Minerals
Magnesium Oxide — timing, dose & interactions
Packs the most magnesium into one pill but is poorly absorbed — about 4% in one study, against much higher, similar absorption for chloride, lactate and aspartate. Mainly useful as a laxative or antacid rather than to raise magnesium levels.
Timing
When to take it
Take with food; it works partly as an antacid and laxative.
Dose note. UL applies to all supplemental magnesium combined (not food); mainly to prevent diarrhea.
Interactions
Magnesium Oxide with other supplements
Magnesium Oxide + Calcium
Very high calcium may reduce magnesium absorption
Magnesium Oxide + Zinc
Very high zinc can reduce magnesium absorption
Magnesium Oxide + Vitamin D3
Magnesium is required to activate vitamin D
Magnesium Oxide + Psyllium Husk
Fiber can reduce magnesium absorption
Magnesium Oxide + Potassium
Low magnesium makes low potassium hard to fix
Magnesium Oxide + Magnesium
Two forms of magnesium
Magnesium Oxide + Magnesium Glycinate
Two forms of magnesium
Magnesium Oxide + Magnesium Citrate
Two forms of magnesium
Magnesium Oxide + Magnesium L-Threonate
Two forms of magnesium
Magnesium Oxide + Magnesium Malate
Two forms of magnesium
Safety
Medications & health conditions
Magnesium reduces levothyroxine absorption. Magnesium binds levothyroxine in the gut and can lower thyroid hormone levels. Keep it at least 4 hours away from your thyroid medication.
Magnesium blocks absorption of these antibiotics. Magnesium binds tetracycline and quinolone antibiotics in the gut, which can make the antibiotic less effective. Typically take the antibiotic at least 2 hours before or 4–6 hours after magnesium — the exact spacing depends on the drug, so follow its label.
Magnesium can build up with kidney disease. The kidneys remove excess magnesium. With reduced kidney function, supplements can cause dangerous hypermagnesemia.
PPIs can lower magnesium. Long-term PPI use is linked to low blood magnesium. That's a reason to have your level checked, not a reason to avoid magnesium.
Magnesium blocks HIV integrase inhibitors. The labels advise taking dolutegravir or bictegravir 2 hours before or 6 hours after products containing magnesium.
Buying guide
What to look for on the label
Magnesium Oxide
- Choose citrate or glycinate instead if absorption is the goal
FAQ
Common questions
When is the best time to take Magnesium Oxide?
Dinner. Take with food; it works partly as an antacid and laxative.
Should Magnesium Oxide be taken with food?
Yes. Taking it with a meal reduces stomach upset.
Can you take Magnesium Oxide with Calcium?
Yes, at normal doses. At high calcium doses, spacing them out is a reasonable precaution. No action needed at typical doses. If you take ≥1,000 mg calcium from supplements, take magnesium at a different time (e.g. bedtime).
Can you take Magnesium Oxide with Zinc?
Yes — this only matters at very high zinc doses. Keep zinc within the 40 mg/day upper limit.
Can you take Magnesium Oxide with Vitamin D3?
Yes — adequate magnesium helps vitamin D work, especially at higher D doses. Make sure magnesium intake is adequate if you take vitamin D, especially at higher doses. They do not need to be taken at the same time.
Can you take Magnesium Oxide with Psyllium Husk?
Separate them by about 2 hours. Take psyllium at least 2 hours apart from magnesium.
Sources