most of it is meant to come from food.
The ceiling is a different number for a different thing. The Tolerable Upper Intake Level is 350 mg a day of supplemental magnesium — “the highest level of daily supplemental magnesium intake likely to pose no risk of diarrhea or gastrointestinal disturbance in almost all individuals” (Linus Pauling Institute, Oregon State University). It applies only to what you take, not to what you eat, and this page will never suggest going past it. MedlinePlus adds the part that matters most: side effects from a high intake are uncommon “except in people with significantly reduced kidney function”.
Where the sources disagree — and where they are quiet
Both sources used here call citrate, glycinate, malate, lactate and L-threonate well absorbed, and both call oxide poorly absorbed. Neither states an absorption for taurate, so this page says “not stated” rather than guessing. Magnesium chloride, orotate, aspartate, gluconate and hydroxide appear in only one of them, so they are left out of the goal lists entirely: one source is not a rule. That is a deliberately smaller table than most pages on this subject, and it is the reason to trust the rows that are in it.
Common mistakes
- Comparing bottles by the big number. “High strength 500 mg” tells you what the capsule weighs, not what you absorb.
- Counting food against the 350 mg limit. The limit is for supplements only.
- Taking oxide for sleep because it is the cheapest. It is the form both sources call poorly absorbed, and the one used as a laxative.
- Assuming a gentle form is a small dose. Glycinate is gentle because of the glycine, not because the dose is low.
Frequently asked questions
What is the best type of magnesium?
There is no single best one, and any page that names one without saying “for what” is guessing. For sleep and stress the sources here name glycinate; for constipation, oxide and citrate; for memory and mood, L-threonate; for blood pressure, taurate; for a sensitive stomach, glycinate, malate or lactate.
Magnesium glycinate vs citrate — which should I take?
Both are called well absorbed. Citrate has a laxative effect that glycinate does not, which makes citrate the better one if constipation is the problem and the worse one if it is not. By weight, citrate is 16.2% magnesium and glycinate 14.1%, so the difference in what you swallow is small next to the difference in what it does to your gut.
How much magnesium should I take?
The recommended daily total is 310–320 mg for women and 400–420 mg for men, from food and supplements together, and supplements themselves have a 350 mg a day ceiling. Where you sit between those depends on what you already eat, which is a question for your doctor or a dietitian rather than a calculator.
When should I take magnesium?
Neither source read here states a required time of day. Glycinate is the form named for sleep, which is why people take it in the evening. If a form upsets your stomach, taking it with food is the usual answer.
How much magnesium is in a 500 mg capsule?
Between about 41 mg and 302 mg, depending entirely on the form: threonate 41 mg, taurate 45 mg, lactate 60 mg, glycinate 70 mg, malate 78 mg, citrate 81 mg, sulfate 101 mg, oxide 302 mg.
Can I take too much magnesium?
From supplements, yes — past 350 mg a day the usual result is diarrhoea and stomach upset. It matters far more if your kidneys do not work normally, and magnesium interacts with some prescriptions, so ask your pharmacist before you add it to anything.
Read next
- The best nootropic for brain fog — where magnesium usually appears in a stack.
- Do nootropics help with memory?
- My top three nootropic supplements, bought and taken for four weeks each.
This is not medical advice, and nothing here diagnoses or treats anything. Talk to your doctor or pharmacist before starting a supplement — especially if you take blood thinners, antidepressants or blood-pressure medication, or if you have kidney problems.