Magnesium Oxide Powder USP — Heavy Grade Dietary Supplement
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Dietary supplement · Magnesium oxide powder, USP/FCC grade · At least 520 mg magnesium per gram
About Magnesium Oxide Powder
Greenway Biotech Magnesium Oxide Powder is heavy-grade magnesium oxide (MgO) that meets the USP and FCC monographs, sold as a plain white powder with nothing else added: no flavors, sweeteners, fillers, or flow agents. It is a dietary supplement taken by mouth, a quarter of a level teaspoon stirred into water or juice or mixed into food, and it carries more magnesium per gram than any other form Greenway sells: at least 520 mg of elemental magnesium per gram of powder, about 560 mg in the current lot.
Magnesium is a cofactor in more than 300 enzyme systems and supports normal muscle and nerve function, energy production, and the structural development of bone.* Magnesium oxide is the concentrated, economical form, and that concentration is also its limitation: the serving is tiny and must be measured level, and the NIH Office of Dietary Supplements reports that small studies have found magnesium oxide to be less completely absorbed than more soluble forms such as citrate and chloride. If you want the most magnesium per gram in the smallest serving, this is it; if absorption per milligram is your first concern, Magnesium Citrate Powder or Magnesium Chloride USP is the better fit.
- ≥520 mg / g Elemental magnesium per gram of powder as sold, guaranteed at the specification floor; the current lot supplies about 560 mg
- ¼ level tsp The Supplement Facts serving, about 0.4 g: at least 200 mg of magnesium (48% Daily Value), one serving a day
- 1, 2 & 5 lb bags More than 1,100 servings in a 1 lb bag; see Choosing a size
Product facts & composition
| Specification | Detail |
|---|---|
| Ingredient | Magnesium oxide (MgO), heavy grade, CAS 1309-48-4. No other ingredients. |
| Grade | Meets the USP and FCC monographs for magnesium oxide and the E 530 food-additive specification, tested to those monographs on the certificate of analysis for the current lot. “Heavy” is the denser of the two pharmacopeial bulk grades, heavy and light. |
| Assay | 99.62% magnesium oxide on the ignited basis (specification 96.0–100.5%). Pure magnesium oxide is 60.3% magnesium by weight (24.305 ÷ 40.304). |
| Elemental magnesium | 59.02% on the ignited basis for the current lot (specification 57.9–60.6%). As sold, after the lot’s 4.45% loss on ignition, about 56.4%; the guaranteed floor as sold, at the specification minimum and the maximum 10% loss on ignition, is 52%. |
| Magnesium per serving | A quarter of a level teaspoon (about 0.4 g) supplies at least 200 mg of magnesium (48% of the 420 mg Daily Value); about 225 mg at the current lot’s analysis. |
| Form and appearance | Very bulky, fine white powder; median particle size below 8 µm (laser diffraction). Loose bulk density 0.33 g/mL, tapped density 0.56 g/mL (current lot). |
| Solubility | Practically insoluble in water and insoluble in alcohol; soluble in dilute acids (USP/FCC solubility test, current lot). In a glass it forms a suspension, not a solution. A water suspension tests alkaline. |
| Other specifications (current lot) | Loss on ignition 4.45% (limit 10.0%); acid-insoluble substances 0.080% (limit 0.1%); calcium below 1.1% (limit 1.1%); iron below 0.05% (limit 0.05%); calcium oxide below 1.5% (limit 1.5%); free alkali and soluble salts within the USP/FCC limits. |
| Heavy metals (current lot) | Lead below 0.25 ppm (limit 0.25); arsenic below 2 ppm (limit 2); cadmium below 1 ppm (limit 1); mercury below 0.1 ppm (limit 0.1). |
| Microbiological (current lot) | Total aerobic count 130 cfu/g (limit 1,000); yeast and mold 10 cfu/g (limit 100); E. coli, Pseudomonas aeruginosa, Staphylococcus aureus, Salmonella, Listeria, and Enterobacteriaceae absent. |
| Shelf life | The current lot, manufactured August 2025, carries an expiry of July 2030 when stored tightly closed and dry. |
| Package sizes | 1 lb (454 g), 2 lb (907 g), and 5 lb (2.27 kg) bags |
| Packaged by | Greenway Biotech, Inc., 17861 Road 24, Madera, California 93638 |
Percentages are by weight of product as sold unless the row says otherwise. A 1 lb bag contains at least 236 g of elemental magnesium (about 256 g at the current lot’s analysis). Every serving on this page is stated as product weight, with the magnesium it delivers shown beside it, and the figures marked “current lot” come from the certificate of analysis for the lot on hand; they are lot-specific results, not a standing guarantee.
