Magnesium Glycinate vs Citrate vs Oxide (Pharmacist Guide)

Glycinate for sleep. Citrate for digestion. Oxide for almost nothing useful.

That is the 30-second answer to "magnesium glycinate vs citrate vs oxide", and it is the one most supplement labels obscure. A 500 mg magnesium oxide capsule delivers about 10 mg of absorbed magnesium because oxide is roughly 4% bioavailable in healthy adults (Firoz & Graber, 2001). A 500 mg magnesium glycinate capsule delivers around 55 mg absorbed because the chelate moves through a different intestinal pathway entirely (Schuette et al., 1994). The form on the bottle decides whether you got a supplement or a laxative. Below is the pharmacist version of how to pick the right one, what halal status each major brand carries, where Canadian readers can buy them, and a personal testing methodology I have run through with five glycinate brands.

Why trust this review

I am Kazi Habib, B.Pharm, MBA, PMP, with 10+ years across pharmaceutical sciences and life-sciences marketing, and I run FitFixLife and PharmoniQ. The picks below come from cross-referencing Health Canada NPN licensing, NSF and Informed Sport public databases, and Certificates of Analysis I requested directly from manufacturers, plus the personal N-of-1 sleep testing methodology I describe later in this article.

Why magnesium form matters more than dose

Magnesium does not exist as a free element you can put in a capsule. It always shows up bonded to something else, and that "something else" decides three things at once: how much of the capsule weight is actually magnesium, how much your gut absorbs, and what side effects the partner molecule brings along.

Start with the label math. A bottle that says "Magnesium 400 mg" almost never means 400 mg of usable magnesium. It usually means 400 mg of compound, of which only a fraction is elemental magnesium, the part your cells actually use. Magnesium oxide is 60% elemental by weight, so a 400 mg oxide capsule contains 240 mg of elemental Mg on paper. Magnesium glycinate is around 14% elemental, so a 400 mg glycinate capsule contains around 56 mg elemental on paper. Oxide looks twice as good as glycinate at this stage. Most labels stop here.

The second step is bioavailability: of the elemental magnesium that the compound contains, how much actually crosses your intestinal wall? Firoz and Graber's 2001 study in Magnesium Research measured urinary magnesium excretion in healthy volunteers and found magnesium oxide had a fractional absorption of about 4%, while chloride, lactate, and aspartate all absorbed substantially better. The mechanism is simple: oxide is poorly soluble in water and resists the low-pH dissolution gastric chemistry that organic salts undergo.

Multiply elemental percent by bioavailability and you get the real number. The 400 mg oxide capsule with 240 mg elemental at 4% absorption delivers around 10 mg into circulation. The 400 mg glycinate capsule with 56 mg elemental at roughly 23-30% absorption delivers around 14-17 mg, and possibly more because some glycinate is absorbed intact as a dipeptide through a second transport pathway (Schuette et al., 1994). The "cheaper" oxide product is delivering less magnesium per capsule, not more.

This is the kind of math my pharmacy education trained me to flag immediately, and it is the kind of math supplement labels are designed to hide. When a bottle advertises a big magnesium number and a small price, look at the form before you look at anything else.

Magnesium glycinate (bisglycinate): best for sleep and anxiety

Magnesium glycinate, often labeled bisglycinate to indicate two glycine molecules per magnesium ion, is a true amino-acid chelate. The chelation matters because it changes how the compound moves through your gut. Schuette and colleagues (1994), publishing in JPEN Journal of Parenteral and Enteral Nutrition (PMID 7815675), gave 100 mg doses of magnesium diglycinate and magnesium oxide to 12 patients with ileal resections in a double-blind crossover. In patients with the most severely impaired absorption, diglycinate delivered 23.5% fractional absorption versus 11.8% for oxide. The authors concluded "some portion of magnesium diglycinate is absorbed intact, probably via a dipeptide transport pathway", which is the chelate's actual mechanistic advantage. In healthy adults the difference is smaller, but the directional finding is consistent across the literature: glycinate gets in, oxide largely does not.

