Magnesium glycinate vs citrate vs L-threonate — which form is right for you?
All three are real magnesium and all three will move your blood and tissue magnesium up if you're deficient. They differ on the parts of that statement most buyers actually care about: how fast it gets in, how kindly your gut tolerates it, and whether the chosen anion (glycine, citric acid, threonic acid) does anything useful in its own right.
Quick verdict
| Goal | Best-fit form | Why |
|---|---|---|
| Sleep, anxiety, restless legs | Glycinate | Gentle on gut at higher doses; glycine itself is a calming co-agonist at NMDA-related receptors and shows weak independent sleep-onset benefit. |
| Constipation, mild laxative effect wanted | Citrate | Faster onset, draws water into the bowel — sometimes a feature, sometimes a side-effect. |
| Cognitive endpoints (memory, focus, age-related cognition) | L-threonate (Magtein) | The only form with positive cognitive-endpoint RCTs. Premium price; not the form to start with for general repletion. |
| Generic daily repletion, lowest cost per gram | Citrate or oxide | Citrate has reasonable bioavailability at low cost. Oxide is cheapest but absorbs poorly — fine if you take enough of it, less efficient. |
How they compare on the things that matter
Bioavailability — how much actually gets in
Direct head-to-head pharmacokinetic studies are limited and use small samples, but the relative ordering is consistent. Organic chelates (glycinate, citrate, malate, taurate) outperform inorganic salts (oxide, sulphate) on serum magnesium AUC by roughly 15–40%. Among the organic forms, the differences are smaller than the marketing implies — most studies find glycinate and citrate within 10% of each other.
L-threonate is a special case. Per gram of elemental magnesium, its serum bioavailability is similar to other organic forms. Its distinguishing claim is brain-tissue uptake — animal data show higher CSF and hippocampal magnesium with L-threonate than with comparable doses of other forms. Whether that translates to humans at supplemented doses is the open question; the small RCTs to date are encouraging but not definitive.
GI tolerance — the practical limit on dose
This is usually the deciding factor for people taking 300+ mg/day. Citrate and oxide both pull water osmotically into the small intestine and can cause loose stools or cramping at higher doses. Glycinate is the most reliably gentle — most users tolerate 400 mg elemental magnesium without GI upset. L-threonate is also well-tolerated but is rarely taken at high elemental-magnesium doses (most products deliver ~140 mg per serving).
Evidence base by clinical endpoint
- Sleep onset / sleep quality: Strongest evidence for glycinate (small RCTs in older adults). Citrate has indirect support. L-threonate has no sleep-specific RCTs.
- Anxiety / stress: Glycinate and taurate forms most studied; effect sizes modest, mostly in subjects with low baseline magnesium.
- Migraine prevention: Most positive trials used citrate at 600 mg elemental magnesium. The American Headache Society includes magnesium in its prevention guidelines.
- Cognitive function: L-threonate is the only form with positive human cognitive RCTs (modest improvements in working memory and attention in older adults). Replication is limited.
- Glycaemic control / insulin sensitivity: No clear advantage for any specific form. All forms work similarly when baseline magnesium is low.
- Bone density: Cumulative intake matters more than form. Most osteoporosis-relevant trials used citrate or oxide.
What the price difference buys you
Per gram of elemental magnesium, the cost ladder runs roughly: oxide (cheapest) → citrate → malate → glycinate → taurate → L-threonate (most expensive, often 5–8× citrate). The premium for L-threonate is real because the licensed Magtein extract has actual clinical data behind it — but only pay it if cognitive endpoints are your specific goal. For sleep, stress, or muscle cramps, the cheaper glycinate is the better-evidenced choice.
Who should not take any of these
People with significant kidney disease (eGFR < 30) should not supplement magnesium without nephrology supervision — the kidneys clear magnesium, and impaired clearance can produce dangerous hypermagnesemia. People on bisphosphonates, tetracyclines, or quinolone antibiotics should separate magnesium dosing by 2 hours to avoid chelation interference. Pregnancy is generally fine at standard doses, but high-dose oral magnesium (often used as a pre-eclampsia adjunct) should be physician-managed.
What we'd actually buy
For the median person — sleep support, mild deficiency repletion, generally well-tolerated form: a 200–400 mg elemental glycinate, taken with the evening meal. For active migraine prophylaxis: 600 mg elemental citrate, divided across the day. For specifically cognitive endpoints in adults over 50: a Magtein-licensed L-threonate at the trial-validated 1.5–2 g/day total compound (delivering roughly 144 mg elemental magnesium per serving).
None of these recommendations are sponsored. Verified-tested brand options are listed on each supplement's individual page (look for the "Verified brands" panel).