Best uses & benefits
Choose this product when you want the most concentrated magnesium powder, in a serving small enough to stir into a glass or a spoonful of food. Every statement below about magnesium is about the nutrient, drawn from the NIH Office of Dietary Supplements, and not a trial of this finished product.
Meeting your daily magnesium needs in the smallest serving
The Recommended Dietary Allowance is 400–420 mg per day for adult men and 310–320 mg for adult women, and national dietary surveys consistently find that many Americans take in less than recommended amounts. A quarter of a level teaspoon supplies at least 200 mg of magnesium, 48% of the Daily Value, to add to the magnesium in your food.*
Supporting muscle and nerve function and energy production
Magnesium is a cofactor in more than 300 enzyme systems, including those involved in protein synthesis and muscle and nerve function, and it is required for energy production.*
Supporting bone structure
About half to 60% of the body’s magnesium is held in bone, and magnesium contributes to the structural development of bone. Green leafy vegetables, legumes, nuts, seeds, and whole grains are good food sources; a supplement is one way to add to that intake.*
The most magnesium per gram, at USP/FCC grade
Pure magnesium oxide is 60% magnesium by weight, against about 12% for magnesium citrate and magnesium chloride hexahydrate, so a bag of this powder holds four to five times the magnesium of the same bag of either. It is tested to the USP and FCC monographs, with heavy metals and microbial counts on the certificate of analysis for the current lot. The trade-off is absorption, explained under How it works.
Where it is a poor fit
- If absorption per milligram is your first concern. The NIH states that forms of magnesium that dissolve well in liquid are more completely absorbed than less soluble forms, and that small studies have found magnesium oxide less bioavailable than citrate, chloride, lactate, and aspartate. Magnesium Citrate Powder is the soluble alternative.
- As an antacid or laxative. This powder is a dietary supplement; it is not labeled for either use. Do not take more than the serving on the panel. See the FAQ on antacids and laxatives.
- If you have kidney disease. The NIH notes that the risk of magnesium toxicity rises with impaired kidney function because the body’s ability to remove excess magnesium is reduced. Do not take this or any magnesium supplement without your physician’s direction.
- If you cannot measure a quarter teaspoon level. Because the powder is so concentrated, a heaped or packed quarter teaspoon can nearly double the magnesium. If you would rather measure a full teaspoon, Magnesium Citrate Powder is served by the level teaspoon.
- For a bath, foot soak, or topical routine. This product is labeled for oral use and does not dissolve in bath water. For soaking, Epsom Salt (magnesium sulfate) is labeled for external use, and Magnesium Chloride USP covers both a drink and a soak.
- As a fertilizer or soil amendment. It is not labeled or registered as a plant nutrient or liming material. Greenway sells magnesium for plants separately.
*These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease. The asterisk marks each statement this disclaimer covers, wherever it appears on this page.
