Milk of Magnesia Dosing Frequency
Milk of magnesia can be given once or twice daily, with a maximum of 60 mL total per 24-hour period when used as a laxative. 1
FDA-Approved Dosing Guidelines
As a Laxative (Primary Use for Constipation)
Adults and children ≥12 years: 30-60 mL (2-4 tablespoons) per day
- May be taken once daily (preferably at bedtime) or in divided doses
- Maximum: 60 mL in 24 hours
- Must drink a full 8 oz glass of liquid with each dose 1
Children 6-11 years: 15-30 mL (1-2 tablespoons) per day
- Maximum: 30 mL in 24 hours 1
As an Antacid (Different Indication)
- Adults and children ≥12 years: 5-15 mL (1-3 teaspoons) as needed
- Can be taken multiple times throughout the day
- Do not exceed maximum recommended daily dose in 24 hours 1
Clinical Context from Guidelines
The 2023 AGA-ACG guidelines recommend magnesium oxide (the active ingredient in milk of magnesia) as a conditional recommendation for chronic idiopathic constipation 2. While clinical trials used 1,500 mg daily doses, lower doses of 400-500 mg daily are commonly used in clinical practice 2. The guidelines note that response should guide dose titration 2.
Important Caveats
- Renal insufficiency: Avoid in patients with creatinine clearance <20 mg/dL due to hypermagnesemia risk 2
- Duration: While studied for 4 weeks in trials, longer-term use is appropriate 2
- Titration: Start at lower doses and increase based on symptom response 2
Practical Application
For constipation management, once-daily dosing at bedtime is the standard approach, with the option to split into twice-daily dosing if needed for symptom control, always staying within the 60 mL/day maximum 1. The twice-daily regimen (30 mL BID) has been used successfully in postoperative settings 3, demonstrating safety and efficacy of divided dosing.