Magnesia, Magnesia Magma, Milk of Magnesia, M.O.M.
Classifications: saline cathartic; antacid;
Therapeutic: laxative
; antacid
Pregnancy Category: B


311 mg tablets; 400 mg/5 mL, 800 mg/5 mL suspension


Aqueous suspension of magnesium hydroxide with rapid and long-acting neutralizing action. May cause slight acid rebound. Causes osmotic retention of fluid, which distends colon, resulting in mechanical stimulation of peristaltic activity.

Therapeutic Effect

Acts as antacid in low doses and as mild saline laxative at higher doses.


Short-term treatment of occasional constipation, for relief of GI symptoms associated with hyperacidity, and as adjunct in treatment of peptic ulcer. Also has been used in treatment of poisoning by mineral acids and arsenic, and as mouthwash to neutralize acidity.


Abdominal pain, nausea, vomiting, chronic diarrhea, severe kidney dysfunction, fecal impaction, intestinal obstruction or perforation, rectal bleeding, colostomy, ileostomy, children <2 y is not established.

Cautious Use

Older adults, renal impairment, renal disease; pregnancy category B, lactation.

Route & Dosage

Adult: PO 2.4–4.8 g (30–60 mL)/d in 1 or more divided doses
Child: PO 2–5 y, 0.4–1.2 g (5–15 mL)/d in 1 or more divided doses; 6–11 y, 1.2–2.4 g (15–30 mL)/d in 1 or more divided doses


  • Shake bottle well before pouring to assure mixing of suspension.
  • Follow drug with at least a full glass of water to enhance drug action for laxative effect. Administer in the morning or at bedtime. Most effective when taken on an empty stomach.
  • Store at 15°–30° C (59°–86° F) in tightly covered container. Slowly absorbs carbon dioxide on exposure to air. Avoid freezing.

Adverse Effects (≥1%)

GI: Nausea, vomiting, abdominal cramps, diarrhea. Urogenital: Alkalinization of urine. Body as a Whole: Weakness, lethargy, mental depression, hyporeflexia, dehydration, coma. Metabolic: Electrolyte imbalance with prolonged use. CV: Hypotension, bradycardia, complete heart block and other ECG abnormalities. Respiratory: Respiratory depression.


Drug: Milk of Magnesia decreases absorption of chlordiazepoxide, dicumarol, digoxin, isoniazid, quinolones, tetracyclines.


Absorption: 15–30% of magnesium is absorbed. Onset: 3–6 h. Distribution: Small amounts distributed in saliva and breast milk. Elimination: In feces; some renal excretion.

Nursing Implications

Assessment & Drug Effects

  • Evaluate the patient's continued need for drug. Prolonged and frequent use of laxative doses may lead to dependence. Additionally, even therapeutic doses can raise urinary pH and thereby predispose susceptible patients to urinary infection and urolithiasis.
  • Lab tests: Monitor serum magnesium with signs of hypermagnesemia such as bradycardia (see Appendix F), especially with frequent use or any degree of renal impairment.

Patient & Family Education

  • Investigate the cause of persistent or recurrent constipation or gastric distress with physician.

Common adverse effects in italic, life-threatening effects underlined; generic names in bold; classifications in SMALL CAPS; Canadian drug name; Prototype drug

© 2006-2022 Last Updated On: 11/16/2022 (0)
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