Mg hydroxide
MILK OF MAG
What it isMagnesium salt acting as an osmotic laxative and antacid; constipation and dyspepsia.
Why this oneIt works within hours and doubles as an antacid, which is why milk of magnesia persists over the counter.
What limits itDiarrhea is the dose-limiting effect, and magnesium accumulates dangerously in renal impairment.
FDA-approved for
- constipation / antacid
FDA label
Read the full label on DailyMed ↗
| FDA dosing | Population | Start | Target | Max |
|---|---|---|---|---|
| Antacid — heartburn, sour stomach, acid indigestion | Adults & peds >=12 yr | 30 mL (2400 mg) PRN | 30 mL up to BID | 60 mL (2 doses)/24 h; <12 yr ask a doctor |
| Saline laxative — occasional constipation | Adults & peds >=12 yr | 30 mL QD | 30-60 mL QD (single or divided doses) | 60 mL/24 h; <12 yr ask a doctor |
Renal Ask a doctor before use in kidney disease or a magnesium-restricted diet (OTC label)
Hepatic Undefined
Laxative use generally produces a bowel movement in 1/2 to 6 hours
Instructions
- Shake well before use
- Laxative use: drink a full glass (8 oz) of liquid with each dose
- Antacid use: do not use the maximum dosage for more than 2 weeks except under advice/supervision of a doctor
- Stop laxative use and ask a doctor if rectal bleeding or no bowel movement after use, or if a laxative is needed for more than 1 week
Available strengths
- susp 1200 mg/15 mL
- susp 2400 mg/30 mL
- susp 400 mg/5 mL
- susp 80 mg/mL
- cap 800 mg
- chew tab 400, 600, 1200 mg
- sol 1200 mg/15 mL
Cautions
- Kidney disease or a magnesium-restricted diet — ask a doctor before use
- Laxative use with abdominal pain, nausea, vomiting, or a sudden change in bowel habits lasting >2 weeks — ask a doctor first
- May interact with certain prescription drugs — ask a doctor or pharmacist
- Rectal bleeding or failure to produce a bowel movement — stop use (possible serious condition)
- Antacid use may cause a laxative effect
Adverse reactions
- Laxative effect (OTC label lists no other adverse reactions)
Pregnancy OTC label: if pregnant, ask a health professional before use.
Lactation OTC label: if breast-feeding, ask a health professional before use.
Cost
| Strength | #/mo | generic $/unit | CostPlus | |
|---|---|---|---|---|
| 1200 mg/15 mL | susp | per unit | $0.01/mL | not offered |
| 2400 mg/30 mL | susp | per unit | not offered | |
| 400 mg/5 mL | susp | per unit | not offered | |
| 80 mg/mL | susp | per unit | not offered |
Available combined with: Al/Mg antacid (MAALOX / MYLANTA)
NO BOXED WARNINGS
Principal riskDiarrhea; magnesium accumulation in renal impairment
Classes and tags
Clinical profile
Defining liabilityHypermagnesemia with excessive exposure or impaired renal elimination