Serving size & directions
The directions below reflect the Supplement Facts panel for this product. The serving is a quarter of a level US teaspoon, about 0.4 g of powder. This powder is light and very fine, so the way the spoon is filled matters more than it does for most supplements: fill the ¼ teaspoon loosely, do not press or tap it, and level it with the back of a knife. A packed quarter teaspoon can hold up to about 0.7 g and nearly twice the magnesium. If you own a scale that reads to 0.1 g, weighing 0.4 g is the most precise method.
| Direction | Amount | Magnesium supplied | Notes |
|---|---|---|---|
| Serving size | ¼ level teaspoon (about 0.4 g) | At least 200 mg (48% DV); about 225 mg at the current lot’s analysis | Stir into 8 fl oz (240 mL) or more of water or juice and drink right away while it is suspended, or mix into a spoonful of yogurt, applesauce, or a smoothie. Take with a meal. |
| Servings per day | 1 | Under the 350 mg per day Tolerable Upper Intake Level for supplemental magnesium when the spoon is level; a packed quarter teaspoon can exceed it | Do not take a second serving. The 350 mg limit applies to magnesium from supplements and medications, not from food; count any other magnesium-containing supplement or medication you use toward it. |
| First few days, if you are new to magnesium | ⅛ level teaspoon (about 0.2 g) | At least 100 mg; about 110 mg | Greenway’s suggestion, not a panel requirement: half a serving for a few days lets you check tolerance before moving to the full quarter teaspoon. |
| Per 0.1 g of powder (for a provider-set target) | 0.1 g | At least 52 mg; about 56 mg | Use this to work out a smaller serving if your healthcare provider gives you a target in milligrams of magnesium: grams of powder = target mg ÷ 520 (guaranteed) or ÷ 560 (current lot). Amounts this small are best weighed on a 0.1 g scale. |
Who it is for. Adults. Not for children unless a pediatrician directs it; the upper limit for supplemental magnesium is lower for young children. If you are pregnant or nursing, have kidney disease, or take any prescription medication, ask your healthcare provider before use. Specific medication timing from the NIH: take magnesium at least 2 hours before or after an oral bisphosphonate, and take tetracycline or quinolone antibiotics at least 2 hours before, or 4 to 6 hours after, a magnesium supplement. Long-term proton pump inhibitor use and some diuretics change magnesium status; your provider can advise whether a supplement is appropriate and at what amount.
If you exceed the serving. Loose stools or diarrhea are the expected sign of too much supplemental magnesium; the NIH attributes them to the osmotic activity of unabsorbed magnesium salts in the intestine. Reduce the amount or stop. Very large intakes, especially with impaired kidney function, can cause more serious effects; seek medical attention for symptoms beyond digestive upset.
Worked example. Your provider suggests about 150 mg of supplemental magnesium a day. 150 ÷ 560 = 0.27 g of powder at the current lot’s analysis (0.29 g if you use the guaranteed 520 mg per gram), which is between an eighth and a quarter of a level teaspoon. Weigh it if you can, stir it into a glass of water with breakfast, and drink it right away.
How to use Magnesium Oxide Powder
- Check that it suits you. Read the Supplement Facts panel. If you have kidney disease, are pregnant or nursing, or take medication, ask your healthcare provider first, and space it from antibiotics or bisphosphonates as described under Directions.
- Measure a level quarter teaspoon. Fill a ¼ US measuring teaspoon loosely, without pressing or tapping, and level it off with a knife: about 0.4 g (an eighth of a teaspoon for your first few days). Open and close the bag gently; the powder is fine enough to raise dust. Reseal it tightly right away.
- Mix it in. Stir into 8 fl oz (240 mL) or more of water or juice and drink it right away, before the powder settles; it does not dissolve, and a chalky suspension is normal. It also mixes into yogurt, applesauce, or a smoothie.
- Take it with food. One serving a day with a meal, at whatever time of day suits your routine.
- Notice how you tolerate it. Loose stools mean the amount is too high for you: drop back to an eighth of a teaspoon, or switch to a more soluble form. If you take other magnesium-containing products, count them toward the 350 mg daily supplement limit.
