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Magnesium Oxide

Magnesium oxide is a magnesium-based medicine taken by mouth as a tablet to relieve acid indigestion and upset stomach, and also used as a daily magnesium dietary supplement.

Brand names Mag-OxMaoxUro-MagMag-Ox 400Phillips' Cramp-free +2 more
Drug class Calculi Dissolution Agent
OTC Form 1
Dr. Brian Staiger, PharmD, BCPS
Reviewed by Last reviewed Jul 10, 2026 Content updated Oct 2, 2026
🧬 Where this information comes from Click to expand

The clinical label records used on this page are FDA-filed Structured Product Labeling (SPL) retrieved through openFDA. We identified 22 clinical label sets within the page’s selected clinical scope after exact ingredient or ingredient-combination matching and applicable route/form matching. Forms, routes, brands, labelers, strengths, and NDC product-record counts are built separately from matching FDA National Drug Code Directory records. The linked DailyMed document is a representative official source for verification, not the page’s only clinical source. View the linked label on DailyMed →

How we combine label and product data →
✓No current FDA shortage listed · checked Oct 4, 2026
Magnesium Oxide at a glance The quick version — the full detail is in the Patient Information Guide below.
Dr. Brian Staiger, PharmD, BCPS
The Pharmacist’s Take By · Clinical pharmacist · Written

Magnesium oxide is an inexpensive over-the-counter standby that neutralizes stomach acid to relieve acid indigestion and upset stomach. Some products are also labeled as a daily magnesium supplement, and many companies make it. Most people tolerate it well, and the side effect they notice is a laxative effect, meaning looser or more frequent stools. Check with a doctor first if you have kidney disease (healthy kidneys are what clear extra magnesium), take prescription drugs, or are pregnant or breastfeeding. Never use the maximum dose longer than two weeks without a doctor supervising.

Clinical pearls

  • Needing more than two tablets in 24 hours is your signal to call a doctor, not to take more.
  • Check which product you bought, since the antacid and supplement versions give different directions for how often to take them.
  • The dietary supplement version is best taken with food, as its label prefers.
  • Antacids can interfere with some prescription drugs, so mention magnesium oxide whenever a new prescription is started.
How we write & review this content — our editorial policy →
How you get itOver the counter
Comes asTablet
Earliest FDA record1982
Companies listing it with the FDA19
FDA label last updatedOct 25, 2018
FDA’s strongest warning (boxed)None on the label

Patient information guide — a plain-language walkthrough of Magnesium Oxide, written from its FDA label.

What Magnesium Oxide is used for

▾

Magnesium oxide tablets are used for these purposes, depending on the product:

  • Antacid tablets: relieve acid indigestion and upset stomach.
  • Magnesium Oxide 400mg tablets: relieve acid indigestion and upset stomach, and serve as a magnesium supplement.
  • magnesium oxide tablets (dietary supplement): suggested for adults as a daily supplement.

Magnesium Oxide dosage

▾

Magnesium oxide is taken by mouth as a tablet. Each product has its own directions, so follow the one on your label or from your prescriber.

  • Antacid tablets: 1 tablet twice a day, or as directed by a physician.
  • Magnesium Oxide 400mg tablets: antacid use is 1 tablet twice a day; supplement use is 1 to 2 tablets daily.
  • magnesium oxide dietary supplement tablets: 1 tablet daily for adults, preferably with food.

Dosing details from the FDA-approved label

From the Magnesium Oxide prescribing information (“Dosage and Administration”). Doses are set by your prescriber for your product, condition, kidney function and age — never change a dose on your own.

  • Antacid
    • Take 1 tablet twice a day or as directed by a physician
  • Magnesium Supplement
    • Take 1 to 2 tablets daily or as directed by a physician
Read the label’s full dosing text

Dosage and Administration Antacid Directions Take 1 Tablet twice a day or as directed by a physicain. Magnesium Supplement Directions: Take 1 to 2 Tablets daily or as directed by a physician.

Read the full Dosage and Administration section on DailyMed →

Magnesium Oxide side effects

▾

Common side effects

  • Laxative effect (loose or more frequent stools)

When to get medical help

  • Call your doctor if you need more than 2 tablets in 24 hours.
  • Check with a doctor if you need the maximum dose for more than two weeks.
  • Talk to a doctor or pharmacist if you take prescription drugs and notice anything unusual after starting this.

The main effect named on the label is a laxative effect.

  • Loose or more frequent stools

Talk to a doctor if you need more than the labeled amount or use it for more than two weeks.

