Loading
Loading
Magnesium is the fourth most abundant mineral in your body and is involved in 300+ enzymatic reactions. An estimated 50% of Americans do not meet the RDA. But the form matters enormously -- magnesium oxide absorbs at just 4%, while glycinate and threonate offer dramatically better bioavailability. We rank every form and product.
| Factor | Glycinate | L-Threonate | Citrate | Oxide |
|---|---|---|---|---|
| Bioavailability | High (~80%) | High (brain-specific) | Moderate (~30%) | Very Low (~4%) |
| Elemental Mg/Dose | 200mg typical | 144mg (low) | 150-200mg | 400mg (label) |
| Actually Absorbed | ~160mg | ~144mg (brain) | ~50-60mg | ~16mg |
| GI Side Effects | Minimal | Minimal | Moderate (loose stools) | High (osmotic laxative) |
| Best Use Case | Sleep, relaxation, deficiency | Cognitive function, memory | General supplementation | Not recommended |
| Evidence Strength | Strong | Promising (limited RCTs) | Strong | Strong (negative) |
| Crosses BBB? | Partial (glycine helps) | Yes (unique) | No | No |
| Cost/Month | $7-15 | $27-30 | $5-12 | $2-5 |
| Our Verdict | Best all-around | Brain-specific premium | Decent budget option | Avoid |
The glycine chelate has calming properties that synergize with magnesium's muscle-relaxing effects. Well-absorbed, minimal GI issues. Take 200-400mg elemental magnesium 45-60 minutes before bed.
The only form demonstrated to cross the blood-brain barrier and elevate brain magnesium levels. MIT research showed enhanced synaptic plasticity. Best for adults 50+ concerned about cognitive health.
Both are well-absorbed. Glycinate has fewer GI effects. Citrate is slightly cheaper. For general deficiency, either works. Target 200-400mg elemental magnesium daily.
Magnesium is required for muscle relaxation (calcium contracts, magnesium relaxes). Glycinate's superior absorption means more magnesium reaches muscle tissue. Athletes lose magnesium through sweat.
The osmotic effect that makes citrate and oxide poor for absorption makes them effective as gentle laxatives. If constipation is your primary concern, citrate at higher doses can help. But this is a side effect, not a supplement benefit.
Magnesium oxide is the most commonly sold form because it is the cheapest to manufacture and has the highest elemental magnesium content per pill (60% by weight). The label says 400mg. Sounds impressive.
But bioavailability studies consistently show only 4-5% absorption. That means your body actually absorbs approximately 16-20mg from that 400mg tablet. The rest passes through your gut as an osmotic laxative.
Compare that to magnesium glycinate at 200mg elemental with ~80% bioavailability -- you absorb roughly 160mg. That is 8-10x more magnesium actually entering your bloodstream from a lower label dose.
The cost difference? Glycinate costs $0.15-0.47/serving vs $0.05 for oxide. You pay 3-10x more but absorb 8-10x more. The math overwhelmingly favors glycinate. Magnesium oxide exists because consumers compare label doses, not absorbed doses.
Bottom line: If your magnesium supplement says "Magnesium Oxide" on the label, you are absorbing less magnesium than eating a handful of almonds.