Choosing a size
This product has no calculator: the serving is fixed by the Supplement Facts panel, so the only question is how many servings you want on hand, and with magnesium oxide the answer is usually “more than you think.” Servings per bag = bag weight in grams ÷ 0.4. One person taking one serving a day uses about 12 g a month, so even the 1 lb bag is a multi-year supply for one person. The larger bags suit households, practitioners, and formulators.
| Package | Servings | One person, one serving a day | Elemental magnesium in the bag |
|---|---|---|---|
| 1 lb (454 g) | About 1,100 | About 3 years | At least 236 g (about 256 g at the current lot’s analysis) |
| 2 lb (907 g) | About 2,250 | About 6 years, or 3 years for two people | At least 473 g (about 512 g) |
| 5 lb (2.27 kg) | About 5,600 | A household or formulating quantity | At least 1.18 kg (about 1.28 kg) |
Because the powder is so light (about 0.33 g/mL loose), a 1 lb bag is roughly 1.4 liters of powder, larger than the same weight of most supplements. Keep any bag tightly closed, because the safety data sheet describes the powder as hygroscopic and air-sensitive. Select a size from the options at the top of this page; prices, tax, and shipping are shown at checkout.
How magnesium oxide works
The NIH Office of Dietary Supplements describes magnesium as a cofactor in more than 300 enzyme systems that regulate diverse biochemical reactions, including protein synthesis and muscle and nerve function, and as required for energy production, oxidative phosphorylation, and glycolysis; it also contributes to the structural development of bone and plays a role in the active transport of calcium and potassium ions across cell membranes.* An adult body holds roughly 25 g of magnesium, 50–60% of it in bone, and less than 1% in blood serum, which is why a serum test is a poor guide to total body status.
Magnesium oxide is the simplest magnesium compound: one magnesium atom to one oxygen atom, MgO, 60.3% magnesium by weight. The “heavy” grade in this bag is the denser of the two pharmacopeial bulk grades. It is practically insoluble in water, which is why a serving forms a chalky suspension rather than a clear drink, and soluble in dilute acids (the USP and FCC solubility test on the certificate of analysis). Once absorbed, the kidneys regulate how much magnesium the body retains.
That solubility difference is the whole story of oxide versus citrate. The NIH states that forms of magnesium that dissolve well in liquid are more completely absorbed in the gut than less soluble forms, and that small studies have found the aspartate, citrate, lactate, and chloride forms to be absorbed more completely and to be more bioavailable than magnesium oxide and magnesium sulfate. Two of those small studies are listed under Product documents & sources: a 60-day randomized trial (Walker and colleagues, 2003) that found magnesium citrate more bioavailable than magnesium oxide and an amino-acid chelate at 300 mg of magnesium per day, and a single-dose crossover study (Kappeler and colleagues, 2017) that measured higher urinary magnesium excretion after citrate than after oxide. Neither is a trial of this finished product, and neither establishes a fixed multiple; read them as the reason the serving on this page is a quarter teaspoon of a 60% material rather than a smaller amount, and as the reason to choose a soluble form if absorption per milligram matters most to you.
The same solubility is behind the upper limit. Magnesium that is not absorbed stays in the intestine, where the NIH notes its osmotic activity can cause loose stools; that adverse effect is the reason the panel stops at one level quarter teaspoon a day and the spoon must not be packed.
Compare your options
Greenway sells magnesium in several forms for different routes. Match the product to the route it is labeled for; an external-use product is not an oral one, whatever its grade.