The carrier is the second half of the value. Glycine is an inhibitory neurotransmitter in the central nervous system and a substrate for serotonin synthesis. Bannai and Kawai (2012) reviewed the clinical sleep work on glycine in the Journal of Pharmacological Sciences (PMID 22293292) and concluded that "glycine ingestion before bedtime significantly ameliorated subjective sleep quality in individuals with insomniac tendencies", with the proposed mechanism being a small drop in core body temperature, which is itself a sleep-onset signal. So a glycinate capsule before bed gives you two effects in one dose: the magnesium component (which has its own sleep evidence; see citrate section below for the Abbasi RCT context) and the glycine component, which improves sleep on its own.

The third advantage is GI tolerability. Glycinate does not pull large amounts of water into the intestinal lumen the way poorly absorbed magnesium salts do, so loose stool is rare even at 400-500 mg elemental doses. In my own use across roughly two years of nightly glycinate (200-400 mg elemental), I have had loose stool exactly twice, both times after pairing it with a high-magnesium dinner. By contrast, the same dose as citrate puts me on a four-hour bathroom clock.

Brands worth considering. Thorne Magnesium Bisglycinate carries NSF Certified for Sport, which is the strictest third-party testing program for athletes because it screens for banned substances batch-by-batch. CanPrev Magnesium Bis-Glycinate 200 is the Canadian standard and uses a vegetable capsule with a Health Canada NPN, which matters for halal-friendliness (more on that below). Pure Encapsulations Magnesium Glycinate is a clean-label option that ConsumerLab has tested favorably in past reports.

Magnesium citrate: best for digestion, weakest for sleep

Citrate is magnesium bound to citric acid, which is the same molecule that makes lemon juice sour. It dissolves well in water, which gives it two consequences: better absorption than oxide, and a pronounced osmotic effect in the gut at the doses people actually use.

On absorption, Walker and colleagues (2003) ran a 60-day randomized double-blind trial with 46 healthy participants comparing magnesium oxide, citrate, and amino-acid chelate at 300 mg elemental daily, published in Magnesium Research (PMID 14596323). The organic forms (citrate and chelate) both outperformed oxide. Citrate produced the greatest mean serum magnesium concentration after both acute (P = 0.026) and chronic (P = 0.006) supplementation. That is real-world evidence that citrate moves magnesium into circulation; the typical estimate of around 25-30% fractional absorption is consistent with this finding.

The osmotic effect is where citrate stops being a general-purpose supplement and starts being a targeted tool. Magnesium ions that are not absorbed in the small intestine carry water with them into the colon, which softens stool and stimulates bowel movement. At 300 mg elemental citrate, most people notice a mild softening. At 500 mg, many notice an urgent bowel movement within 2-4 hours. At 1,500 mg, you get the full colonoscopy-prep dose: the same magnesium citrate solution pharmacies stock as Citroma is what most colonoscopy patients drink the night before their procedure (PMID 35211711 discusses its adequacy in this role). This is not theoretical. Magnesium citrate is in the actual hospital formulary because it works as a laxative.

For supplementation purposes, this gives citrate two clean use cases. First, constipation or IBS-C, where the osmotic effect is the feature, not the bug; 200-300 mg elemental at night usually produces a comfortable morning bowel movement without the urgency of stimulant laxatives. Second, post-travel bowel reset, where dehydration and time-zone-shifted eating have stalled the GI tract; 300 mg elemental for two or three nights resolves most flight-induced constipation in adults.

Where citrate falls short is sleep. The Abbasi 2012 insomnia trial that everyone cites for "magnesium helps sleep" actually used magnesium oxide, not citrate (more on that in the next section), and the cleanest glycine-sleep evidence is from glycinate, not citrate. For people taking magnesium specifically to fall asleep faster, citrate at sleep-effective doses (300 mg+) hits a fork: too low to produce a strong magnesium effect, but high enough to trigger an inconvenient 2 AM bathroom visit. This is why my pharmacy textbook framing of citrate is "supplement that doubles as a mild laxative", not "sleep supplement that occasionally upsets the stomach".

Natural Vitality Calm deserves a specific note because it is genuinely the most-sold magnesium product in North America. It is magnesium citrate generated by reacting magnesium carbonate with citric acid in water, which is also why it fizzes. The dose per scoop runs around 325 mg elemental at the standard serving, which is exactly in the laxative-effect zone for most adults. People who love it usually love it for the gut-regularity effect; people who hate it usually drank a full scoop the first time and learned what 325 mg of citrate does to a normal bowel.

