Sports Research® Magnesium Oxide 420mg with Coconut MCT Oil - Magnesium Supplement for Muscle, Nerve, and Bone Support* - Gluten-Free, Non-GMO - 90 Softgels

Clinical trials typically use Magnesium: 310–420mg/day (RDA for adults); therapeutic research typically 300–400mg elemental/day. Sports Research Magnesium Oxide 420mg Softgels delivers 420mg magnesium oxide per softgel (≈100% DV), which we classify as Full relative to that range.

See the "Also consider" section below for two alternatives. Choose based on form preference (Softgel vs alternatives), dose adequacy, and third-party testing.

Yes — IGEN Non-GMO Tested, Gluten-Free, Third-Party Tested. Third-party testing verifies ingredient identity and label accuracy.

Yes — Amazon Subscribe & Save is available for this product. Enrolling locks in a recurring delivery at a reduced per-unit price.

Magnesium oxide can reduce the absorption of certain antibiotics (fluoroquinolones, tetracyclines), bisphosphonates, and some osteoporosis medications — separate doses by at least 2 hours. It may also enhance the effect of blood pressure medications and some diabetes drugs. Always inform your healthcare provider about magnesium supplementation, especially if on prescription medications.

Magnesium oxide at high doses (420mg+) can cause loose stools, cramping, or diarrhea due to its osmotic effect in the GI tract — this is the same mechanism that makes it effective as a laxative. Long-term use at this dose without monitoring can theoretically cause hypermagnesemia in individuals with kidney impairment. Those with kidney disease should consult their physician before using any magnesium supplement.

Yes — magnesium oxide has a well-documented laxative effect, particularly at 420mg doses, because its low absorption means a large amount reaches the colon. Some users experience loose stools or GI cramping, especially initially. Taking with food and adequate water minimizes this. If GI effects are problematic, Sports Research's Magnesium Glycinate SKU is absorbed earlier in the GI tract and is much less likely to cause digestive issues.

Magnesium combines well with vitamin D3 (required for magnesium metabolism), vitamin K2 (synergistic for bone health), and B vitamins. Avoid taking simultaneously with calcium, iron, or zinc supplements, as these minerals compete for absorption. The biolipid matrix in this formula is compatible with fat-soluble vitamins but space them out from other minerals.

Take one softgel daily with a full glass of water and a meal. Do not exceed one softgel per day without medical supervision. Individuals with kidney disease or compromised renal function should avoid magnesium supplementation without physician guidance. If you experience significant diarrhea or cramping, reduce to alternate-day dosing or switch to a higher-bioavailability form like magnesium glycinate.

Due to magnesium oxide's low bioavailability (~4%), systemic magnesium status changes slowly — expect 4–8 weeks before measurable improvements in serum or red blood cell magnesium levels. GI-specific effects (osmotic stool softening) can occur within hours of the first dose. For sleep or muscle relaxation benefits, a higher-bioavailability magnesium form will show effects much faster.