Magnesium Hydroxide Dosage: How Much to Take and When

Standard Adult Dosage

According to FDA-approved OTC antacid labeling, the typical dosage of magnesium hydroxide for adults and children 12 years and older varies depending on whether it is used as an antacid or laxative.

Antacid Dosing (for Heartburn/Acid Indigestion)

Liquid suspension (400 mg per 5 mL):

• 5-15 mL (1-3 teaspoons) as needed
• Up to 4 times daily
• Maximum: 60 mL (12 teaspoons) in 24 hours

Chewable tablets (typically 311-400 mg):

• 2-4 tablets as needed
• Up to 4 times daily
• Maximum based on specific product strength

Important: Always check specific product label for exact dosing instructions, as concentrations vary.

Laxative Dosing (for Constipation)

Liquid suspension:

• 30-60 mL (2-4 tablespoons) as a single daily dose
• Usually taken at bedtime
• Or 15-30 mL (1-2 tablespoons) divided doses
• Works within 30 minutes to 6 hours

Note: Laxative doses are much higher than antacid doses and produce a strong laxative effect.

Children’s Dosing (Ages 6-11)

According to FDA OTC labeling:

Antacid Use

Ages 6-11 years:

• Consult healthcare provider for appropriate dosing
• Typically 2.5-5 mL (½-1 teaspoon) of liquid
• Up to 4 times daily
• Do not exceed recommended amounts

Laxative Use

Ages 6-11 years:

• 15-30 mL (1-2 tablespoons) as single daily dose
• Or as directed by healthcare provider
• For occasional use only

Children Under Age 6

For children under 6 years:

• Do not use without consulting a healthcare provider
• Dosing must be determined by pediatrician
• Safety and appropriate dosing less established

Maximum Daily Dosage

According to product labeling and FDA guidance:

For antacid use:

• Follow specific product maximum listed on label
• Typically no more than 60 mL liquid (or equivalent tablets) in 24 hours
• Do not exceed 4 doses in 24 hours

For laxative use:

• Do not exceed the single recommended dose
• One dose per day maximum
• Do not use for more than 1 week without medical advice

Important: Using higher doses increases risk of diarrhea and electrolyte disturbances.

When to Take Magnesium Hydroxide

For Heartburn/Acid Indigestion

After meals:

• Most common and effective timing
• Take when symptoms occur after eating
• Can take 1-3 hours after meals if symptoms develop

Before bedtime:

• If experiencing nighttime heartburn
• Take at first sign of symptoms
• May help prevent nighttime reflux

As needed:

• Take whenever heartburn symptoms occur
• No fixed schedule required
• Works within 5-10 minutes

Between meals (less common):

• Can be taken on empty stomach
• Works faster on empty stomach
• But duration may be shorter

For Constipation

Bedtime:

• Most common timing for laxative use
• Allows overnight action
• Usually produces bowel movement in morning
• Works within 30 minutes to 6 hours

Liquid Suspension Dosing

How to take liquid magnesium hydroxide:

1. Shake bottle well before each use (medication settles)
2. Measure dose carefully using:
   • Provided dosing cup
   • Medicine spoon
   • Oral syringe for children
   • Standard measuring spoon (not regular spoon)
3. Can be taken:
   • Straight from measuring device
   • Mixed with small amount of water or milk
   • Followed by water
4. Timing: With or without food

Important: Do not use kitchen spoons - they vary in size and lead to inaccurate dosing.

Chewable Tablets

How to take chewable tablets:

• Chew tablets thoroughly before swallowing
• Do not swallow whole
• Can take with or without water
• Water may help with distribution in stomach
• Can take with or without food

Advantages:

• More portable than liquid
• No measuring required
• Good for travel or work

With or Without Food

According to antacid pharmacology:

Magnesium hydroxide can be taken with or without food:

On empty stomach:

• Works faster (5-10 minutes)
• Shorter duration (30-60 minutes)
• Good for immediate relief

With or after food:

• Slightly slower onset (10-20 minutes)
• Longer duration (1-3 hours)
• Food buffers and extends effect
• Often more effective timing

Most people take it when symptoms occur, regardless of meals.

How Often Can You Take It?

For antacid use:

• As needed when symptoms occur
• Can dose every few hours if needed
• Maximum 4 times in 24 hours
• Minimum 2-3 hours between doses recommended

For laxative use:

• Once daily maximum
• Do not repeat dose in same day
• Allow time for laxative effect (30 minutes to 6 hours)

Duration of Use

Antacid Use

Short-term, occasional use is intended:

• For occasional heartburn symptoms
• Not for daily ongoing use
• Safe to use as needed when symptoms occur

If using more than 2 weeks: According to FDA OTC labeling, if symptoms persist for more than 2 weeks, consult a healthcare provider. Frequent symptoms may indicate GERD or other conditions requiring different treatment.

