Magnesium Hydroxide

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.

Origin & History

Magnesium hydroxide is an inorganic compound with the formula Mg(OH)₂, classified as a mineral salt that occurs naturally as the mineral brucite. It is primarily produced industrially by reacting magnesium salts with a base like sodium hydroxide, and is commonly available as a white powder or suspension for oral use.

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.

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

How It Works

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.

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).

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.

Preparation & Dosage

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.

Synergy & Pairings

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

Safety & 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.