Magnesium Glycinate Side Effects: The Ceiling Is 350 mg and Night Work Uses 275 of It

Magnesium glycinate side effects are gastrointestinal: loose stools or an unsettled stomach, tracking dose and form. The tolerable upper intake level for supplemental magnesium is 350 mg a day, per the NIH Office of Dietary Supplements. TARE’s Night Work supplies 275 mg elemental, confirmed in writing by its manufacturer on 27 August 2026 and never measured on a certificate.

Two things on this page cost us money to print, so they go at the top rather than the bottom.

The first: in the newest head-to-head absorption trial, the form we sell was the one that did not move the number. That trial has two serious caveats and both are set out below. It is still published here, in full, because a brand that quotes the one favourable trial and hides the unfavourable one has told you nothing you can use.

The second: at 275 mg, Night Work uses most of the ceiling. The upper limit for supplemental magnesium is 350 mg a day. Three capsules leave 75 mg of room, and a multivitamin or a greens powder can eat that without ever announcing it. Nobody selling magnesium has an incentive to tell you that, which is exactly why it is the second paragraph.

The short version, effect by effect

Every row below is expanded further down with its sample size, its population and its funding attached. Read the table for the shape and the sections for the caveats, because on this subject the caveats are most of the content.

Does magnesium glycinate upset your stomach?

It can, and when magnesium does it is usually the form and the amount rather than the person. The NIH Office of Dietary Supplements records that magnesium is a primary ingredient in some laxatives — a tablespoon of one supplies 500 mg of elemental magnesium as magnesium hydroxide — and that some of that magnesium is not absorbed because of the laxative effect. Form decides what magnesium does on the way through.

That single fact explains most of what people call a magnesium side effect. Milk of magnesia is sold as a laxative and its directions run to four tablespoons a day — a dose the Office of Dietary Supplements notes is well above the safe upper level, and which it says is not fully absorbed because of the laxative effect. The pairing is the point: the salt that moves the bowel and the salt that absorbs poorly are the same salt.

So the practical version, in three lines:

• Bowel looseness is the effect that scales with the amount. It is the same action a magnesium laxative is sold for, at a smaller dose.
• An unsettled stomach on an empty one usually answers to food.
• Less at a time is the fix when the other two do not work.

None of that is unique to glycinate. It is the behaviour of magnesium in general, modulated by which salt it arrives as.

Why is glycinate the form usually chosen for tolerability?

Because oxide and sulfate are the documented laggards on absorption, and magnesium in laxative form is a known gastrointestinal actor. The trial most often cited for glycinate — JPEN 1994, in patients with ileal resection — found glycinate at 23.5% against oxide at 11.8% only in the subgroup with the most impaired absorption. In the patient group as a whole the two tied: 23.5% against 22.8%.

Two sources sit behind that answer and it is worth separating them, because they are routinely welded together into a claim neither one makes.

The first is the NIH Office of Dietary Supplements, which states that forms of magnesium dissolving well in liquid are more completely absorbed than less soluble forms, and that magnesium in the aspartate, citrate, lactate and chloride forms is absorbed more completely and is more bioavailable than magnesium oxide and magnesium sulfate. Read that list again: glycinate is not on it. Anyone quoting that sentence as proof that bisglycinate beats oxide is quoting a sentence that does not mention bisglycinate. What it supports is that solubility drives absorption and that oxide and sulfate are the poor performers.

The second is Schuette, Lashner and Janghorbani, JPEN 1994;18(5):430–435, a double-blind randomised crossover comparing magnesium diglycinate with magnesium oxide. Three clauses are mandatory whenever it is used and every one of them shrinks the headline. The population was patients with ileal resection, not healthy people who train. The much-quoted doubling applies only to the most malabsorptive subgroup. And overall, the two forms did not differ.

Which leaves the honest sentence, and it is smaller than the one on most labels. The case for bisglycinate is tolerability and the fact that oxide is the documented laggard. It is not an absorption multiple. On the naming: bisglycinate and glycinate are the same chelate and labels use either word — that one is settled in bisglycinate versus glycinate, and the oxide comparison in glycinate versus oxide.

Does magnesium bisglycinate absorb better than other forms?