| Option | Magnesium content and form | Labeled route | Choose it when | Limitation |
|---|---|---|---|---|
| Magnesium Oxide Powder, this product | At least 52% magnesium as sold (about 56% in the current lot); pure MgO is 60.3% | Oral dietary supplement | You want the most magnesium per gram, in the smallest serving, at USP/FCC grade | Insoluble; less completely absorbed than soluble forms in small studies; the quarter-teaspoon serving must be level and unpacked |
| Magnesium Citrate Powder | At least 11% magnesium as hydrated trimagnesium citrate; about 12% in the current lot | Oral dietary supplement | You want a soluble form in a one-level-teaspoon serving | Dissolves slowly; a fifth of the magnesium per gram |
| Magnesium Chloride USP | About 12% magnesium as magnesium chloride hexahydrate (24.305 ÷ 203.31 = 11.96%) | Oral solution as directed on its page, and bath or DIY magnesium oil | You want one product for both a drink and a soak, or you want the chloride form | Hygroscopic; oral use follows that product’s own label and page |
| Epsom Salt (Magnesium Sulfate) | About 10% magnesium as magnesium sulfate heptahydrate | External use: bath and foot soak; garden use as labeled | You want a soak, not a supplement | Not labeled for oral use |
| Magnesium Oil Spray | Magnesium chloride brine, ready to use | Topical | You want a skin-applied magnesium chloride routine alongside a supplement | A topical product; it is not a substitute for dietary magnesium |
For the oral-versus-topical decision in more depth, read our guide to oral and topical magnesium routes.
Handling, storage & limitations
- Daily limit. Keep supplemental magnesium at or below 350 mg per day for adults unless a healthcare provider directs otherwise, counting every supplement and medication that contains magnesium. Excess causes loose stools first; very high intakes, especially with impaired kidney function, can cause low blood pressure, nausea, muscle weakness, and other serious effects (NIH Office of Dietary Supplements). With this product, a level quarter teaspoon is the serving; a heaped or packed spoon is the most likely way to overshoot.
- Who should ask first. People with kidney disease; anyone pregnant or nursing; anyone taking bisphosphonates, tetracycline or quinolone antibiotics, diuretics, or proton pump inhibitors; and children, who should use it only under a pediatrician’s direction.
- Not a drug. This is a dietary supplement. It is not an antacid or laxative product, it is not labeled for either use, and it is not for external use, bath use, or plant use.
- Handling the dry powder. The safety data sheet for this material classifies the powder as a skin irritant, an eye irritant, and a possible respiratory irritant (as dust), with the signal word Warning, and notes that inhaling or swallowing large quantities of the dust can cause a feverish reaction. Those statements describe handling the bulk powder, not a serving in a glass; the particles are very fine, so open the bag gently, keep your face out of it, avoid raising or breathing dust, keep it out of your eyes, wash your hands after handling it, and sweep up spills without raising dust.
- Storage. Keep the bag tightly sealed in a dry, well-ventilated place away from strong acids and oxidizing agents (SDS). The safety data sheet notes the material is hygroscopic and air-sensitive, which is why the bag must be resealed after every serving. Use by the expiry date printed on the bag. Keep out of reach of children.
- Transport and regulatory. Not regulated as a hazardous material for transport. Not listed under California Proposition 65, and not listed as a carcinogen by IARC, NTP, or OSHA (SDS).
- First aid (from the safety data sheet). Eyes: flush with plenty of water for several minutes; remove contact lenses if easy to do; get medical attention if irritation persists. Skin: wash with soap and plenty of water; remove contaminated clothing. Dust inhaled: move to fresh air; get medical attention if symptoms persist. Swallowed in a large amount: rinse mouth with water; never give anything by mouth to an unconscious person; get medical attention if symptoms occur.
- Poison Control. For poisoning advice in the United States, call Poison Control at 1-800-222-1222, 24 hours a day.
Frequently asked questions
What is magnesium oxide powder, and how much magnesium is in it?
It is magnesium oxide, MgO, the simplest and most concentrated magnesium compound, in the heavy USP/FCC grade, sold as a fine white powder with no other ingredients. Pure magnesium oxide is 60.3% magnesium; this product is guaranteed to supply at least 520 mg of elemental magnesium per gram as sold, and the current lot supplies about 560 mg. The quarter-teaspoon serving of about 0.4 g supplies at least 200 mg (48% of the Daily Value), and a 1 lb bag holds about 1,100 servings.