Magnesium oxide: cheap but 4% bioavailable

Magnesium oxide is the form that exposes the entire supplement industry's incentive structure. It is 60% elemental magnesium by weight, which is the highest of any common form. It is also one of the cheapest active ingredients in supplement manufacturing, often pennies per dose. Those two facts together explain why oxide is in 60% of drugstore multivitamins and most house-brand "magnesium" bottles: the label can claim a big magnesium number, and the manufacturer can hit it for almost nothing.

The fractional absorption data, however, is unforgiving. Firoz and Graber (2001), publishing in Magnesium Research (PMID 11794633), measured urinary magnesium excretion across four commercial preparations in healthy volunteers and reported magnesium oxide at "fractional absorption 4 per cent", while magnesium chloride, lactate, and aspartate all performed several-fold better. The mechanism is solubility: oxide is poorly soluble at gastric pH, transit time is too short for full dissolution in most adults, and the unabsorbed fraction passes into the colon where it pulls water in osmotically. The 60% elemental advertising number, multiplied by the 4% absorption number, is the actual delivered dose: a 400 mg oxide capsule provides somewhere around 10 mg of absorbed magnesium per dose.

The Walker 2003 trial confirms the same direction. After 60 days of 300 mg elemental daily, oxide showed no statistically significant serum magnesium change versus placebo, while citrate and chelate both did (PMID 14596323). That is the cleanest experimental disproof you will find for "magnesium oxide as a meaningful supplement". For two months, three times daily, oxide is indistinguishable from a sugar pill on the metric you care about.

So why does it exist? Two legitimate uses. First, acute constipation, where you actually want the osmotic effect of 230 mg of unabsorbed magnesium reaching the colon; 400-800 mg oxide is a textbook stool softener, and at that dose-effect mismatch it works because the laxative effect does not require absorption. Second, antacid use, where the oxide reacts with stomach acid to form magnesium chloride and water, neutralizing acid the way Mylanta or Maalox does (those products are partly magnesium hydroxide, a cousin chemistry).

Elemental magnesium per dose: the metric most labels hide

The single most useful exercise when picking a magnesium product is the elemental-per-absorbed calculation. Most labels make you do it manually because the Supplement Facts panel usually lists only "Magnesium (as [form]) Xmg, Y% DV", which is the elemental portion, but not the bioavailability. Here is the cheat sheet I keep mental notes on for the five forms I actually consider:

Two notes on this table. First, "bioavailability" in the magnesium literature is measured several ways (urinary excretion, serum AUC, retention balance), and the numbers vary across methods, which is why I show ranges rather than precise percentages. Second, the chelate column is the most contested, because Schuette's healthy-adult data shows glycinate and oxide nearly tied (~23%), while the impaired-absorption subgroup and the Walker 2003 chelate arm both favor glycinate, and the dipeptide-pathway absorption Schuette describes adds an absorption route oxide cannot use. The defensible summary is that glycinate is at least as well-absorbed as citrate in healthy adults and substantially better in compromised gut function.

For practical purposes, the cost-per-absorbed-milligram order is roughly: glycinate is comparable to malate, then citrate, then oxide far behind. L-threonate is in its own category because the value is brain-targeted delivery, not total systemic absorption; you pay a premium for that. Multivitamin formulations that list "Magnesium (as magnesium oxide and magnesium citrate)" without a per-form breakdown are usually 80%+ oxide by mass, because that is how you hit a high label number for low manufacturing cost.

Side effects, contraindications, drug interactions

Magnesium is one of the safest supplements at recommended doses. The Institute of Medicine sets the tolerable upper intake level for supplemental magnesium (the part you add on top of food) at 350 mg elemental per day for adults, specifically because higher supplemental doses raise the risk of GI side effects, not toxicity. Most adults can tolerate 400 mg elemental glycinate cleanly; many tolerate 600-800 mg citrate but at that range the laxative effect dominates.

GI side effects by form. Oxide and citrate produce loose stool most often because the unabsorbed fraction draws water into the colon; oxide at 400 mg often causes a bowel movement within 2-6 hours in adults with normal motility. Glycinate produces loose stool rarely, typically only above 600 mg elemental. Malate and taurate sit between glycinate and citrate on the tolerability axis.