Magnesium Oxide warnings and precautions

▾
  • Do not take more than 2 tablets in 24 hours.
  • Do not use the maximum dose for more than two weeks unless a doctor advises and supervises you.
  • It may have a laxative effect.
  • Keep out of reach of children.

Magnesium Oxide interactions

▾

Antacids like magnesium oxide may interact with certain prescription drugs.

  • Prescription drugs: ask a doctor or pharmacist before use, since interactions are possible.

Not a complete list. The label covers the interactions the manufacturer studied or reported, and our own interaction database does not cover every medicine either. Bring your full medication list, including vitamins and herbal products, to your pharmacist.

Check Magnesium Oxide against a supplement or herb →

Before taking Magnesium Oxide

▾
  • Kidney disease: ask a doctor before use.
  • Prescription drugs: ask a doctor or pharmacist before use.
  • Pregnancy or breastfeeding: ask a health professional before use.
  • Children: keep this product out of their reach.

How to store Magnesium Oxide

▾

Store at controlled room temperature 15° to 30°C (59° to 86°F).

Written from the FDA-approved label with AI and reviewed by our pharmacy team. How we use AI →

Magnesium Oxide: pharmacist answers to common questions

Quick, plain-English answers to the questions patients ask most about Magnesium Oxide — the kind of thing our pharmacy team would talk through with you at the counter.

What is magnesium oxide for?

▾
It's used to relieve acid indigestion and upset stomach. Some products, like Magnesium Oxide 400mg, are also used as a magnesium supplement. Check which use your product is labeled for.

How often should I take it?

▾
For antacid use, the labels say 1 tablet twice a day or as directed by your doctor. For supplement use, the directions vary by product, from 1 tablet daily to 1 to 2 tablets daily. Follow your own label and your prescriber.

Should I take it with food?

▾
The dietary supplement tablet suggests taking it preferably with food. The other labels don't give a food instruction, so follow what's on your package or what your prescriber tells you.

What side effects might I notice?

▾
The main one is a laxative effect, meaning looser or more frequent stools. If that bothers you or you're using more than the label allows, check in with your doctor or pharmacist.

Can I take it with my other medicines?

▾
Ask first. Antacids can interact with certain prescription drugs. Bring your medication list to me or your doctor before you start.

Who should check with a doctor before using it?

▾
Talk to a doctor first if you have kidney disease, take prescription drugs, or are pregnant or breastfeeding. Also, don't take more than 2 tablets in 24 hours or use the maximum dose longer than two weeks without medical supervision.

Is Magnesium Oxide available over the counter?

▾
Yes. The Magnesium Oxide products listed with the FDA are sold over the counter, without a prescription (the tablet form). Follow the package directions. Your pharmacist can tell you which product is right for you.

When was Magnesium Oxide first available?

▾
The earliest FDA record we hold for Magnesium Oxide is from 1982: its first approval in Drugs@FDA or its earliest product listing in the NDC Directory, whichever is older. Many older medicines were in use before their first formal FDA approval, so this is the earliest date on record, not necessarily when Magnesium Oxide was first used.

Who makes Magnesium Oxide?

▾
19 companies list Magnesium Oxide products in the FDA's NDC Directory, including Bryant Ranch Prepack, Westminster Pharmaceuticals, LLC, Dead Sea Periclase. That count includes repackagers and distributors as well as manufacturers, so fewer companies actually make it; the label on your bottle names the one that supplied yours.

Answers drafted from the FDA-approved label with AI and reviewed by our pharmacy team. How we use AI →

More about Magnesium Oxide on HelloPharmacist

🌿Drug & Supplement CheckerMagnesium Oxide vs. vitamins & herbs 💬Ask a PharmacistFree answer, usually < 24h 🔎NDC & pricing lookupFind Magnesium Oxide NDCs & costs 🅰️Browse Drugs A–ZLook up any medication
Detailed data & references for Magnesium Oxide Forms & strengths, pricing, billing codes, manufacturers, safety reports and sourcing — the data behind the page. Most people can stop here. Each section below opens on a tap.

Magnesium Oxide forms and strengths (how it comes)

Magnesium Oxide is available in 1 form. Different forms and brands can have different approved uses, doses, schedules, and directions. Follow the instructions for your exact product, and do not switch forms without guidance from your prescriber or pharmacist.