Laxative Use

Very short-term only:

• For occasional constipation
• Do not use for more than 1 week
• Chronic laxative use can cause dependency
• See healthcare provider if constipation persists

Medication Timing Conflicts

Important timing considerations:

According to drug interaction references, magnesium hydroxide can interfere with absorption of many medications:

Separate by at least 2 hours from:

• Tetracycline antibiotics
• Fluoroquinolone antibiotics (ciprofloxacin, levofloxacin)
• Iron supplements
• Thyroid medications (levothyroxine)
• Bisphosphonates (alendronate, risedronate)
• Digoxin (heart medication)
• Some HIV medications

Recommended approach:

• Take prescription medications first thing in morning
• Take magnesium hydroxide 2 hours later
• Or take medications 2 hours after magnesium hydroxide
• Discuss with pharmacist about your specific medications

Adjusting Dosage Based on Response

If relief is inadequate:

• May increase to maximum recommended dose
• Check if taking at optimal time (after meals)
• Consider whether liquid form works better than tablets
• If maximum dose doesn’t help, consult healthcare provider
• Symptoms may require different treatment

If you get adequate relief with less:

• Can use lower doses
• Perfectly acceptable to use minimum effective amount
• No need to take maximum if not needed

If experiencing diarrhea:

• Reduce dose
• Consider switching to calcium carbonate
• Take with food to slow absorption
• Consult healthcare provider if persists

What If It Does Not Work?

If magnesium hydroxide at appropriate doses does not relieve symptoms:

Consider:

• Are you using adequate dose?
• Have you tried liquid form (may work faster)?
• Is this truly heartburn, or another type of discomfort?
• Are symptoms occurring very frequently (2+ times per week)?

Do not:

• Exceed maximum recommended doses
• Use continuously for more than 2 weeks without medical advice
• Assume more medication will solve the problem

Instead: According to FDA guidance and medical practice guidelines:

• Try H2 blocker (famotidine) for more persistent symptoms
• Consider PPI (omeprazole, esomeprazole) for frequent symptoms
• Consult healthcare provider for proper evaluation
• May need diagnostic testing if symptoms persist

Switching Between Antacid and Laxative Use

Using same product for different purposes:

If using as antacid regularly:

• Can use laxative dose if constipation develops
• But not on same day as multiple antacid doses
• Allow 24 hours between last antacid dose and laxative dose

If using as laxative:

• Can use antacid doses on other days
• Do not combine antacid and laxative doses in same day
• Wait until laxative effect has resolved

Special Dosing Considerations

Pregnancy

Pregnancy dosing: According to medical practice guidelines:

• Standard adult antacid doses are generally safe
• Short-term, occasional use
• Avoid high-dose or chronic use
• Consult obstetrician before using as laxative
• Other laxatives may be preferred during pregnancy

Older Adults

Seniors:

• Same adult dosing
• But use with caution if kidney function is reduced
• Monitor for diarrhea or electrolyte issues
• Check with healthcare provider if using regularly

Kidney Disease

Impaired kidney function: According to medical literature:

• Avoid regular use with moderate to severe kidney disease
• Magnesium can accumulate
• Occasional single use may be acceptable with mild kidney disease
• Consult healthcare provider before use
• Calcium carbonate may be safer alternative

Missed Dose

Because magnesium hydroxide is taken as needed for symptoms:

• The concept of a missed dose typically does not apply
• Take when symptoms occur
• Do not double up to make up for “missed” doses
• Do not exceed maximum daily amount

Combination Products

Many products combine magnesium hydroxide with other ingredients:

Magnesium Hydroxide + Aluminum Hydroxide

Common combinations (Maalox, Mylanta):

• Follow combination product instructions
• Different dosing than single-ingredient products
• Balances laxative and constipating effects
• Check label for magnesium content

Magnesium Hydroxide + Simethicone

For gas and heartburn:

• Follow product-specific dosing
• Adds anti-gas effect
• May have different recommended doses

Always check the total magnesium hydroxide content when using combination products to avoid excessive doses.

Storage and Handling

Liquid magnesium hydroxide:

• Store at room temperature (68-77°F)
• Do not freeze
• Shake well before each use
• Keep bottle tightly closed
• Protect from light
• Check expiration date
• Discard if expired or if appearance changes

Chewable tablets:

• Store at room temperature
• Keep in original container
• Protect from moisture
• Keep tightly closed

Keep out of reach of children - overdose can cause serious effects.

Signs of Overuse

Excessive magnesium can cause:

• Severe diarrhea
• Dehydration
• Nausea
• Muscle weakness
• Confusion
• Low blood pressure
• Irregular heartbeat

If these occur:

• Stop medication immediately
• Drink fluids to prevent dehydration from diarrhea
• Seek medical attention if symptoms are severe
• Especially important for those with kidney disease

When to Contact a Healthcare Provider

Consult a healthcare provider if:

• Symptoms persist for more than 2 weeks of use
• Need to use antacid daily for extended period
• Experiencing severe or worsening symptoms
• Developing other symptoms (weight loss, difficulty swallowing)
• Have kidney disease and considering use
• Taking multiple medications and unsure about timing
• Experiencing persistent diarrhea from the medication
• Constipation does not improve within 1 week of laxative use

Comparison with Other Antacid Dosing

Typical adult dosing frequency:

Antacid	Typical Dose	Frequency
Magnesium hydroxide	5-15 mL liquid	Up to 4 times daily
Calcium carbonate	500-1,500 mg	Up to 4 times daily
Aluminum hydroxide	10-30 mL	Up to 6 times daily
Sodium bicarbonate	325-650 mg	Every 4 hours

All antacids work quickly but have short duration, requiring multiple daily doses for ongoing symptoms.

Related Information

• Magnesium Hydroxide Overview
• Magnesium Hydroxide Side Effects
• How Long Does Magnesium Hydroxide Take to Work?
• Calcium Carbonate vs Magnesium Hydroxide Comparison
• Calcium Carbonate Dosage Information

Sources

This information is based on FDA-approved OTC antacid and laxative monographs, product labeling for magnesium hydroxide products, clinical dosing guidelines, and peer-reviewed medical literature.