From the Research
Magnesium oxide typically begins to take effect within 3-6 hours after ingestion of a 500mg dose. This timeframe can vary between individuals based on factors such as stomach acidity, food intake, and individual metabolism. The onset is relatively slow compared to other magnesium formulations because magnesium oxide has lower bioavailability (only about 4-5% is absorbed) 1. When taken for constipation, you may notice effects within a few hours, while for magnesium supplementation to address deficiency, it may take regular daily dosing over several days to weeks to notice improvements in symptoms.
Some key points to consider when taking magnesium oxide include:
- Taking magnesium oxide with food can help reduce potential gastrointestinal side effects like diarrhea or stomach cramps, though this may slightly delay absorption 2.
- For optimal absorption, it's best to divide the 500mg into smaller doses throughout the day rather than taking it all at once, and staying well-hydrated will help both with absorption and reducing side effects 3.
- The use of magnesium oxide should take account of the most appropriate dose, the serum concentration, drug-drug interactions, and the potential for side effects, especially in the elderly and in patients with renal impairment 1.
- Emerging clinical evidence indicates that the use of magnesium oxide is convenient to administer, of low cost, and safe, but its prescription has largely been based on empirical knowledge 1.
It's also worth noting that reducing the number of daily doses of MgO does not affect its laxative action, as shown in a single-center retrospective study 3. Additionally, a study on the effects of magnesium citrate, magnesium oxide, and magnesium sulfate supplementation on arterial stiffness in healthy overweight individuals found that magnesium citrate supplementation results in a clinically relevant improvement of arterial stiffness, but the effects of magnesium oxide were not significant 4. Another study found that magnesium oxide does not enhance the recovery of gastrointestinal function within the context of an evidence-based multimodal rehabilitation programme after open colonic surgery 5.