Which Magnesium? A Guide to Choosing the Right Form
Supplements · Choosing well
There are a dozen kinds on the shelf. Only two differences between them actually matter.
Written for my patients. If you are not one, read "call me" as "call your own clinician", and take the questions here to them.
The magnesium aisle has gotten out of hand. Oxide, citrate, glycinate, malate, taurate, threonate, orotate. Bottles promising sleep, calm, regularity, fewer cramps, a sharper memory. Different prices, different claims, and almost all of it marketed as if the form were the whole story.
It is not. Strip away the marketing and the forms differ in two ways: how much of the magnesium actually gets into you, and what the rest of it does to your bowels. Those two things explain nearly every recommendation on this page.
This is a guide to choosing, not a recommendation to start. Whether you need magnesium at all is a separate conversation, and it is one worth having.
The two things that separate them
Everything else you will read on a label, whether chelated, brain-bioavailable, ionic or picometer, is either a restatement of absorption or a claim with very little behind it.
How much you actually need
| Amount | |
|---|---|
| From everything you eat and take, per day | Women 310–320 mg · Men 400–420 mg |
| Ceiling on supplements alone, per day | 350 mg |
| Ceiling on magnesium from food | None |
The 350 mg ceiling exists because higher doses cause diarrhea, not because magnesium turns dangerous there. Migraine prevention deliberately goes above it, which is why that use belongs under supervision.
One more thing worth knowing: a standard blood magnesium level is a rough instrument. Most of your magnesium sits in bone and inside cells, and your body works hard to keep the blood number steady, so it can read normal while your stores are running low. A normal result is reassuring. It is not proof.
And one correction. Glycinate is the best tolerated form, but it is not proven to be the best absorbed, whatever the label says. The one head-to-head trial that compared citrate against an amino acid chelate over sixty days favored citrate. Tolerance is a good enough reason to choose glycinate. Absorption is not one.
Every form on the shelf
| Form | Absorbed · bowels · what it is for |
|---|---|
| Oxide ≈60% Mg | Poor absorption · strong on the bowels. Constipation. Cheapest form, most magnesium per pill, least of it absorbed. Also the form used in most migraine studies. Softer, more frequent stools within a day or two is the intended effect. Because so little is absorbed, do not expect changes in energy, sleep, or cramps from it. |
| Citrate ≈16% Mg | Good absorption · mild to moderate. The workhorse, and the best studied of the well-absorbed forms. Raising a low level, migraine prevention, and a gentler option than oxide for constipation. If your level was low, improvements show up over four to twelve weeks, not days. |
| Glycinate ≈14% Mg | Good absorption · minimal. For raising a low level when other forms send you to the bathroom, and the usual choice for evening use. Many people report feeling calmer at bedtime, which is a common experience in practice and has not been tested against other forms in a trial. |
| Chloride ≈12% Mg | Good absorption · moderate. Usually comes as a liquid, oil, or spray. The sprays commonly cause tingling on the skin; that is salt on skin, not evidence of absorption, which has not been shown through skin in any meaningful amount. |
| Malate ≈15% Mg | Good absorption, limited data · mild. Marketed for fatigue. Malate is part of the body's energy-production cycle, which is where that claim comes from, and it has not been borne out in good trials. |
| Taurate ≈9% Mg | Likely good, little data · minimal. Marketed for blood pressure. Taurine on its own has some evidence for modestly lowering blood pressure, and the combination is reasonable in theory, but it has barely been tested. |
| L-threonate ≈8% Mg | Good absorption · minimal. Marketed for memory. The one placebo-controlled trial in adults found a modest improvement in cognitive testing over six weeks and no improvement in sleep. A poor choice for raising a low body level, and the most expensive form on the shelf. |
| Gluconate, lactate ≈6–12% Mg | Good absorption · mild. Inexpensive and well tolerated, just less commonly stocked. |
| Orotate, aspartate ≈7–15% Mg | Good absorption · mild. The performance and heart claims rest on small, old studies that have not been repeated. |
| Sulfate (Epsom salt) ≈10% Mg | Poor by mouth · strong. For baths. Most of what a bath does is the hot water; absorption through skin is unproven. Swallowed, it causes fast, forceful diarrhea with real risk of dehydration. Not a routine laxative. |
What the evidence actually supports
Well supported
Mixed or modest
Weak or unproven
How to take it
- Read the label for elemental magnesium, not the weight of the compound. A capsule listing 500 mg of magnesium citrate does not contain 500 mg of magnesium; it contains closer to 80.
