Magnesium hydroxide (MH) is a common over-the-counter compound used for various digestive complaints. It is widely available, often recognized by the brand name Milk of Magnesia. The appropriate daily amount depends entirely on the condition being treated. Understanding the compound’s dual function and adhering to dosage guidelines is crucial for safety and effectiveness.
Understanding the Two Primary Uses
The wide variation in recommended daily doses stems from magnesium hydroxide’s two distinct mechanisms of action. When taken in lower amounts, the compound functions as an antacid, relieving heartburn and indigestion. This effect is achieved through the direct neutralization of stomach acid. Hydroxide ions react with acidic hydrogen ions, forming magnesium chloride and water, which reduces the stomach’s acidity.
When a larger dose is ingested, magnesium hydroxide acts as a saline laxative. This mechanism relies on an osmotic effect within the intestinal tract. Unabsorbed magnesium ions draw water from the body’s tissues into the intestines. This influx of fluid increases the volume of intestinal contents, stimulating peristalsis and promoting a bowel movement. The difference in therapeutic goals—acid neutralization versus osmotic action—dictates the necessary dosage.
Dosage Guidelines for Constipation Relief
Magnesium hydroxide is an effective treatment for occasional constipation, intended only for short-term relief. Adult dosages for the laxative effect are substantially higher than those used for antacid purposes. The maximum daily dose often reaches up to 60 milliliters (mL) of the standard liquid formulation. This volume is equivalent to approximately four tablespoons and contains up to 4,800 milligrams (mg) of magnesium hydroxide, depending on the product’s concentration.
The dose is typically taken once daily, often at bedtime, or in divided doses, and should be followed by a full glass of water to maximize the osmotic action. Since product concentrations vary significantly, always check the specific product label; a concentrated formula might require only 15 to 30 mL. Chewable tablets are also available, with the maximum daily dose often capped at eight tablets per day for adults.
Regardless of the formulation, do not use magnesium hydroxide as a laxative for more than seven consecutive days. Prolonged use without medical guidance can lead to dependence or electrolyte imbalances.
Dosage Guidelines for Antacid Use
When magnesium hydroxide is used to treat heartburn or acid indigestion, the required dose is significantly lower. The goal is immediate, temporary acid neutralization rather than a systemic osmotic effect. A typical adult dose for the liquid suspension ranges from 5 mL to 15 mL (one to three teaspoonfuls). This lower dose minimizes the laxative effect, though it may still occur in sensitive individuals.
This smaller dose can be repeated every four hours as needed for symptom relief. Adults should not exceed four doses within any 24-hour period. For chewable tablets, the typical antacid dose is two to four tablets, also taken every four hours as needed. Users should monitor for any signs of loose stools, even though the total daily intake remains below the amount needed to induce a full laxative effect.
Safety Precautions and Maximum Intake
While magnesium hydroxide is safe for short-term use in healthy individuals, exceeding the maximum daily intake risks hypermagnesemia (magnesium toxicity). Very large doses, typically over 5,000 mg of magnesium per day, are linked to this condition. Symptoms of hypermagnesemia range from mild effects like nausea, vomiting, and muscle weakness, to severe outcomes, including low blood pressure and respiratory depression.
The most important contraindication for magnesium hydroxide use is impaired kidney function, as the kidneys are responsible for excreting excess magnesium. Individuals with kidney disease are unable to efficiently clear the absorbed magnesium, which can rapidly lead to toxic levels in the blood, even at lower doses. Chronic or excessive use should be avoided, especially if the user has any underlying health conditions.
Common side effects, such as abdominal cramping and diarrhea, are usually dose-dependent. Furthermore, magnesium hydroxide can interfere with the absorption of certain medications, including some antibiotics; separate the doses by at least two hours. If symptoms persist beyond the short-term use window of seven days, or if severe side effects occur, medical consultation is necessary.