# Magnesium Hydroxide

**Canonical URL:** https://ingredients.hermeticasuperfoods.com/ingredients/magnesium-hydroxide
**Data Source:** Hermetica Superfoods Ingredient Encyclopedia
**Updated:** 2026-04-04
**Evidence Score:** 2 / 10
**Category:** Mineral
**Also Known As:** Mg(OH)₂, Milk of magnesia, Magnesium dihydroxide, Brucite, Hydrated magnesium oxide, Magnesii hydroxidum, Magnesia hydrate, Magnesium hydrate

## Overview

Magnesium hydroxide is an inorganic magnesium salt that functions as an osmotic laxative by drawing water into the intestinal lumen through osmotic pressure, stimulating peristalsis and bowel movement. It also neutralizes gastric acid by reacting with hydrochloric acid to form magnesium chloride and water, making it effective as an antacid.

## Health Benefits

• Constipation relief: Open-label trials show effectiveness for functional constipation in children over 12 months (PMID: 34961695) - Moderate evidence
• Bladder symptom improvement: 55% of women with sensory urgency/detrusor instability showed improvement vs 25% placebo in RCT (PMID: 9647159) - Moderate evidence
• Opioid-induced constipation prevention: Currently under investigation in 330-patient RCT for cancer patients (PMID: 36915062) - Preliminary evidence
• Pain reduction: Pilot RCT showed significant reduction in capsaicin-induced pain vs saline in first 30 minutes (PMID: 12782534) - Preliminary evidence
• Magnesium supplementation: Provides systemic magnesium with 15% oral bioavailability (PMID: 27412366) - Moderate evidence

## Mechanism of Action

Magnesium hydroxide dissociates in the gut to release Mg²⁺ and OH⁻ ions, which are poorly absorbed, creating an osmotic gradient that pulls water into the intestinal lumen and increases intraluminal pressure, triggering mechanoreceptor-mediated peristalsis. As an antacid, it directly neutralizes hydrochloric acid via the reaction Mg(OH)₂ + 2HCl → MgCl₂ + 2H₂O, raising gastric pH without systemic alkalosis under normal renal function. The mechanism behind bladder symptom improvement is less defined but may involve magnesium's role as a calcium channel antagonist, reducing detrusor smooth muscle excitability by competing with calcium at voltage-gated channels.

## Clinical Summary

An open-label trial (PMID: 34961695) demonstrated magnesium hydroxide effectiveness for functional constipation in children over 12 months of age, representing moderate evidence given the non-blinded design and pediatric-specific population. A randomized controlled trial (PMID: 9647159) found that 55% of women with sensory urgency or detrusor instability reported bladder symptom improvement with magnesium hydroxide versus 25% in the placebo group, a statistically meaningful difference though the sample size limits generalizability. Evidence for antacid use is largely based on well-established pharmacological mechanisms rather than large modern RCTs, as this application predates contemporary trial standards. Overall, constipation relief has the strongest practical evidence base, while bladder and antacid applications are supported by moderate or mechanistic evidence.

## Nutritional Profile

Magnesium Hydroxide [Mg(OH)₂] is an inorganic mineral compound with a molecular weight of 58.32 g/mol. It is not a food ingredient in the traditional macronutrient sense but functions as a concentrated mineral supplement and pharmaceutical agent. Elemental magnesium content: approximately 41.7% by molecular weight, meaning a typical 400–500 mg dose of Mg(OH)₂ delivers approximately 167–208 mg of elemental magnesium. It contains no protein, fat, carbohydrates, or dietary fiber. No vitamins are present. The compound is practically insoluble in water (solubility ~0.00064 g/100 mL at 25°C) but dissolves in the acidic environment of the stomach, forming magnesium chloride (MgCl₂), which is the bioavailable form for absorption in the small intestine. Bioavailability of elemental magnesium from Mg(OH)₂ is estimated at 30–40% under fasting conditions, comparable to magnesium oxide but lower than more soluble forms such as magnesium citrate (~90%) or magnesium glycinate. Absorption occurs primarily in the ileum and large intestine via paracellular transport and active TRPM6/TRPM7 channel-mediated transcellular pathways. At laxative doses (2,400–4,800 mg/day), the osmotic effect predominates over systemic absorption, drawing water into the intestinal lumen. No significant caloric contribution; energy value is 0 kcal per dose.

## Dosage & Preparation

Clinically studied doses include 1080 mg (3 × 360 mg tablets) as a single dose for pharmacokinetic assessment. Studies in constipation used unspecified doses compared to polyethylene glycol over 12 months. Consult a healthcare provider before starting any new supplement.

