Messi Biology states that pharmaceutical-grade magnesium hydroxide is a high-purity inorganic compound with Mg(OH)₂ as its main component, produced and inspected in accordance with pharmaceutical raw material quality management requirements. It serves as a core raw material for antacids and saline laxatives, and its quality must strictly comply with mainstream pharmacopeia standards such as the Chinese Pharmacopeia (ChP), the United States Pharmacopeia (USP), and the European Pharmacopeia (EP).
The molecular formula of magnesium hydroxide is Mg(OH)₂, with a molecular weight of 58.32 and a CAS number of 1309-42-8. It appears as a white or off-white amorphous powder, which is almost insoluble in water and soluble in dilute acids. Its pharmacological activity stems from its weak alkaline properties: upon entering the stomach, it neutralizes hydrochloric acid via the reaction Mg(OH)₂ + 2HCl → MgCl₂ + 2H₂O. Each gram can neutralize approximately 25 mmol of hydrochloric acid, thereby raising gastric pH and alleviating symptoms such as heartburn, acid reflux, and indigestion. Because the reaction is mild and does not generate carbon dioxide gas, it avoids gastric distension and belching, nor does it trigger “rebound acid secretion,” an advantage it holds over sodium bicarbonate and calcium carbonate. When administered in larger doses (e.g., around 5g per dose), unabsorbed magnesium ions create a hypertonic environment in the intestinal tract, “drawing” water into the intestinal lumen to soften feces and promote peristalsis, thus exerting a mild osmotic laxative effect—commonly known as the use of “milk of magnesia.”
The dividing line between pharmaceutical-grade and ordinary industrial-grade magnesium hydroxide lies primarily in three links: “raw materials—process—testing.” Pharmaceutical-grade production predominantly adopts the high-purity magnesium salt precipitation method: using magnesium chloride or magnesium sulfate with a purity of ≥99.9% as raw materials, dissolving them in ultrapure water, adding high-purity chelating agents (such as EDTA) to remove iron and heavy metal ions, and then adjusting the pH to 9.0–9.5 using electronic-grade aqueous ammonia to generate precipitation. Following centrifugal separation, ultrafiltration membrane washing, vacuum drying, and air-jet milling, a final product with a purity of 99.5%–99.8% is obtained, with total heavy metals controlled below 0.0005%. In contrast, industrial-grade products obtained by grinding natural brucite typically have a purity of less than 90%, making impurities difficult to remove, and are only suitable for non-pharmaceutical scenarios such as wastewater treatment and flame-retardant fillers.
The downstream applications of pharmaceutical-grade magnesium hydroxide are concentrated in three major directions: first, antacid preparations, such as magnesium hydroxide suspension (milk of magnesia) and chewable tablets, used for the symptomatic relief of excessive stomach acid and gastroesophageal reflux; second, laxative preparations, used for occasional constipation, postoperative bowel clearance, or bowel preparation prior to colonoscopy; third, pharmaceutical excipients and magnesium supplementation agents, serving as pH adjusters, fillers, and glidants in tablets, or combined with vitamins to formulate magnesium supplementation products.
From high-purity raw materials to strict pharmacopeia indicators, and further to gentle two-way pharmacological actions, pharmaceutical-grade magnesium hydroxide uses a seemingly ordinary inorganic molecule to bridge the gap between chemistry and clinical practice—which is why it has long remained a core raw material for gastrointestinal OTC drugs.