- Split the dose. Two smaller doses absorb better than one large one, and they are far easier on your stomach. Take it with food.
- Start at about 200 mg and build over two weeks. There is no prize for starting high.
- Loose stools mean you are above your dose, not that the product is bad. Cut back, or switch to glycinate.
- If one form bothers you, change forms before you give up on magnesium.
- For migraine, give it at least eight to twelve weeks before deciding it did not work.
Timing around your medications
The one real safety limit
Food first, where you can
| Food | Magnesium, approximate |
|---|---|
| Pumpkin seeds, 1 oz | 156 mg |
| Chia seeds, 1 oz | 111 mg |
| Almonds, 1 oz | 80 mg |
| Spinach, cooked, ½ cup | 78 mg |
| Cashews, 1 oz | 74 mg |
| Black beans, cooked, ½ cup | 60 mg |
| Edamame, shelled, ½ cup | 50 mg |
| Dark chocolate, 1 oz | 50 mg |
| Brown rice, cooked, ½ cup | 42 mg |
| Avocado, ½ cup | 22 mg |
Where this leaves you
Magnesium is cheap, it is safe if your kidneys work, and running low on it is genuinely common. That is a reasonable set of conditions for trying something. It is not a reason to expect it to fix four unrelated problems at once.
Most people arrive at magnesium having read that it handles sleep, cramps, anxiety, and constipation together. The evidence is strong for one of those, reasonable for another, and thin for the rest. Knowing which is which is what keeps you from spending a year on the wrong bottle.
And if you take it properly for three months and nothing changes, that is information too. It usually means magnesium was not the missing piece, and something else has been asking for attention. That is the more interesting conversation, and the one I would rather have with you.
The short version
- Constipation, and you want it to work on the gut: oxide.
- Raising a low level, or migraine prevention: citrate.
- Anything upsets your stomach, or you are taking it at night: glycinate.
- Everything else on the shelf: interesting, not established.
I wrote this for my patients, and it reads the same for everyone: general information, not a plan. If you would like your own numbers read against your own story, that is what a Lab Second Look is for. If you are not sure where to start, the free intro call is fifteen minutes.
A note on how to use this. General education, not individualized medical advice, and not a recommendation to start any supplement. Doses and food values are approximate and vary by product. Do not start magnesium without speaking to your clinician if you have reduced kidney function, heart block or a slow heart rate, myasthenia gravis, are pregnant, or take bisphosphonates, thyroid medication, diuretics, or antibiotics. Supplements are not reviewed by the FDA for effectiveness before sale.
- Firoz M, Graber M. Bioavailability of US commercial magnesium preparations. Magnes Res 2001;14(4):257–62.
- Walker AF et al. Mg citrate found more bioavailable than other Mg preparations in a randomised, double-blind study. Magnes Res 2003;16(3):183–91.
- Blancquaert L et al. Predicting and testing bioavailability of magnesium supplements. Nutrients 2019;11(7):1663.
- Chang L et al. AGA–ACG clinical practice guideline: pharmacological management of chronic idiopathic constipation. Am J Gastroenterol 2023;118(6):936–54.
- Mori S et al. A randomized double-blind placebo-controlled trial on the effect of magnesium oxide in patients with chronic constipation. J Neurogastroenterol Motil 2019;25(4):563–75.
- Holland S et al. Evidence-based guideline update: NSAIDs and other complementary treatments for episodic migraine prevention in adults. Neurology 2012;78(17):1346–53.
- Garrison SR et al. Magnesium for skeletal muscle cramps. Cochrane Database Syst Rev 2020;(9):CD009402.
- Mah J, Pitre T. Oral magnesium supplementation for insomnia in older adults: systematic review and meta-analysis. BMC Complement Med Ther 2021;21(1):125.
- Lopresti AL, Smith SJ. The effects of magnesium L-threonate on cognitive performance and sleep quality in adults. Front Nutr 2026;12:1729164.
- NIH Office of Dietary Supplements. Magnesium: Fact Sheet for Health Professionals.
Trang Ca Laube, FNP-BC, FMACP · Reclaim Power Telehealth · Updated September 2026
Reclaim Power Telehealth works alongside your primary care team, not instead of it. It is not a replacement for urgent or emergency care. If something is acute, call your doctor or 911.
© Reclaim Power Telehealth · Telehealth in Indiana, Colorado, Arizona, Washington and Utah · English and Vietnamese