Tablet

By mouth
Brands Antacid
How this form is used
What it may be used for
  • Antacid tablets relieve acid indigestion and upset stomach.
  • Magnesium Oxide 400mg tablets relieve acid indigestion and upset stomach.
  • Magnesium Oxide 400mg tablets are also directed for use as a magnesium supplement.
  • magnesium oxide tablets are suggested as a dietary supplement for adults.
Important instructions
  • Antacid tablets: take 1 tablet twice a day or as directed by a physician.
  • Magnesium Oxide 400mg tablets: for antacid use, take 1 tablet twice a day; for supplement use, take 1 to 2 tablets daily, or as directed by a physician.
  • magnesium oxide tablets: as a dietary supplement, adults take 1 tablet daily, preferably with food, or as directed by a healthcare practitioner.
Available strengths 5 strengths
241.3 mg/1000 mg 253 mg 400 mg 400 mg/400 mg 420 mg
50 FDA-listed product records ⓘ

Magnesium Oxide on the U.S. market: products, makers and brands

How Magnesium Oxide appears in the FDA’s National Drug Code Directory — including its dosage forms, strengths, brand names, manufacturers, and FDA-listed product records. These are directory records, not sales or prescription volume.

19 companies list 56 Magnesium Oxide product records with the FDA, mostly as tablet; the earliest marketing or approval year on record is 1982. Brand names on the directory include Mag-Ox, Maox, Uro-Mag and 4 more; the rest are generics.

1
Dose forms ⓘ
19
Labelers (makers, repackagers, distributors)
3
Brand names
56
FDA-listed product records ⓘ
1982
Earliest FDA record ⓘ

Also listed with the FDA, not a patient dose form: Powder (4) · Granule (2) — bulk drug substance sold to compounders/manufacturers and multi-item kits. These aren’t counted in the dose-form total above.

Bryant Ranch Prepack20%
Westminster Pharmaceuticals, LLC11%
Dead Sea Periclase9%
Spirit Pharmaceuticals LLC7%
Richmond Pharmaceuticals, Inc.7%
PAR Pharmaceuticals7%
Other makers39%

Share of FDA-listed product records by manufacturer — FDA National Drug Code Directory. Record counts are not sales or prescription volume.

How widely Magnesium Oxide is used (Medicaid data)

A general measure of how commonly Magnesium Oxide is prescribed, based on Medicaid — one of the largest public drug programs. The figure below is prescriptions filled in Q1–Q4 2025, summed across every form and brand of the drug.

Think of this as a proxy for how widely Magnesium Oxide is used, drawn from freely available public data. Medicaid is just one program — these numbers don’t include Medicare, other government coverage, or commercial and cash-pay prescriptions, so real-world use is higher than what’s shown here.

648,844
Medicaid prescriptions filled (Q1–Q4 2025)
$6.3M gross Medicaid reimbursement (before mandatory rebates — net cost is lower)

How commonly is Magnesium Oxide prescribed? Of the 1,601 medications we measure, Magnesium Oxide ranks #230 by Medicaid prescriptions — more than 86% of them.

Where Magnesium Oxide ranks among the drugs we measure · Q1–Q4 2025 · neighbors ±5
Total prescriptions — #230 of 1,601
#225 Mometasone 666,398 Rx #226 Esomeprazole 663,042 Rx #227 Pravastatin 660,709 Rx #228 Rivaroxaban 655,610 Rx #229 Polymyxin B and Trimet... 651,823 Rx #230 Magnesium Oxide 648,844 Rx #231 Alendronate 645,853 Rx #232 Glimepiride 630,394 Rx #233 Doxepin (Insomnia) 628,470 Rx #234 Doxepin (Depression, A... 628,470 Rx #235 Doxepin 628,470 Rx

Utilization by Magnesium Oxide product

Pick a product to see its own Medicaid numbers. Each chip is one clinical product — a specific strength & dosage form as defined by RxNorm — with brand-name and generic versions combined.

The 400 mg oral tablet is the most-dispensed Magnesium Oxide product — about 98% of these Medicaid prescriptions.

magnesium oxide 400 MG Oral Tablet Most dispensed

638,860 Medicaid prescriptions (Q1–Q4 2025) 98% of Magnesium Oxide prescriptions shown $6.1M gross reimbursement (before rebates) ≈ $9.59 per prescription (gross)

Summed across the 4 of 57 listed NDC products with Medicaid activity — every brand and generic of this exact strength & form. RxNorm 198741

magnesium oxide 420 MG Oral Tablet

9,912 Medicaid prescriptions (Q1–Q4 2025) 2% of Magnesium Oxide prescriptions shown $106,095 gross reimbursement (before rebates) ≈ $11 per prescription (gross)

Summed across the 1 of 6 listed NDC products with Medicaid activity — every brand and generic of this exact strength & form. RxNorm 311430

magnesium oxide 440 MG Oral Tablet

72 Medicaid prescriptions (Q2–Q4 2025) <1% of Magnesium Oxide prescriptions shown $29,466 gross reimbursement (before rebates) ≈ $409 per prescription (gross)

Summed across the 1 of 1 listed NDC products with Medicaid activity — every brand and generic of this exact strength & form. RxNorm 2707337

Shares are of the Medicaid prescriptions shown here. Product grouping follows RxNorm (the National Library of Medicine’s drug terminology), so “one product” means one strength & dosage form regardless of manufacturer. Dollar figures are gross Medicaid reimbursement before mandatory rebates — rebates (often large, especially for brand-name drugs) are confidential, so actual net cost to Medicaid is lower than shown.

