Magnesium Glycinate vs Citrate vs L-Threonate

By Futuro Labs Editorial Team · Reviewed by an independent UK-registered nutritionist · Published 10 May 2026

Magnesium glycinate, citrate, and L-threonate are the three forms most UK buyers compare — and they're not interchangeable. They have different absorption profiles, different evidence bases, and different ideal use cases. Picking the wrong form for your specific goal often produces underwhelming results not because magnesium 'doesn't work' but because the form doesn't match.

Magnesium glycinate, citrate, and L-threonate are the three forms most UK buyers compare when shopping for magnesium supplements — and they're not interchangeable. They have different absorption profiles, different evidence bases for different outcomes, and different ideal use cases. Picking the wrong form for your specific goal often produces underwhelming results not because magnesium "doesn't work" but because the form doesn't match the application.

This guide explains what each form actually does, when to choose which, and whether stacking multiple forms makes sense.

Our top picks reviewed

At-a-glance comparison

Magnesium glycinate — best general-purpose form

Magnesium chelated to glycine — an amino acid that improves absorption and tolerability. Approximately 14% elemental magnesium by weight. The most-tolerated supplemental form even at NHS reference doses (300mg+ elemental). Glycine itself has mild calming properties that complement magnesium's stress and sleep effects.

Best for: stress regulation, sleep quality, general supplementation, perimenopausal symptoms, brain fog, anxiety. The default form for most UK adults.

Daily dose: 200-400mg elemental magnesium

Timing: evening, 1-2 hours before bed

UK pricing tier: 25p-£1+ per day across UK brands

Magnesium citrate — best for occasional constipation

Magnesium bonded to citric acid. Higher bioavailability than oxide; comparable to glycinate. Approximately 16% elemental magnesium by weight. Has well-documented laxative effect at higher doses (600mg+ elemental) — useful for occasional constipation but produces loose stools at supplemental doses.

Best for: occasional constipation relief, lower-dose general supplementation, budget supplementation when laxative effect isn't a concern.

Daily dose: 200-300mg elemental for general supplementation; 600mg+ for laxative effect

Timing: with meals, anytime of day

UK pricing tier: 10-30p per day — typically cheaper than glycinate

Magnesium L-threonate — premium cognitive option

Magnesium bonded to L-threonic acid. Patented form (Magtein) developed at MIT specifically for cognitive support. Limited evidence base but suggestive — early research suggests better blood-brain-barrier penetration than other forms. Most expensive UK magnesium form.

Best for: cognitive support specifically, age-related cognitive concerns, premium cognitive supplement protocols.

Daily dose: 144-200mg elemental (Magtein label dosing — 1500-2000mg of L-threonate compound)

Timing: split AM/PM dose typically

UK pricing tier: £1-2+ per day — substantially more expensive than glycinate or citrate

Head-to-head comparison

Bioavailability

All three are well-absorbed. Glycinate and citrate are comparable; L-threonate has unique brain-penetration claim but smaller human evidence base. All three substantially outperform magnesium oxide (4-5% absorbed).

Tolerability at full dose

Glycinate is best-tolerated at NHS-reference doses (300-400mg elemental). Citrate produces loose stools above 400mg elemental. L-threonate is well-tolerated at its lower elemental dose.

Evidence base

Glycinate has the strongest accumulated evidence for sleep, stress, and general supplementation. Citrate has well-established laxative effect plus general supplementation evidence. L-threonate has emerging cognitive evidence — promising but less established than the older forms.

Cost per active milligram

Citrate cheapest, glycinate mid-tier (FL Magnesium ~33p/day at 300mg elemental is competitive), L-threonate most expensive at typical UK pricing.

Who should choose which

Choose glycinate if:

• You're targeting sleep quality, stress regulation, or general supplementation
• You want the most-tolerated form at full elemental dose
• You have perimenopausal symptoms, anxiety, or brain fog
• You're an athlete or chronically stressed adult

Choose citrate if:

• You have occasional constipation
• You want lower-cost supplementation and don't need the highest tolerability
• You're at lower elemental dose tier (200mg or below) where laxative effect isn't an issue

Choose L-threonate if:

• You specifically want cognitive support and premium pricing isn't a concern
• You're already optimising other cognitive supplements (lion's mane, omega-3) and want a magnesium form aligned with cognitive goals
• You have age-related cognitive concerns and want the form with brain-penetration claim

Stacking multiple forms

Some premium UK protocols stack glycinate (evening, sleep/stress) + L-threonate (morning, cognitive) for combined benefit. This works mechanistically but pushes total elemental magnesium toward the supplemental upper limit (400mg). Calculate combined elemental content carefully. For most UK adults, single-form glycinate at full dose tier is the more practical approach.

Frequently asked questions

Last updated: 10 May 2026. All content is provided for general information only and is not intended to substitute for professional medical advice. If you have any health concerns, consult your GP or a qualified healthcare professional. Futuro Labs is a registered UK supplement manufacturer (Futuro Lab Supplements Ltd, 71-75 Shelton Street, London WC2H 9JQ). Affiliate links to Amazon UK and our own store are clearly disclosed.