| # | Product | Score | Verdict | Per Serving | Monthly | Form | Best For | |
|---|---|---|---|---|---|---|---|---|
| 1 | ThorneTop Pick Magnesium Bisglycinate | 88 | Best in Class | $0.47 | $14.10 | Glycinate | Sleep / Relaxation | Review |
| 2 | Life ExtensionBest for Brain Magnesium L-Threonate (Magtein) | 85 | Best in Class | $1.00 | $30.00 | L-Threonate | Brain / Cognitive | Review |
| 3 | NOW Foods Magnesium Glycinate | 83 | Worth Buying | $0.25 | $7.50 | Glycinate | Sleep / Relaxation | Review |
| 4 | Doctor's Best High Absorption Magnesium | 82 | Worth Buying | $0.18 | $5.40 | Glycinate | Sleep / Relaxation | Review |
| 5 | Life Extension Magnesium Caps | 81 | Worth Buying | $0.12 | $3.60 | Multi-Form Blend | General Deficiency | Review |
| 6 | Life Extension Magnesium L-Threonate (Magtein) | 80 | Worth Buying | $0.90 | $27.00 | L-Threonate | Brain / Cognitive | Review |
| 7 | Nature MadeBest Value Magnesium Oxide 400mg | 60 | Evidence Weak | $0.05 | $1.50 | Oxide | Laxative (poor absorption) | Review |
| 8 | Natural Vitality Calm Magnesium Gummies | 55 | Overhyped | $0.57 | $17.10 | Citrate | General / GI | Review |
NSF Certified for Sport chelated magnesium with excellent bioavailability. Thorne's bisglycinate delivers 200mg elemental magnesium per serving in a form that's gentle on the stomach, backed by strong absorption data, and produced under pharmaceutical-grade manufacturing standards.
The only magnesium form shown to cross the blood-brain barrier effectively. Strong evidence for cognitive function and sleep. Premium pricing reflects patented form.
The workhorse of magnesium supplements. Glycinate form is well-absorbed, gentle on the stomach, and NOW delivers it at an unbeatable price. No glamour, just function.
Magnesium glycinate/lysinate chelate with excellent absorption. 200mg elemental magnesium per serving at a budget-friendly price. Albion Minerals chelate is a respected source.
Three forms of magnesium (citrate, oxide, succinate) in one capsule for broad coverage. 500mg elemental magnesium at $0.12/serving. Life Extension's research-focused approach delivers value.
The only magnesium form demonstrated to cross the blood-brain barrier and elevate brain magnesium levels. Promising for cognitive function, but the evidence is still early-stage and it is expensive for the elemental magnesium you actually get.
The cheapest option, but you get what you pay for. Magnesium oxide has the worst bioavailability of any common form -- only 4% is absorbed. The 400mg label dose is misleading.
The gummy format is appealing but delivers only 83mg magnesium citrate per serving -- well below therapeutic doses. You would need 5 servings to match a single capsule of NOW Glycinate. Form over function.
Thorne Magnesium Bisglycinate (score: 88) ranks highest for its combination of NSF certification, excellent bioavailability, and pharmaceutical-grade manufacturing. For budget buyers, NOW Foods Magnesium Glycinate delivers comparable absorption at half the price. For cognitive-specific benefits, Life Extension Magtein is the only option with brain-penetrating evidence.
Glycinate wins for most use cases. It has higher bioavailability (~80% vs ~30% for citrate), significantly fewer GI side effects (no loose stools), and the glycine chelate adds calming properties beneficial for sleep. Citrate is acceptable as a budget option for general deficiency, but glycinate is the superior form for sleep, relaxation, and those with sensitive stomachs.
The RDA is 400-420mg for men and 310-320mg for women. Most people get 250-300mg from diet, so supplementing 200mg of a well-absorbed form (glycinate, threonate) covers the gap. Do not exceed 350mg from supplements alone (the UL for supplemental magnesium). Magnesium from food has no upper limit concern.
Excess supplemental magnesium primarily causes GI distress (diarrhea, cramping) -- this is the body's natural regulation mechanism. The tolerable upper limit for supplemental magnesium is 350mg/day. Severe hypermagnesemia from oral supplements is extremely rare in people with normal kidney function. Those with kidney disease should consult their physician before supplementing.
For sleep: 45-60 minutes before bed. For general supplementation: any consistent time works. Magnesium can be taken with or without food -- glycinate absorbs well either way. Avoid taking magnesium simultaneously with zinc, calcium, or iron, as they compete for absorption. Space mineral supplements at least 2 hours apart.
We rank supplements across 15+ categories using the same evidence-first methodology. No sponsorships, no affiliate bias -- just science.