Medical Disclaimer: This article is for informational purposes only and does not constitute medical advice. Always consult your doctor or pharmacist before starting a supplement, especially if you take other medications.
Pick your magnesium form by your goal, not the milligrams on the label. Glycinate is gentle on the stomach and favored for sleep and stress. Citrate absorbs well and doubles as a mild laxative. Oxide is cheap but poorly absorbed. What you actually absorb depends on the form, not the dose printed on the bottle.
Why "500 mg" Means Different Things by Form
The number on the front of the bottle is the least useful part of it. That figure is how much magnesium the pill contains, not how much reaches your bloodstream, and those two numbers diverge wildly depending on the form.
A 2019 study in Nutrients put this plainly: it found that "the in vivo Mg bioavailability was not related to the Mg content of the supplements, but rather to the in vitro solubility and bioaccessibility." In other words, how much magnesium dissolves and becomes available matters far more than the raw milligrams. The same study confirmed that organic salts like citrate absorb better than inorganic magnesium oxide.
So a "500 mg" magnesium oxide tablet and a "200 mg" magnesium glycinate capsule can deliver a similar absorbed dose, because oxide gives up so little of what it holds. Chasing the biggest number on the shelf usually means buying the form your body uses least. Once you know that, the choice becomes about matching the form to what you actually want it to do.
The Magnesium Form Chart
| Form | Best for | Absorption | GI effect |
|---|---|---|---|
| Glycinate | Sleep, stress, daily topping up | Well absorbed | Gentle, least likely to loosen stools |
| Citrate | General replacement, mild constipation | Well absorbed | Mildly laxative |
| Oxide | Constipation relief, low cost | Poorly absorbed | Strongly laxative |
| Malate | Daytime use, general topping up | Well absorbed | Generally well tolerated |
| Threonate | Marketed for focus and cognition | Absorbed; brain claims are early | Generally gentle |
Two forms do the same job well from different angles. Glycinate and citrate both absorb well, so the deciding factor is your gut. Glycinate is the gentlest, which is why it wins for anyone taking magnesium daily or for sleep. Citrate absorbs just as well but pulls water into the intestine, so it doubles as a mild laxative, useful if constipation is part of the picture, annoying if it is not.
Glycinate: The Gentle All-Rounder
Magnesium glycinate is magnesium bound to glycine, an amino acid. That pairing does two things. It keeps absorption high, and it sidesteps the loose-stool problem that comes with cheaper forms.
That GI gentleness is the real reason glycinate dominates the sleep and daily-supplement conversation, not some dramatic absorption edge over citrate. In head-to-head terms, glycinate and citrate land in a similar absorption range. What sets glycinate apart is that you can take it every night without your gut complaining, which matters because magnesium's sleep benefit comes from consistent daily intake, not from a single well-timed dose. A form you tolerate nightly beats a form you take three times a week.
Citrate and Oxide: The Practical Trade-Off
Citrate is the workhorse. It absorbs well, it is inexpensive, and its mild laxative pull is a feature if you are constipated and a nuisance if you are not. For general magnesium replacement in someone with a regular gut, it is a reasonable default.
Oxide is where the milligram trap bites hardest. It carries a lot of elemental magnesium per pill and costs little, which is why bargain bottles love it. But the Nutrients study showed oxide sits at the bottom for bioavailability, so much of that impressive number passes straight through. Its main honest use is short-term constipation relief, where poor absorption and a laxative effect are actually the point. Taking too much of any form can cause problems, and our guide on too much magnesium covers the warning signs.
The Column Every Other Chart Skips: Drug Interactions
Picking a form is only half the decision if you take medication. Magnesium can interfere with how some drugs absorb, and that is true regardless of which form you choose.
The clearest example is thyroid medication. Magnesium can bind levothyroxine in your gut and blunt its absorption, which is why the two need to be spaced apart. Our guide on magnesium and levothyroxine covers the four-hour gap that keeps both working. Magnesium can also overlap with blood pressure medications in ways worth checking, which we lay out in taking magnesium with blood pressure medication. None of this rules magnesium out. It just means the conversation with your pharmacist should include your medication list, not only your goal.
How Pillo Helps
Once you have chosen a form, the whole benefit rides on taking it consistently, and on keeping it spaced from any medication it interacts with. That is two timing jobs at once, and both are easy to drop.
Pillo lets you schedule your magnesium and set a separate reminder for a medication like levothyroxine, so the gap between them stays intact instead of collapsing on a rushed morning. The persistent alarm keeps nudging until you confirm the dose, which turns "I should take magnesium daily" into an actual streak.
FAQ
Which magnesium form is best for sleep?
Glycinate is the usual choice for sleep, not because it absorbs dramatically better than citrate but because it is the gentlest on your stomach, which lets you take it consistently every night. Since magnesium's sleep benefit builds over time rather than from one perfectly timed dose, a form you tolerate nightly matters more than a marginal absorption edge.
Is magnesium oxide a waste of money?
Not entirely, but it is the wrong pick for most goals. The 2019 Nutrients study found oxide has poor bioavailability, so much of its high milligram count passes through unabsorbed. Its honest use is short-term constipation relief, where the laxative effect and low absorption are actually what you want. For daily supplementation, glycinate or citrate deliver more of what you pay for.
Does the milligram number on the bottle tell me how much I absorb?
No, and that is the most common mistake. The Nutrients research found absorption tracks with a form's solubility, not its magnesium content, so a big number on a poorly absorbed form like oxide can deliver less than a smaller number on glycinate or citrate. Read the form, not just the milligrams.
Can I take magnesium with my other medications?
Sometimes, but spacing matters for a few drugs. Magnesium can bind levothyroxine and reduce its absorption, so those need a four-hour gap, and it can overlap with blood pressure medications too. Bring your full medication list to your pharmacist before starting magnesium so any timing gaps get built in from the start.
What is the difference between magnesium glycinate and citrate?
Both absorb well, so the practical difference is your gut. Glycinate is bound to an amino acid and is the gentlest, making it the go-to for daily and bedtime use. Citrate absorbs just as well but has a mild laxative effect, which makes it better suited to general replacement or when you also want help with constipation.
This article provides general information about supplements and is not a substitute for professional medical advice. Always consult your doctor or pharmacist before starting magnesium, especially if you take other medications.
