**Magnesium** at 250mg per tablet lands within the clinical supplemental range of 100–400mg — but the form is magnesium oxide, which has roughly 4% absorption. That means your body is likely taking in only about 10mg of usable magnesium from each serving, well below what you'd need for meaningful support with sleep, stress, or muscle recovery.

The tablet also includes 65mg of **Calcium** as calcium carbonate, but that's a fraction of the 200–600mg supplemental range and won't move the needle for bone support. There are no complementary nutrients like vitamin D or K2 to enhance absorption of either mineral.

If you're supplementing magnesium for a specific health goal, the oxide form is the biggest limitation here. You'd absorb substantially more from a glycinate, citrate, or threonate form at the same dose — and those forms are also gentler on the stomach.

BioStacks
21st Century

Magnesium 250 mg

1 Tablet · 110 servings · $0.05/serving

iHerbAmazon

Best for

Heart

Ingredients (2)

Magnesium

100%

Dose

250 mg

Target

100–400 mg

Form

Budget

Calcium

65 mg

Trace amount — not scored

Other Ingredients (4)

KelpFood

Dried brown seaweed used as a whole-food source of iodine and trace minerals.

Microcrystalline CelluloseBinder

Plant-derived cellulose used as a binder and filler in supplements

Croscarmellose SodiumDisintegrant

Cross-linked cellulose derivative used as a superdisintegrant

Stearic AcidLubricant

Saturated fatty acid used as tablet lubricant

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Sources & Scoring

Nutrient data (RDA, UL, and safety thresholds) sourced from: NIH Office of Dietary Supplements and National Academies Dietary Reference Intakes (DRI).

This is not medical advice. Consult a healthcare provider before making changes to your supplement routine.

The score analyzes what's on the label: ingredient doses vs. clinical ranges, chemical forms, evidence levels, and known interactions. It does not verify label accuracy or test for contaminants — for that, look for third-party certifications like USP or NSF.

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