## Safety & Drug Interactions

Common side effects include diarrhea, abdominal cramping, and electrolyte imbalances, particularly hypermagnesemia in patients with impaired renal function who cannot efficiently excrete excess Mg²⁺ ions. Magnesium hydroxide can reduce the absorption of several medications by altering gastric pH or forming insoluble complexes, including tetracycline antibiotics, fluoroquinolones, bisphosphonates, and iron supplements, so these should be taken at least 2 hours apart. It may potentiate the effects of neuromuscular blocking agents and should be used cautiously alongside drugs that affect magnesium levels, such as loop diuretics or calcineurin inhibitors. It is generally considered safe in pregnancy for short-term constipation relief (FDA historical Category B equivalent), but prolonged use or high doses are discouraged due to risk of neonatal hypermagnesemia.

## Scientific Research

Clinical evidence includes a double-blind RCT in 40 women showing 55% improvement in bladder symptoms (PMID: 9647159), and ongoing trials like the OMAMA study comparing magnesium hydroxide to macrogol for opioid-induced constipation in 330 cancer patients (PMID: 36915062). A pharmacokinetic study confirmed 15% oral bioavailability with peak serum levels at 60-90 minutes (PMID: 27412366).

## Historical & Cultural Context

No historical or traditional medicine system uses were identified in the available research. The compound appears to be primarily a modern pharmaceutical agent without documented traditional applications.

## Synergistic Combinations

Polyethylene glycol 3350, Macrogol, Aluminum hydroxide, Simethicone, Electrolytes

## Known Interactions

| Substance | Severity | Summary | URL |
|---|---|---|---|
| Phenazopyridine | SAFE | 🟢 SAFE — Magnesium Hydroxide and Phenazopyridine can be taken together safely. | https://ingredients.hermeticasuperfoods.com/interactions/phenazopyridine |
| Minoxidil | SAFE | 🟢 SAFE — Magnesium Hydroxide and Minoxidil can be taken together safely. | https://ingredients.hermeticasuperfoods.com/interactions/minoxidil |
| Benzoyl Peroxide | SAFE | 🟢 SAFE — Magnesium Hydroxide and Benzoyl Peroxide can be taken together safely. | https://ingredients.hermeticasuperfoods.com/interactions/benzoyl-peroxide |
| Salicylic Acid | SAFE | 🟢 SAFE — Magnesium Hydroxide and Salicylic Acid can be taken together safely. | https://ingredients.hermeticasuperfoods.com/interactions/salicylic-acid |
| Hydrocortisone | SAFE | 🟢 SAFE — Magnesium Hydroxide and Hydrocortisone can be taken together safely. | https://ingredients.hermeticasuperfoods.com/interactions/hydrocortisone |
| Cranberry Extract | SAFE | 🟢 SAFE — Magnesium Hydroxide and Cranberry Extract can be taken together safely. | https://ingredients.hermeticasuperfoods.com/interactions/cranberry-extract |
| Apple Cider Vinegar | SAFE | 🟢 SAFE — Magnesium Hydroxide and Apple Cider Vinegar can be taken together safely. | https://ingredients.hermeticasuperfoods.com/interactions/apple-cider-vinegar |
| Activated Charcoal | SAFE | 🟢 SAFE — Magnesium Hydroxide and Activated Charcoal can be taken together safely. | https://ingredients.hermeticasuperfoods.com/interactions/activated-charcoal |
| Witch Hazel | SAFE | 🟢 SAFE — Magnesium Hydroxide and Witch Hazel can be taken together safely. | https://ingredients.hermeticasuperfoods.com/interactions/witch-hazel |
| Biotin | SAFE | 🟢 SAFE — Magnesium Hydroxide and Biotin can be taken together safely. | https://ingredients.hermeticasuperfoods.com/interactions/biotin |
| Glucosamine | SAFE | 🟢 SAFE — Magnesium Hydroxide and Glucosamine can be taken together safely. | https://ingredients.hermeticasuperfoods.com/interactions/glucosamine |
| Chondroitin | SAFE | 🟢 SAFE — Magnesium Hydroxide and Chondroitin can be taken together safely. | https://ingredients.hermeticasuperfoods.com/interactions/chondroitin |
| DHEA | SAFE | 🟢 SAFE — Magnesium Hydroxide and DHEA can be taken together safely. | https://ingredients.hermeticasuperfoods.com/interactions/dhea |
| Pregnenolone | SAFE | 🟢 SAFE — Magnesium Hydroxide and Pregnenolone can be taken together safely. | https://ingredients.hermeticasuperfoods.com/interactions/pregnenolone |
| BPC-157 | SAFE | 🟢 SAFE — Magnesium Hydroxide and BPC-157 can be taken together safely. | https://ingredients.hermeticasuperfoods.com/interactions/bpc-157 |
| Testosterone | SAFE | 🟢 SAFE — Magnesium Hydroxide and Testosterone can be taken together safely. | https://ingredients.hermeticasuperfoods.com/interactions/testosterone-rx |
| Estradiol | SAFE | 🟢 SAFE — Magnesium Hydroxide and Estradiol can be taken together safely. | https://ingredients.hermeticasuperfoods.com/interactions/estradiol-rx |
| Progesterone | SAFE | 🟢 SAFE — Magnesium Hydroxide and Progesterone can be taken together safely. | https://ingredients.hermeticasuperfoods.com/interactions/progesterone-rx |
| Desiccated Thyroid | SAFE | 🟢 SAFE — Magnesium Hydroxide and Desiccated Thyroid can be taken together safely. | https://ingredients.hermeticasuperfoods.com/interactions/desiccated-thyroid |
| Growth Hormone | SAFE | 🟢 SAFE — Magnesium Hydroxide and Growth Hormone can be taken together safely. | https://ingredients.hermeticasuperfoods.com/interactions/growth-hormone-rx |