Magnesium bisglycinate did not absorb better on the newest head-to-head. Pajuelo and colleagues, Nutrients 2024;16(24):4367, n=40, measured plasma magnesium at 0, 1, 4 and 6 hours after four forms. Oxide raised it at 1 hour and citrate at 4 hours, and no significant increase was observed after bisglycinate — the form TARE sells. Two caveats are mandatory: the trial was funded by a company selling a competing ingredient, and a six-hour plasma curve is not magnesium status. We are publishing it anyway.

The design first, because it was a careful one. Double-blind, randomised, crossover. A seven-day low-magnesium run-in. An eight-hour fast before dosing. Capillary blood drawn at baseline and at 1, 4 and 6 hours. Forty healthy women and men. Four comparators: a microencapsulated magnesium, magnesium oxide, magnesium citrate and magnesium bisglycinate.

The result, stated the way the paper states it: plasma magnesium rose significantly at every timepoint after the microencapsulated product, at 1 hour after oxide and at 4 hours after citrate — and no significant increase in magnesium levels was observed upon intake of bisglycinate.

Now the three limits, in the order they matter.

1. The trial was funded by the company that sells the winning ingredient. Every comparator in it competes with the sponsor's product. That cuts against the sponsor's own headline more than it cuts against bisglycinate — but it also means this particular null was produced by a party with an interest in producing it, and pretending otherwise would be its own kind of dishonesty.
2. A six-hour plasma curve is not magnesium status. Serum and plasma hold under 1% of the body's magnesium and are tightly controlled by the body. An acute plasma curve after a single dose is a different question from whether a form works over weeks, and nobody should read this trial as having answered the second one.
3. Single doses, healthy adults, capillary sampling. One dose, one day, blood from a finger.

So why print it. Because we sell magnesium bisglycinate, and this is a published head-to-head in which bisglycinate was the one form that did not significantly raise plasma magnesium. Quoting the 1994 trial while omitting this one is the exact selective citation this Journal exists to refuse. It tightens our position rather than breaking it: the case for this form is tolerability, not an absorption multiple, and that was already the honest case before 2024.

One more entry belongs beside it, because it used our form specifically. Dall and colleagues, Nutrition Research 2023;110:33–43, gave 360 mg a day of magnesium glycinate with 1,000 IU of vitamin D for twelve weeks to 78 completers. Serum 25-hydroxyvitamin D rose against placebo; the bone-turnover marker measured did not differ between groups. It is a combination design, so the magnesium half cannot be isolated. The honest summary of it is the flat one: in the trials that used our form, effects on the markers they measured have been small or absent.

What is the 350 mg upper limit and how much headroom does Night Work leave?

The tolerable upper intake level for supplemental magnesium is 350 mg a day for everyone aged 9 and over, and it counts supplements and medicines only — food and drink are not counted against it. Night Work supplies 275 mg of elemental magnesium in three capsules, which leaves 75 mg. A multivitamin or a greens powder can spend that headroom without announcing it, so add up the elemental milligrams on every panel you take.

This is the most misused number in the category, in both directions, so here it is with the Office of Dietary Supplements' own explanation attached: the RDAs include magnesium from all sources — food, beverages, dietary supplements and medications. The ULs only include magnesium from dietary supplements and medications.

Which is why the upper limit looks lower than the requirement and is not a contradiction. Your spinach does not count against the 350. Your capsules do.

Seventy-five milligrams is not much room, and here is the part that is rarely published anywhere: a multivitamin, a greens blend or an antacid can occupy all of it without the front of the label saying the word magnesium. Magnesium is a routine inclusion in all three. The only way to know is the Supplement Facts panel, which is where the number is legally required to appear.

And it has to be the elemental number you add up. The Office of Dietary Supplements is explicit that the panel declares the amount of elemental magnesium in the product, not the weight of the entire magnesium-containing compound. On our own bottle that is the difference between 275 mg and 2,500 mg: the second figure is the weight of the compound, and adding it to anything would be an arithmetic error of nearly tenfold. The long version is elemental magnesium, and how to read a label.

So the instruction is one line. Add the elemental milligrams from every supplement and medicine you take, and compare the total with 350 — not with 275. What happens above that line, and how far above it matters, is covered in can you take too much magnesium; the panel-reading habit it depends on is in how to read a supplement label.

Can you take magnesium every day?

Daily is what the arithmetic is built for. The RDA is 400 mg for men 19 to 30, 420 mg for men 31 and over, and 310 to 320 mg for women, counted across food, drink, supplements and medicines together. The number to watch is not the serving on its own; it is the daily supplemental total against 350 mg.