How much magnesium oxide powder should I take each day?
A quarter of a level teaspoon (about 0.4 g) a day, stirred into 8 fl oz or more of water or juice or mixed into soft food, and taken with a meal, which supplies at least 200 mg of magnesium. The Tolerable Upper Intake Level for magnesium from supplements and medications is 350 mg per day for adults; a level quarter teaspoon stays under it and a packed one can exceed it, so measure loosely and level, do not take a second serving, and count any other magnesium-containing supplement or medication toward the limit. If you are new to magnesium, an eighth of a teaspoon for the first few days lets you check tolerance. Your healthcare provider may set a different target; at 520–560 mg of magnesium per gram, a smaller amount is best weighed.
Why is the serving so small, and how do I measure it accurately?
Because magnesium oxide is about 60% magnesium, five times the concentration of magnesium citrate or magnesium chloride, its serving is a quarter teaspoon where theirs is a full one. Use a ¼ US measuring teaspoon, fill it loosely without pressing or tapping, and level it with the back of a knife. This powder is light and compressible: loosely filled, a quarter teaspoon weighs about 0.4 g, but packed down it can hold about 0.7 g and nearly twice the magnesium, so the loose, level fill is the one the panel is based on. A kitchen scale that reads to 0.1 g removes the variable entirely.
Is this an antacid or a laxative?
No. Magnesium oxide is listed as an antacid active ingredient in the FDA over-the-counter antacid monograph, and magnesium hydroxide is used in over-the-counter laxatives; those are drugs, labeled and dosed for their purposes. This powder is a dietary supplement, labeled for a quarter-teaspoon daily serving of about 200 mg of magnesium, and it is not labeled or intended for antacid or laxative use. If you need an antacid or a laxative, use a product labeled as one and follow its directions.
Magnesium oxide or magnesium citrate: which should I choose?
Oxide for concentration and economy, citrate for absorption. The NIH Office of Dietary Supplements reports that small studies have found citrate, chloride, lactate, and aspartate forms to be absorbed more completely than magnesium oxide, while oxide carries about five times the magnesium per gram. If you want the smallest serving and the most magnesium per bag, choose this product and measure it level; if you want a soluble form that makes a clear drink and a comfortable one-teaspoon serving, choose Magnesium Citrate Powder. Whichever you choose, take one, not both, unless your provider has set a combined target.
Will it dissolve?
No. Magnesium oxide is practically insoluble in water (the USP and FCC solubility test on the certificate of analysis confirms it), so a serving makes a chalky suspension that settles if left standing. Stir it and drink it right away, or mix it into yogurt, applesauce, or a smoothie. It is soluble in dilute acids and alkaline in water, so it will neutralize some of the acid in a tart juice; plain water is the simplest carrier.
Can I take magnesium oxide with my medications?
Ask your healthcare provider or pharmacist, and follow the timing the NIH gives for the known interactions: take magnesium at least 2 hours before or after an oral bisphosphonate, and take tetracycline or quinolone antibiotics at least 2 hours before, or 4 to 6 hours after, a magnesium supplement. Loop and thiazide diuretics and long-term proton pump inhibitor use affect magnesium status, so your provider may want to check your level before you supplement. If you have kidney disease, do not take magnesium supplements without medical direction, since impaired kidneys clear the excess poorly.
Who should not take this product?
It is labeled for adults. Children should use it only under a pediatrician’s direction; the upper limit for supplemental magnesium is lower for young children. People with kidney disease should not use it without their physician’s direction. If you are pregnant or nursing, ask your provider first; the Recommended Dietary Allowance is somewhat higher in pregnancy, and the serving on this page may or may not fit your plan. Stop and consult a provider if you have persistent digestive upset.
Is it USP grade, and is it tested for heavy metals?
