Magnesium Hydroxide Dosage Chart
Magnesium hydroxide, sold as Milk of Magnesia, is an OTC laxative and antacid. As a laxative, it draws water into the intestines to soften stool. As an antacid, it neutralizes stomach acid. It is not typically used for daily magnesium supplementation due to its strong osmotic laxative effect.
Magnesium Hydroxide Dosage by Age Group
| Age Group | Age Range | Dose Range | Notes |
|---|---|---|---|
| Children (6–11 yr) — laxative | 6–11 years | 1200–2400 mg | As liquid Mg(OH)₂; 400 mg/5 mL |
| Adolescents (12–17 yr) — laxative | 12–17 years | 2400–4800 mg | Same as adult dose |
| Adults — laxative | 18–64 years | 2400–4800 mg | Usually 30–60 mL liquid once daily |
| Adults — antacid | 18–64 years | 400–1200 mg | With meals and at bedtime |
| Seniors (65+) — laxative | 65+ years | 1200–2400 mg | Start at lower end; monitor for electrolyte effects |
When and how to take Magnesium Hydroxide
For laxative use: take at bedtime or with a full glass of water in the morning. Antacid: take between meals and at bedtime. Effects typically occur in 6–12 hours.
Available Forms
Standard OTC form. 400 mg magnesium hydroxide per 5 mL (1 tsp).
Shake well before use; regular vs. concentrated formulas differ
Convenient; primarily antacid use.
311 mg per tablet typical
Safety Cautions
- Not for daily use as a magnesium supplement — osmotic laxative effect is too strong.
- Do not use for more than 7 consecutive days without physician guidance.
- Kidney disease is a contraindication — magnesium cannot be excreted and toxicity can occur.
- May reduce absorption of certain medications (bisphosphonates, quinolone antibiotics, levothyroxine) — space by 2 hours.
- Children under 6 years: use only under physician supervision.
Frequently Asked Questions
How much Milk of Magnesia (magnesium hydroxide) should I take for constipation?
Adults typically take 30–60 mL of regular-strength Milk of Magnesia (approximately 2,400–4,800 mg magnesium hydroxide) once daily at bedtime. Use the lowest effective dose. Bowel movement usually occurs within 6–12 hours.
Is magnesium hydroxide the same as Milk of Magnesia?
Yes. Milk of Magnesia is the brand name for a suspension of magnesium hydroxide in water. Regular strength contains 400 mg magnesium hydroxide per 5 mL; concentrated formulas contain 800 mg per 5 mL.
Can I use magnesium hydroxide as a daily magnesium supplement?
No. Magnesium hydroxide is primarily an osmotic laxative and antacid, not a bioavailable supplement form. For daily magnesium supplementation, use magnesium citrate, glycinate, or malate instead. The laxative dose far exceeds what is needed for supplementation.
Sources & References
- FDA drug label: Magnesium Hydroxide Suspension
- NIH ODS — Magnesium Consumer Fact Sheet
- Medline Plus: Magnesium Hydroxide