Magnesium Hydroxide for Constipation (Phillips’ Milk of Magnesia)

About Magnesium Hydroxide Tablets/Capsules and Liquid

Magnesium hydroxide, commonly known as

Phillips’ Milk of Magnesia

, is an over-the-counter osmotic laxative used primarily for relieving occasional constipation. It works by drawing water into the intestines, softening stool, and promoting bowel movements, typically within 30 minutes to 6 hours. This saline laxative is available in liquid suspension form, which is the traditional Milk of Magnesia, as well as tablets or capsules for convenience. Unlike stimulant laxatives, it gently increases water content in the bowel without harsh contractions, making it suitable for short-term use in adults and children over certain ages.

The medication belongs to the saline laxative class, where poorly absorbed magnesium salts retain water in the colon, easing passage of stool. It’s also used as an antacid for indigestion and heartburn by neutralizing stomach acid. However, for constipation, its primary mechanism is osmotic: magnesium hydroxide pulls fluid into the intestines, hydrating hard stools and stimulating peristalsis. Clinical evidence supports its efficacy; studies show magnesium salts like hydroxide and oxide improve stool frequency, consistency, and colonic transit time compared to placebo.

Phillips’ Milk of Magnesia is favored for its rapid action and safety profile when used as directed. It’s not intended for chronic constipation, where underlying causes should be investigated. Always consult a healthcare provider for persistent symptoms.

Key facts

• **Active ingredient**: Magnesium hydroxide (typically 400mg/5ml in suspension).
• **Onset of action**: 30 minutes to 6 hours for constipation relief.
• **Forms**: Liquid (original Milk of Magnesia), tablets, capsules.
• **Best time to take**: Bedtime with a full glass of water for morning results.
• **Duration**: Short-term use only (up to 1 week unless advised by doctor).
• **Not for**: Long-term use, chronic constipation, or patients with kidney issues.

About constipation

Constipation is characterized by infrequent bowel movements (fewer than 3 per week), hard stools, straining, or a sense of incomplete evacuation. It affects nearly everyone occasionally, often due to diet low in fiber, dehydration, inactivity, or medications. Chronic constipation may signal issues like irritable bowel syndrome (IBS), hypothyroidism, or medications such as opioids.

Symptoms include abdominal bloating, discomfort, and reduced quality of life. Risk factors: age (elderly), low-fiber diet, sedentary lifestyle, pregnancy, and certain drugs. Diagnosis uses Bristol Stool Scale; types 1-2 indicate constipation. Treatment starts with lifestyle changes: high-fiber diet (25-30g/day), hydration (8 glasses water), exercise. If ineffective, laxatives like magnesium hydroxide are next.

How and when to take Magnesium Hydroxide

Dosage

For adults and children 12+: 30-60ml (regular strength) or 15-30ml (concentrated) at bedtime, not exceeding 120ml/day. Children 6-11: half adult dose; 2-5: quarter; under 2: consult doctor. Tablets: 8 tablets (max) daily. Start low to assess tolerance.

Age Group	Initial Dose	Max Daily Dose
Adults/12+	30-60ml liquid or 4 tablets	120ml or 8 tablets
6-11 years	15-30ml	60ml
2-6 years	5-15ml	30ml
Under 2	Consult doctor	N/A

How to take it

• Shake liquid well; take with full 8oz glass of water/juice.
• Tablets/capsules: Swallow whole with water.
• Bedtime dosing ideal for overnight action.
• Space 2 hours from other meds, vitamins, antibiotics.

When to take

Take for occasional constipation only. Expect results in 0.5-6 hours. If no bowel movement in 6 hours, do not repeat same day. Use for max 7 days; see doctor if persists.

Common questions

How long does it take to work?

Typically 30min-6hrs; faster if dehydrated stools.

Does it cause diarrhea?

Yes, overdose can; start low.

Can I take it daily?

No, short-term only to avoid dependency/electrolyte loss.

Cautions

• Avoid if kidney disease, bowel obstruction, appendicitis symptoms.
• Pregnancy/breastfeeding: Generally safe, consult doctor.
• Interactions: Tetracyclines, bisphosphonates, PPIs reduce efficacy.
• Monitor for hypermagnesemia in elderly/renal impairment.

Side effects

Common: Loose stools, cramps, nausea. Rare: Electrolyte imbalance, hypermagnesemia (symptoms: drowsiness, low BP). Stop if severe. Magnesium hydroxide is poorly absorbed, minimizing systemic effects.

Pregnancy and breastfeeding

Category B; safe in moderation. Limited data, but used historically. Consult provider.

Other medicines, food and drink, alcohol

Space from other drugs 2hrs. No food/alcohol interactions, but hydrate well.

Common side effects

• Diarrhea/cramping (dose-related).
• Gas, bloating.
• Manage: Reduce dose, hydrate.

Serious side effects

Muscle weakness, irregular heartbeat: Seek emergency care (hypermagnesemia).

Taking with other medicines and herbal supplements

Interacts with antibiotics, iron, PPIs. Inform doctor/pharmacist.

Analgesics

Safe with painkillers, but monitor constipation from opioids.

General notes

Lifestyle: Fiber, water, exercise first.

Alternatives

Laxative	Type	Onset	Best For
Mag Oxide	Osmotic	>6hrs	Chronic, gentle
Mag Citrate	Osmotic	<6hrs	Moderate
PEG (Miralax)	Osmotic	1-3 days	Daily use

Frequently Asked Questions

Is Milk of Magnesia safe for daily use?

No, for occasional use only to prevent dependency and imbalances.

Can children take it?

Yes, age-appropriate doses; under 2: doctor approval.

What if it doesn’t work?

Consult doctor; may need evaluation for chronic issues.

Does it interact with PPIs?

Yes, reduces efficacy; space doses.

Best magnesium for constipation?

Hydroxide for fast relief; citrate moderate.