## Frequently Asked Questions

### How long does magnesium hydroxide take to work for constipation?

Magnesium hydroxide typically produces a bowel movement within 30 minutes to 6 hours when taken orally, depending on the dose and individual gut motility. Standard laxative doses range from 2,400 to 4,800 mg for adults, and onset is faster at higher doses due to a more pronounced osmotic effect drawing water into the colon.

### Is magnesium hydroxide the same as milk of magnesia?

Yes, milk of magnesia is a suspension of magnesium hydroxide in water, typically containing 400 mg of Mg(OH)₂ per 5 mL. The liquid formulation improves dispersion and contact with gastrointestinal surfaces, but the active compound and mechanism are identical to tablet forms.

### Can magnesium hydroxide raise magnesium levels in the body?

Under normal renal function, only a small fraction of magnesium hydroxide is absorbed systemically, so it rarely raises serum magnesium to dangerous levels in healthy individuals. However, in people with chronic kidney disease or renal insufficiency, impaired magnesium excretion can lead to hypermagnesemia, with symptoms ranging from nausea and weakness to cardiac arrhythmias at serum levels above 4 mEq/L.

### What is the difference between magnesium hydroxide and magnesium citrate for constipation?

Both are osmotic laxatives, but magnesium citrate is more rapidly and completely absorbed in the small intestine, producing a faster and often more intense laxative effect, while magnesium hydroxide acts more gradually primarily in the colon. Magnesium citrate also provides a higher bioavailable magnesium dose per gram, making it more relevant for correcting magnesium deficiency, whereas magnesium hydroxide is preferred when a gentler, more controlled laxative action is needed.

### Can magnesium hydroxide help with acid reflux or GERD?

Magnesium hydroxide neutralizes gastric hydrochloric acid rapidly via the reaction Mg(OH)₂ + 2HCl → MgCl₂ + 2H₂O, raising intragastric pH and providing symptomatic relief from heartburn within minutes. However, it does not suppress acid secretion the way proton pump inhibitors or H2 blockers do, so it is best used for occasional symptom relief rather than as a primary treatment for chronic GERD, where underlying acid hypersecretion requires more sustained pharmacological management.

### Is magnesium hydroxide safe for children, and what is the appropriate dose?

Magnesium hydroxide is generally recognized as safe for children over 12 months old, with clinical evidence supporting its use for functional constipation in this age group. Dosing should be determined by a pediatrician based on the child's age and weight, as it differs significantly from adult doses. Liquid formulations are typically easier to administer to young children than tablets or capsules.

### Does magnesium hydroxide interact with medications like antibiotics or bisphosphonates?

Yes, magnesium hydroxide can reduce the absorption of certain medications, including fluoroquinolone and tetracycline antibiotics, as well as bisphosphonates used for bone health. It is recommended to take magnesium hydroxide at least 2–4 hours before or after these medications to minimize interaction risk. Always inform your healthcare provider about magnesium hydroxide use when starting new medications.

### Can magnesium hydroxide help with bladder urgency and overactive bladder symptoms?

Clinical research shows that magnesium hydroxide may provide modest benefit for bladder symptoms such as sensory urgency and detrusor instability, with approximately 55% of women experiencing improvement in one randomized controlled trial. However, the evidence is moderate in quality, and it is not yet considered a first-line treatment for overactive bladder. More research is needed to establish optimal dosing and long-term effectiveness for this indication.

---

*Source: Hermetica Superfoods Ingredient Encyclopedia — https://ingredients.hermeticasuperfoods.com*
*License: CC BY-NC-SA 4.0 — Attribution required. Commercial use: admin@hermeticasuperfoods.com*