Magnesium oxide
MAG-OX
Pronunciation: mag-NEE-zee-um OX-ide
What it isMagnesium salt acting as an osmotic laxative and repletion agent; constipation and hypomagnesemia.
Why this oneHigh elemental magnesium but poor absorption makes it more reliable as a laxative than as repletion.
What limits itDiarrhea is dose-limiting, and magnesium can accumulate dangerously when kidney function is impaired.
Magnesium oxide prescription history
Animated chart of estimated U.S. prescriptions per year, Constipation meds (1900–2026). Magnesium oxide enters in 1950 (estimated).
Principal riskDiarrhea; accumulation in renal impairment
Classes and tags
Clinical profile
Defining liabilityDiarrhea; hypermagnesemia with impaired clearance or bowel dysfunction
FDA label
Read the full label on DailyMed ↗
NO BOXED WARNINGS
| FDA dosing | Population | Start | Target | Max |
|---|---|---|---|---|
| Antacid | Adults | 1–2 tablets QD | 1–2 tablets QD | 2 tablets/day unless directed by a physician |
Renal Undefined
Hepatic Undefined
Label does not state tablet strength (mg).
Available strengths
- tab 253, 400, 420, 440 mg
- tab 241.3 mg/1000 mg
Pregnancy Undefined
Lactation Undefined
Cost
| Strength | #/mo | generic $/mo | CostPlus | |
|---|---|---|---|---|
| 253 mg | tab | 30 qd | $1.15 | not offered |
| 400 mg | tab | 30 qd | $1.04 | not offered |
| 420 mg | tab | 30 qd | not offered | |
| 440 mg | tab | 30 qd | not offered | |
| 241.3 mg/1000 mg | tab | 30 qd | not offered |
Other forms: Magnesium (Mg2+)
Open Magnesium oxide in the interactive console ↗
Self-check
- Why is magnesium oxide more reliable as a laxative than for repletion?
Poor absorption despite high elemental magnesium. - What effect limits magnesium oxide dosing?
Diarrhea.