What are the side effects of milk of magnesia (magnesium hydroxide)?

Side Effects of Milk of Magnesia (Magnesium Hydroxide)

The most common side effects of milk of magnesia include gastrointestinal symptoms such as diarrhea, nausea, and vomiting, while severe adverse effects can occur with overdose or in patients with renal impairment, including potentially life-threatening hypermagnesemia. 1, 2

Common Side Effects

• Gastrointestinal effects:

  • Diarrhea (most common)
  • Abdominal cramping
  • Nausea
  • Vomiting
  • Abdominal discomfort 1, 2

• Electrolyte and metabolic disturbances:

  • Hypophosphatemia
  • Fluid abnormalities
  • Electrolyte imbalances 3

Severe Side Effects and Toxicity

Hypermagnesemia can occur with excessive use or in patients with impaired renal function, presenting as:

Cardiovascular effects (by serum magnesium level):

• ECG changes (prolonged PR, QRS, and QT intervals) at levels of 2.5-5 mmol/L
• AV nodal conduction block
• Bradycardia
• Hypotension
• Cardiac arrest at levels of 6-10 mmol/L 3, 4

Neurological effects:

• Loss of tendon reflexes
• Sedation
• Severe muscular weakness
• Respiratory depression at levels of 4-5 mmol/L 3

Other serious complications:

• Paralytic ileus (intestinal smooth muscle dysfunction) 5
• Respiratory failure 4
• Hypothermia 4

Risk Factors for Adverse Effects

High-risk populations:

1. Patients with renal impairment

   • Individuals with kidney disease should avoid magnesium-containing products 1, 2
   • Patients with creatinine clearance <20 mg/dL should use with caution 1

2. Patients with bowel obstruction

   • Risk of severe hypermagnesemia even with normal renal function 6

3. Elderly patients

   • More susceptible to adverse effects due to age-related decline in renal function

4. Patients on certain medications

   • Those taking medications that may interact with magnesium 1
   • Patients on diuretics 1

Monitoring and Prevention

• For short-term use as a laxative, monitoring is generally not required in healthy individuals
• For patients with risk factors or on long-term therapy:
  • Monitor serum magnesium levels periodically
  • Watch for early signs of hypermagnesemia (flushing, sedation, muscle weakness)
  • More frequent monitoring for patients on diuretics or with cardiac conditions 1

Treatment of Magnesium Toxicity

1. Discontinue magnesium-containing products immediately

2. For severe hypermagnesemia:

   • Calcium administration (calcium chloride 5-10 mL of 10% solution or calcium gluconate 15-30 mL of 10% solution IV over 2-5 minutes) 3
   • Intravenous fluids
   • Diuretics (furosemide)
   • Hemodialysis in severe cases 4

Important Warnings and Precautions

• Stop use and consult a doctor if:

  • Rectal bleeding occurs
  • No bowel movement occurs after using the product
  • Symptoms persist for more than one week 2

• Consult a healthcare provider before use if:

  • You have kidney disease
  • You are on a magnesium-restricted diet
  • You have stomach pain, nausea, or vomiting
  • You experience a sudden change in bowel habits lasting over 14 days 2
  • You are taking prescription medications 2
  • You are pregnant or breastfeeding 2

Remember that while milk of magnesia is generally safe for short-term use in healthy individuals, it can cause serious adverse effects in certain populations, particularly those with impaired renal function or bowel obstruction.