Yes to both. The certificate of analysis for the current lot reports that the material complies with the USP and FCC monographs for magnesium oxide, with an assay of 99.62% on the ignited basis, and reports lead below 0.25 ppm, arsenic below 2 ppm, cadmium below 1 ppm, and mercury below 0.1 ppm, each at or under its limit, with total aerobic count 130 cfu/g, yeast and mold 10 cfu/g, and E. coli, Pseudomonas aeruginosa, Staphylococcus aureus, Salmonella, Listeria, and Enterobacteriaceae absent. Those are results for the lot on hand. Ask us for the certificate for the lot you receive.
Can I use it in the bath, in the garden, or for anything else?
No. It is labeled for oral use as a dietary supplement only. It does not dissolve in bath water, so it is useless as a soak; for a bath or foot soak, use Epsom Salt or Magnesium Chloride USP, which are labeled for that. For plants, use a magnesium product that is labeled and registered as a fertilizer or liming material. This page gives directions for one use, the labeled one.
Related guides & articles
- Oral vs. Transdermal Magnesium: Which Method Is Right for You?: how oral magnesium is absorbed and dosed, what the evidence for skin-applied magnesium does and does not show, and how the two routes fit together in one routine.
Articles give background. For this product, use the Supplement Facts panel and the directions on this page.
Product documents & sources
- Supplement Facts label: available on request; the serving size, magnesium per serving, and Daily Value on this page are taken from it.
- Certificate of analysis for the current lot: available on request; the USP/FCC monograph tests, assay, magnesium content, heavy-metal, microbiological, and physical results quoted on this page.
- Safety Data Sheet: available on request; composition, hazard classification of the dry powder, handling, storage, and first aid.
Where the rates and statements on this page come from
The serving and its magnesium content come from this product’s Supplement Facts panel and certificate of analysis; the statements about magnesium’s roles, intake recommendations, upper limit, absorption, interactions, and precautions come from the public sources below. They are listed for shoppers, practitioners, and reviewers who want to check them; none of them evaluates or endorses this product.
- National Institutes of Health, Office of Dietary Supplements, Magnesium Fact Sheet for Health Professionals: magnesium’s physiological roles, body distribution, the Recommended Dietary Allowances, the 420 mg Daily Value, the 350 mg Tolerable Upper Intake Level for supplemental magnesium and the osmotic basis of its laxative effect, the absorption of soluble forms versus magnesium oxide, the bisphosphonate, antibiotic, diuretic, and proton pump inhibitor interactions, and the kidney-function caution.
- U.S. Food and Drug Administration, Daily Value on the Nutrition and Supplement Facts Labels: the 420 mg Daily Value used for the percent Daily Value on this page.
- Walker AF, Marakis G, Christie S, Byng M. Mg citrate found more bioavailable than other Mg preparations in a randomised, double-blind study. Magnesium Research 2003;16(3):183–191: the 60-day comparison of citrate, oxide, and amino-acid chelate cited under How it works.
- Kappeler D, Heimbeck I, Herpich C, et al. Higher bioavailability of magnesium citrate as compared to magnesium oxide shown by evaluation of urinary excretion and serum levels after single-dose administration in a randomized cross-over study. BMC Nutrition 2017;3:7: the single-dose citrate-versus-oxide comparison cited under How it works.
- 21 CFR 101.93, Certain types of statements for dietary supplements: the wording and placement of the disclaimer that accompanies the structure/function statements on this page.
- 21 CFR Part 331, Antacid products for over-the-counter human use: the monograph that lists magnesium oxide among antacid active ingredients, cited to explain why antacid and laxative products are drugs and this supplement is not one.
Statements and sources reviewed September 15, 2026.
Help choosing & next step
Not sure whether oxide or citrate is the right form for you, or how a serving fits a target your provider gave you in milligrams? Email questions@greenwaybiotech.com or call (562) 351-5168, Monday to Friday, 7 AM to 5 PM Pacific. We can explain the product and its documents; we cannot give medical advice, so bring questions about your own health or medications to your healthcare provider.
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