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

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

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

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

Pregnancy OTC label: if pregnant, ask a health professional before use.

Lactation OTC label: if breast-feeding, ask a health professional before use.

NO BOXED WARNINGS

Principal riskDiarrhea; magnesium accumulation in renal impairment

Direct muscarinic antagonism0 / 4