Magnesium hydroxide (Mg(OH)2), known as milk of magnesia when it is placed in an aquaeous solution, is a drug for both hyperacidity (indicated by sour stomach or heartburn) and constipation. While the same substance is used for both of these conditions, milk of magnesia dosage between them is different. One does not use the dosage required for constipation in a case of hyperacidity, and the same thing goes for the other way around. The following will explain why this is the case.
Milk of magnesia relies on two of its properties for its pharmacology:
- That it is a basic (alkaline) substance to counter the stomach’s acidity (specifically, the hydroxide ions attached to the magnesium). In high school chemistry it is taught that basic substances (those with a pH greater than 7) can neutralize acidic substances (those with a pH less than 7). The hydroxyl component counteracts and neutralizes the hydrogen ions that are in excess inside the stomach, turning into water in the process. The excess acidity is therefore eliminated, and the stomach wall will no longer be damaged, leading to relief of symptoms.
- That the magnesium ions generated when the magnesium separates from the two hydroxide components in water is poorly absorbed by the intestines. An excess of any ions in the intestine that cannot be absorbed draws more water into the colon, helping to mobilize the excess fecal matter that has solidified. A greater volume of feces in the colon stimulates it to move and expel this, and the water that the magnesium drags along with it helps the colon get rid of it.
The dosage and explanation are as follows:
- A smaller dose of milk of magnesia is prescribed for hyperacidity. About one gram of milk of magnesia will do the trick, but consult with your physician first. This is because this dose of milk of magnesia does not aim to fully neutralize the gastric acid levels, but mitigate them so that the stomach walls do not get damaged. The stomach must retain some level of acidity so that it can break down your food properly. Acidity is important in breaking down proteins into its smaller components, as well as activating some of your stomach’s enzymes. A lack of acidity leads to malnourishment and other problems.
- A larger dose of milk of magnesia is prescribed for constipation. Two to six grams of milk of magnesia will do the trick, but as stated before, consult with your physician first. This dose of milk of magnesia will still have the anti-hyperacidity effect on your stomach, but the increased dosage will allow the magnesium ions to have enough osmotic pressure to draw water to itself in the colon, allowing the mechanism for stool evacuation to be carried out.
In addition, milk of magnesia should not be used in cases where one’s potassium serum levels are low. The water that comes into the colon from its walls, not just from stimulation by milk of magnesia, comes with a lot of potassium. Potassium is necessary for muscle function, including the heart. If one is going to use milk of magnesia, ensure that one takes in the necessary potassium to counteract this loss. Of course, one should definitely not overdose on this drug.
In summary, milk of magnesia dosage should be regulated in a case to case basis. Do not take more or less than what is prescribed for the condition. It may be an over-the-counter drug in most cases but do ask for a physician’s advice because there may be an underlying problem. Indeed, “If symptoms persist, consult your doctor” holds true here.