For context on where a diet usually lands: analysis of national survey data puts average intake from food alone at 268 mg a day for American men who do not supplement, against a requirement of 400 to 420 mg. And 48% of Americans of all ages take in less magnesium from food and beverages than their respective estimated average requirements.

That 48% is quoted everywhere and almost always wrongly, so the correction belongs here. It is an intake figure, not a diagnosis. It describes how much magnesium people eat relative to an estimated requirement. It is not a blood-test finding, it is not a rate of anything clinical, and no version of that sentence appears on this page or on our label.

Does magnesium help training performance?

Magnesium is not a performance supplement, and the newest trial points the other way. Nutrients 2025;17(5):915, a double-blind crossover in 15 people who exercise regularly, gave magnesium chloride 300 mg twice a day for nine days: VO2max fell from 44.4 to 41.3 mL/kg/min (p=0.005) and mean 30-second sprint power fell from 439 to 415 W (p=0.03). The authors recommend that regular exercisers without low blood magnesium should not supplement for this purpose. Fifteen people, nine days, and a different salt from ours.

Bomar and colleagues ran a two-period crossover with a three-week washout, with muscle biopsies and stool sampling. Circulating ionised magnesium rose (p<0.03), so the supplement was reaching the blood. The 10 km time trial was unchanged (p=0.89). Skeletal-muscle mitochondrial respiration with fatty acids at complex II fell (p=0.04), and gut microbiota diversity was unaffected.

The authors' own recommendation, in substance: regular exercisers free from low blood magnesium should not supplement their diet with magnesium. Their stated hypothesis had been the opposite, which makes this a hypothesis-contradicting result rather than a fishing expedition. And it was funded by New Capstone, Inc., which makes an unfavourable result more credible rather than less.

Four things stop it being bigger than it is, and they are printed here rather than left out: n=15. Nine days. Magnesium chloride, not bisglycinate. And people whose blood magnesium was not low. It is not a study of our product and it should not be read as one.

What it does do is settle the claim we are not going to make. A 2017 review supports the defensible statement that magnesium requirements rise as physical activity rises — training raises the bar you have to clear. It does not support, and this page will never print, the statement that magnesium improves performance. This is the trial that is why.

Does magnesium prevent cramps?

Two designs say no. The 2020 Cochrane review concluded it is unlikely that magnesium provides clinically meaningful cramp prophylaxis at any of the dosages tested. A 2026 prospective analysis of a Swiss population cohort found magnesium users had a higher incidence of night cramps, not lower; the likeliest explanation for that direction is reverse causation, and the usable finding is the failure to prevent.

Garrison and colleagues, Cochrane Database of Systematic Reviews 2020;9:CD009402, pooled data including 322 older adults with idiopathic rest cramps and concluded that meaningful cramp prophylaxis is unlikely at any of the dosages used. For pregnancy-associated rest cramps the literature is conflicting.

Then Stadie, Heinzer and Marques-Vidal, European Journal of Nutrition 2026;65(2):60 — the CoLaus|PsyColaus cohort across three follow-up waves, 3,887 then 1,916 then 1,561 participants. Magnesium users had a higher likelihood of night cramps, and prospectively, baseline users had a higher incidence of them. The authors' conclusion is that magnesium supplementation did not prevent night cramps.

The qualifier on that second one is the most important sentence in this section. It is observational, and the obvious explanation for supplement users cramping more is that people take magnesium because they cramp. The paper cannot separate the two, so it is not evidence that magnesium causes cramps and we are not going to present it as such. Supplement use was self-reported with no dose or form recorded, so it says nothing about bisglycinate specifically. What it can carry is the null: it did not prevent them.

Two different designs, a randomised-trial synthesis and a population cohort, arriving at the same place. If cramps are the reason you are considering this, we would rather you knew before you paid.

Can a blood test tell you whether you need magnesium?

A serum magnesium test tells you very little. The NIH Office of Dietary Supplements states that no current data on magnesium status in the United States are available, that NHANES has not measured serum magnesium in its participants since 1974, and that magnesium is not evaluated during routine electrolyte testing in hospitals and clinics. Serum holds under 1% of the body’s magnesium and is tightly controlled.

Read those two facts together, because between them they reframe the whole category. Nobody is checking, and the check would not tell you much anyway. A tightly regulated compartment holding under one percent of the total is a poor window onto the other ninety-nine.