Source: Medicaid State Drug Utilization Data (CMS), aggregated by generic ingredient — summed across every NDC (all brands, strengths, salt forms and dosage forms) of Magnesium Oxide, and across all states and both fee-for-service and managed-care claims. A general popularity signal; it excludes Medicare, commercial insurance and cash prescriptions, so it is not total U.S. use. Based on the 6 of 64 listed Magnesium Oxide NDCs with Medicaid activity.

Compare Magnesium Oxide products

A representative set of FDA-listed product records for Magnesium Oxide — across manufacturers, strengths, and dosage forms, grouped by form with each product’s manufacturer and how the FDA approved it. The same medicine may be made and packaged by different companies, so a single drug can have many directory entries. (It’s also why a refill can look different — a new shape, color, or box — even though it contains the same medication.)

Showing 56 of 56 products — FDA National Drug Code Directory. See every product, package size and price: browse all 56 Magnesium Oxide NDCs →

Magnesium Oxide side effects reported to the FDA (FAERS)

After a medicine reaches the market, patients, doctors and drugmakers can send the FDA reports of problems they think may be linked to it. Here’s what’s been reported for Magnesium Oxide — a signal of what to watch for, not proof the drug caused it.

The effects most often named in FDA reports that mention Magnesium Oxide are nausea, diarrhoea, fatigue; about 79% of the reports were classed as serious. These are voluntary reports, so they show what people report, not how often it happens.

42,545
Reports mentioning it
79%
Reported as serious
12
Distinct effects shown
Most reported effects
Nausea
3,049
Diarrhoea
2,780
Fatigue
2,596
Dyspnoea
2,207
Pneumonia
2,119
Pyrexia
1,901
Vomiting
1,845
Headache
1,755
Death
1,673
Pain
1,561
Age groups
Elderly · 5,046Adult · 2,812Adolescent · 53Child · 35Infant · 13Neonate · 7

Source: openFDA, from the FDA Adverse Event Reporting System (FAERS). These are voluntary reports — they don’t prove the drug caused the effect, and counts reflect how often something was reported, not how often it actually happens. Reports also often name the very problem the medicine is taken for — a common reason to file one is that the drug didn’t help — so for a pain reliever you may see “pain” high on the list; that points to why the report was filed, not to the drug causing the symptom. This counts every report that lists Magnesium Oxide in any role, so the total runs higher than the FDA’s official dashboard, which counts only cases where the drug is the suspect. For the authoritative figures, see the FDA FAERS Public Dashboard. Always talk to your pharmacist or doctor.

Magnesium Oxide FDA approval history

How Magnesium Oxide went from FDA review to the pharmacy shelf — the key milestones in its regulatory journey.

Magnesium Oxide was first approved by the FDA in 1982 (Brand: IRRIGATING SOLUTION G IN PLASTIC CONTAINER · Baxter Hlthcare); the first generic version was approved in 2022. It remains available in U.S. pharmacies today.

1982
Brand approved
Brand: IRRIGATING SOLUTION G IN PLASTIC CONTAINER · Baxter Hlthcare
2022
First generic approved
Lower-cost ANDA competition begins
2026
Available today
Active in U.S. pharmacies

Source: Drugs@FDA.

Magnesium Oxide recall history

A recall is when a specific batch of a medicine is pulled from the market — usually a manufacturing issue, not a problem with the drug itself. Class I is most serious, Class III least.

The FDA’s enforcement reports list no Magnesium Oxide recalls since July 2021.

✅No Magnesium Oxide recalls on record since July 2021

Source: FDA enforcement (recall) reports, via openFDA; our copy was last updated Sep 24, 2026.

RxNorm Concept Web — From Ingredient to Every Form and Strength

This page starts with one ingredient concept (IN). The branches below show its dose-form concepts (SCDF), then the available clinical drug and strength concepts (SCD). Combination products remain separate concepts with their own pages.

