Magnesium citrate is magnesium bound to citric acid. Of the forms that absorb well, it’s usually the cheapest, which makes it the sensible default if what you want is simply more magnesium. The US National Institutes of Health lists citrate among the forms that dissolve well and are better absorbed than magnesium oxide.
It has one quirk worth knowing before you buy: at higher doses it loosens the bowels. That is either the reason you’re buying it or the reason you’ll want to keep the dose sensible. More on that below.
Why it absorbs better than oxide
Citric acid is an organic acid, and magnesium bound to one dissolves more readily in the gut than magnesium bound to an inorganic compound like oxide. A comparison of commercial preparations found citrate more bioavailable than oxide, and the NIH makes the same general point: forms that dissolve well tend to be absorbed better.
That matters at the till. Oxide is cheap and turns up on a lot of labels, but much of it passes straight through you. Citrate costs slightly more and delivers considerably more usable magnesium per dollar.
Muscle tension and cramps
This is where citrate has its own small evidence base rather than borrowing magnesium’s in general.
A randomised, double-blind, cross-over trial gave 46 people with persistent night-time leg cramps 300mg of magnesium as citrate for six weeks. Counting cramps in a diary, the magnesium arm came out better, but not by enough to rule out chance (p=0.07). What did reach significance was how people felt about it: 78% thought the magnesium had helped, against 54% for placebo (p=0.03).
Read fairly, that cuts both ways. The objective measure missed the mark, which is why the 2020 Cochrane review on magnesium for cramps remains unimpressed overall. But this is one of the few trials done on citrate specifically, the direction of travel favoured magnesium, and the people taking it noticed something. If you get ordinary night cramps, a six-week trial of citrate is cheap and low-risk. Just go in expecting a possible improvement rather than a cure.
The nervous system angle
Magnesium acts as a natural blocker at NMDA receptors, which are part of how nerve cells fire. Block them a little and neuronal excitability comes down. That mechanism is the reason magnesium keeps being studied for things involving an overexcited nervous system: muscle twitches, anxiety, migraine.
Two caveats stop this being a headline. The mechanism is magnesium’s, not citrate’s specifically, so any well-absorbed form gets you the same thing. And a plausible mechanism is not the same as a proven benefit; the trials in humans are mixed, as the anxiety page sets out. Citrate delivers magnesium efficiently, which is all you can fairly claim for it here.
If calm is your main goal rather than a happy side effect, glycinate suits it better. Glycine is mildly calming in its own right, and glycinate won’t send you to the bathroom.
Constipation, and the dose that causes it
The laxative effect is real and worth planning around. Magnesium that isn’t absorbed draws water into the bowel, which softens things and gets them moving. Pharmacies sell citrate for exactly this, at doses well above what you’d take as a supplement.
For occasional constipation, that’s a feature. If you’re taking citrate for the magnesium and not the bathroom trip, keep the dose modest and split it across the day rather than swallowing it all at once. Most people find a comfortable level fairly quickly.
Needing a laxative most weeks is a different problem. That deserves a doctor’s opinion rather than a standing supplement habit.
Dosing basics
Read the elemental magnesium per serving, not the total compound weight. Citrate is a bulky molecule, so a 1,000mg tablet delivers nothing like 1,000mg of usable magnesium. The number on the back is the only one worth comparing between products.
Start low and increase only if you need to. Loose stools are the signal you’ve overshot, and with citrate that signal arrives sooner than with gentler forms.
The usual cautions
The same three groups, on every page, because they matter every time. If your kidneys don’t work well, magnesium supplements can be risky, because the kidneys are what clear it: talk to a doctor first. If you take regular medication, magnesium interacts with several drugs, including some antibiotics, and a pharmacist can check yours in about a minute. If you’re pregnant or breastfeeding, ask your midwife or doctor before starting anything.
What to look for when buying
- Elemental magnesium per serving, stated plainly.
- How many capsules make a serving. Bulky forms often need two or three, which changes the real cost per day.
- No oxide padding the blend. Some cheaper products mix in magnesium oxide to lift the headline number without adding much you can use.
- A short ingredient list. For a commodity form like this there’s no reason for a long one.
The full checklist is in the buying guide.
Common questions
Is citrate better than glycinate? Different jobs. Citrate is cheaper and absorbs well, so it’s the value pick for raising your magnesium. Glycinate is gentler on the stomach and better suited to sleep and stress.
Will it help my cramps? Possibly, and the trial above is the fairest guide: worth six weeks, not worth strong expectations.
Will it upset my stomach? It might at higher doses. That’s the trade-off for the price. If your digestion is sensitive, glycinate is the safer choice.
Can I take it every day? Many people do, within the suggested dose. Check with a professional if you have a health condition or take medication.
Sources: NIH Office of Dietary Supplements: Magnesium Fact Sheet (https://ods.od.nih.gov/factsheets/Magnesium-HealthProfessional/); Roffe et al., randomised, cross-over, placebo-controlled trial of magnesium citrate in chronic persistent leg cramps, Medical Science Monitor, 2002 (https://pubmed.ncbi.nlm.nih.gov/12011773/); magnesium citrate found more bioavailable than oxide or amino-acid chelate, Walker et al., Magnesium Research, 2003 (https://pubmed.ncbi.nlm.nih.gov/14596323/); bioavailability of US commercial magnesium preparations, Firoz & Graber, Magnesium Research, 2001 (https://pubmed.ncbi.nlm.nih.gov/11794633/)
This article is general information, not medical advice.