It is also the reason the absorption trial above carries the caveat it does. A six-hour plasma curve is a measurement of the compartment the body works hardest to keep constant.

Which leads to the question underneath all of this: how would you know whether you need it at all? The honest answer is that most people asking cannot find out from a test, and the intake statistics above are about diets rather than about you. We are not going to print the checklist of vague symptoms that most magnesium pages run at this point. That list is not diagnostic, it is not permitted, and its function is to make a reader recognise themselves in it.

Does magnesium interact with medication?

The medicine question has one honest answer and it is not a study. Ask a pharmacist — it depends on the specific medicine, and they can check it in under a minute. One checkable thing does belong here: magnesium is a primary ingredient in some laxatives and antacids, so a person can already be taking magnesium without counting it against the 350 mg ceiling.

That second point is the only interaction advice on this page that is arithmetic rather than pharmacology, and it is the one most likely to apply to you. If there is an antacid or a laxative in the cupboard, read its panel before you add the 275.

On taking magnesium alongside zinc or calcium: we hold no trial on it, so there is nothing to report. Not a null, not a caution, nothing — and inventing a mechanism to fill the gap would be exactly what this Journal exists not to do. Same destination as the medicine question: a pharmacist.

Who should ask a doctor first

Four groups, and the answer for all four is the same one.

• Anyone with a kidney condition. Nothing on this page transfers, and the clearance of an oral mineral load is precisely the thing a kidney condition changes.
• Anyone pregnant or breastfeeding. Nothing in our citation banks addresses it. Silence is the honest answer.
• Anyone taking prescription medicine. A pharmacist, before the first capsule.
• Anyone under 18. TARE products are dietary supplements for adults 18 and over.

There is no study on this page that would let us say more than ask a clinician, and a page that says more is inventing it.

The warning printed on our own label

The Night Work label carries a California Proposition 65 warning. Its words, in full, are these:

WARNING: Reproductive Harm — www.P65Warnings.ca.gov

Three things about it, and each one is the kind of detail a brand normally leaves for the box to deliver.

• It is the reproductive-harm warning only. The word Cancer is not on the label, and it is not going to appear on any TARE surface, because adding it would be inventing a warning the manufacturer did not print.
• The label names no chemical, and neither does any document in our hands. The legacy short form is not required to name one. So we reproduce the label's words and add nothing to them, and we are not going to guess which listed chemical it is — a guess would be worse than the gap. Closing it with the manufacturer is an open item on our side, and this paragraph changes on the day it closes.
• You see it before you buy, not after. The same warning appears on the Night Work product page ahead of the purchase, which is the method California's rules require for an internet sale — the one on the bottle does not replace it.

What is in the bottle, and what our certificate does not cover

Night Work is magnesium glycinate in a capsule. Three capsules supply 275 mg of elemental magnesium, 65% of the Daily Value, from 2,500 mg of magnesium glycinate. Ninety capsules in the bottle, which is 30 servings — thirty, not ninety, because the serving is three.

Now the sentence that governs every magnesium figure on this site. The 275 mg is not a measured number. It rests on the manufacturer's written confirmation of 27 August 2026 and on nothing else. No certificate in our hands reports an elemental magnesium result for this product, and we never describe that figure as measured.

What the certificate we hold does cover is one axis out of four. It was issued by an independent laboratory that had nothing to do with making the product — Ethos Analytics, Phoenix, Arizona — completed on 9 March 2026, with Vox Nutrition as the customer of record rather than TARE. The sample photographed on it is a sealed poly bag of magnesium glycinate raw-material powder, lot MGL260212. Not a TARE bottle. Not a TARE fill lot.

That last row is worth a sentence of its own because it is the commonest way a certificate gets over-read. The heavy-metal table on our document has populated columns for limit of quantification, limit of detection and the acceptance limit — and the Result column reads Not Tested for arsenic, cadmium, lead and mercury, with the pass-or-fail column left as a dash. Those first three columns are the laboratory's method parameters and the regulatory limit. None of them is a measurement, and a page that presents them as one is presenting a specification as a result.

We publish that document as 1 of 4. Row by row, with the untested axes marked, on Testing & Certification and on the Night Work lot page. What a certificate can and cannot prove in general is unpacked in what a certificate of analysis proves.

More in this cluster: bisglycinate versus glycinate, glycinate versus oxide, threonate versus glycinate, can you take too much magnesium, and how to read an elemental magnesium figure. Or read the documents themselves on Testing & Certification.