Magnesium Glycinate vs Oxide: Absorption, Side Effects and Cost
Magnesium oxide contains a lot of magnesium per pill but is poorly absorbed, so much of it stays in the gut and draws in water. That makes it effective for constipation and heartburn but a poor choice for raising your magnesium levels. Magnesium glycinate is absorbed better and is gentle on the stomach, making it the better pick for daily supplementing.
Magnesium glycinate vs oxide is really a question of what you want magnesium to do. Magnesium oxide is in many multivitamins and cheap tablets. Magnesium glycinate costs more. Is it worth it? It depends on why you're taking magnesium.
Side-by-side
| Magnesium glycinate | Magnesium oxide | |
|---|---|---|
| Elemental magnesium by weight | About 14% | About 60% |
| Absorption | Good | Poor |
| Laxative effect | Minimal | Strong at higher doses |
| Main use | Raising magnesium intake | Constipation, heartburn |
| Cost | Higher | Very low |
Why oxide absorbs poorly
Oxide is an inorganic salt that doesn't dissolve well in the gut. Studies comparing forms, including a randomized trial, found organic forms such as citrate raised blood and urine magnesium more than oxide. The magnesium that isn't absorbed pulls water into the intestine, which is why oxide works as a laxative.
When oxide makes sense
- Occasional constipation
- Heartburn relief as an antacid
- A very low budget, accepting that less is absorbed
When glycinate makes sense
- Daily supplementing to close a dietary gap
- Sensitive stomach
- Evening use without bathroom trips
Dosing and safety
Supplemental magnesium of any form should stay at or below 350 mg a day unless your doctor advises more. Separate magnesium from some antibiotics, bisphosphonates and thyroid medication. See the best time to take magnesium.
The verdict
Choose glycinate if you want to raise your magnesium. Choose oxide only if constipation relief is the goal. For another comparison, read magnesium glycinate vs citrate.
Frequently asked questions
Why is magnesium oxide so common in multivitamins?
It's cheap and compact: it contains more magnesium by weight than other forms, so it fits in a small tablet.
Is magnesium oxide bad for you?
No, but higher doses often cause diarrhea, and people with kidney disease should avoid unsupervised use.
Sources
This page is for education and is not a substitute for advice from your doctor. Read our medical disclaimer.