Ingredient (IN) Magnesium Oxide RxCUI 6582 2 dose forms · 11 strengths
  1. Dose form (SCDF) Oral Capsule RxCUI 372691 No current FDA listing
    Clinical drug / strength (SCD) 140 MG RxCUI 198740 400 MG RxCUI 252430 500 MG RxCUI 411877
  2. Dose form (SCDF) Oral Tablet RxCUI 372692 In current FDA listings
    Clinical drug / strength (SCD) 200 MG RxCUI 314113 250 MG RxCUI 311429 400 MG RxCUI 198741 420 MG RxCUI 311430 440 MG RxCUI 2707337 500 MG RxCUI 311431 17900 MG RxCUI 1999991 276000 MG RxCUI 890854

Look up RxCUI 6582 in the RxCUI Atlas →

RxNorm is the U.S. National Library of Medicine’s normalized drug vocabulary. Its concept hierarchy can include forms that are not currently marketed; the status on each branch compares that concept with current FDA listings. RxCUIs identify vocabulary concepts, not individual packages or manufacturers.

Magnesium Oxide brand names

Magnesium Oxide is sold under 7 brand names in the FDA directory — Mag-Ox, Maox, Uro-Mag, Mag-Ox 400 and others. A brand and its generic contain the same active ingredient; the brand name belongs to one company's product.

Mag-Ox Maox Uro-Mag Mag-Ox 400 Phillips' Cramp-free Magmilax Antacid

Who makes Magnesium Oxide: manufacturers and labelers

19 companies list Magnesium Oxide products with the FDA. By number of product records, the largest are Bryant Ranch Prepack, Westminster Pharmaceuticals, LLC, Dead Sea Periclase. Labelers include manufacturers and repackagers; the product in your bottle depends on which one your pharmacy stocks.

Bryant Ranch Prepack 11 Westminster Pharmaceuticals, LLC 6 Dead Sea Periclase 5 Spirit Pharmaceuticals LLC 4 Richmond Pharmaceuticals, Inc. 4 PAR Pharmaceuticals 4 Method Pharmaceuticals, LLC 3 Marlex Pharmaceuticals Inc. 3 Allegiant Health 2 Marlex Pharmaceuticals Inc 2 Endo USA 2 Apnar Pharma Lp 2 Aphena Pharma Solutions - Tennessee, LLC 2 Kesin Pharma 1 Dead Sea Periclase Ltd 1 Belleview Biosciences 1 Belleview Bioscience LLC 1 A-S Medication Solutions 1 Wittman Pharma, Inc. 1

Magnesium Oxide drug class (RxNorm)

Magnesium Oxide belongs to the Magnesium compounds class.

Drug family (ATC) Magnesium compounds, Osmotically acting laxatives, Magnesium

Classified by RxNorm RxClass — the U.S. National Library of Medicine's standardized drug-classification service (Established Pharmacologic Class from the FDA, the ATC drug family from the WHO, and mechanism of action). Reference only, not medical advice.

Sources for this Magnesium Oxide page

Core label, product, RxNorm, safety, and utilization data on this page come from the sources identified below. AI-written, editorial, and licensed sections are labeled separately.

📄
FDA-filed drug labels (SPL) Uses, dosing, warnings & side effects from SPL records retrieved through openFDA; the linked representative set can be verified on DailyMed. ✓ Linked label effective Oct 25, 2018
🏭
Forms, brands & labelersAggregated from ingredient-matched FDA National Drug Code Directory product records for Magnesium Oxide.
📈
Real-world reportsThe FDA Adverse Event Reporting System (FAERS), served through openFDA.
🚨
Recalls & shortagesopenFDA drug-enforcement reports and the FDA drug-shortage database.
🧾 Clinical label set — FDA-filed SPL labels retained for Magnesium Oxide after exact ingredient or ingredient-combination matching and applicable route/form matching
Clinical labels in scope
22
Finished products in the current FDA directory
56
Companies listing them (makers, repackagers, distributors)
19
Linked representative label ⓘ
Aphena Pharma Solutions - Tennessee, LLC
Linked label effective
Oct 25, 2018
Composite sections available
8
Linked SPL Set ID
edabc9e4-60ad-407f-97c8-dfec5ee7eeb1
Linked SPL Document ID
47c92eca-9e78-487b-8c63-14588bb16c71
Open the linked representative label on DailyMed ↗
NDC package records associated with this linked SPL 1

How this page is built

HelloPharmacist combines public FDA and NLM records and does not author the underlying clinical facts. The plain-language sections are written with AI from the FDA-approved label text and reviewed by our pharmacy team before publication. Aphena Pharma Solutions - Tennessee, LLC is the representative DailyMed label linked for verification and dates. This is general education, not medical advice: always talk to your doctor or pharmacist about your own medicines. How we build and review drug pages →