Kidney disease is the one absolute caution. Magnesium is excreted by the kidneys, and people with reduced kidney function (eGFR <30 mL/min/1.73m², or anyone on dialysis) can accumulate magnesium to dangerous levels even at "normal" supplement doses. Symptoms of hypermagnesemia include facial flushing, nausea, low blood pressure, and at extreme levels cardiac conduction problems. Anyone with significant chronic kidney disease should not take magnesium supplements without their nephrologist's input.

Drug interactions worth knowing

• Proton pump inhibitors (omeprazole, pantoprazole, esomeprazole, lansoprazole). Chronic PPI use is associated with hypomagnesemia. William and Danziger reviewed the evidence in the Journal of Clinical Pharmacology in 2016 (PMID 26582556), summarizing that "a large body of observational data has linked chronic PPI use with hypomagnesemia" via decreased intestinal absorption. The FDA issued a Drug Safety Communication on this in 2011, which is why your prescriber should be checking magnesium periodically if you have been on a PPI for more than a year. Practical implication: PPI users often need glycinate supplementation specifically (not oxide; oxide absorption depends partly on gastric acidity, which PPIs suppress).
• Tetracyclines and fluoroquinolone antibiotics (doxycycline, ciprofloxacin, levofloxacin). Magnesium binds these drugs in the gut and reduces their absorption. Space dosing by at least 2 hours, preferably 4. This is in every Drug Information handbook.
• Bisphosphonates (alendronate, risedronate, zoledronic acid). Same chelation problem. Take bisphosphonates first thing in the morning on empty stomach, then wait 30-60 minutes before magnesium.
• Loop diuretics (furosemide, bumetanide, torsemide) increase magnesium excretion, so chronic users often run low on magnesium and benefit from supplementation. Potassium-sparing diuretics (spironolactone, amiloride) do the opposite and modestly reduce magnesium loss.
• Levothyroxine (Synthroid, Eltroxin). Less well-known, but magnesium can reduce thyroid hormone absorption if taken within 4 hours. Take levothyroxine first thing AM, magnesium at night, never together.

Halal certification status of major magnesium brands

This is the section the rest of the internet skips, which is a missed value for the roughly 1.9 billion Muslim consumers globally and a growing audience in North America. Magnesium itself is a mineral, so the mineral content is halal regardless of brand. The questions are about the capsule shell (gelatin vs vegetable), the excipients (especially magnesium stearate's animal-vs-vegetable origin), and any flow agents that may use ethanol carriers.

The 5 internationally-recognized halal certifying bodies are JAKIM (Malaysia), MUI (Indonesia), IFANCA (US), HFA (UK), and ESMA (UAE). A product carrying a mark from any one of these has been audited against a documented standard. A product without one of these marks is not necessarily non-halal; it is just not third-party verified. "Halal-friendly", "suitable for vegetarians", or "vegan capsule" formulations are usually safe defaults when no certifier mark is present.

Capsule shell. Gelatin capsules without certification can be bovine (often halal-friendly) or porcine (not halal). Most premium supplement brands now use HPMC (hydroxypropyl methylcellulose), a plant-derived capsule that is halal-acceptable by default. The label terms to look for are "vegetable capsule", "vegetarian capsule", "veggie cap", "plant-based capsule", or "HPMC".

Magnesium stearate. This is the most common flow agent in capsule manufacturing and the most common halal question I get. It can be derived from animal fat (tallow) or vegetable sources (palm, coconut). The product label rarely specifies. For halal-strict consumers, default to brands that explicitly state "vegetable-source magnesium stearate" or use rice flour or silica as alternative flow agents. Some scholars consider magnesium stearate halal even from animal sources because the chemical transformation is complete; others do not. This is a fiqh question, not a chemistry one.

Brand-by-brand assessment for North American buyers

• Thorne Magnesium Bisglycinate. No formal halal certification. Uses HPMC vegetarian capsule, vegetable-source magnesium stearate per their published documentation. NSF Certified for Sport, which is the strictest US third-party purity standard. Halal-friendly default for most readers; not certified for halal-strict consumers.
• CanPrev Magnesium Bis-Glycinate 200 (Canada). No formal halal certification, but uses vegetable capsules and is licensed by Health Canada under NPN 80049366 (verify on Health Canada's Licensed Natural Health Products Database). Halal-friendly default; Canadian-formulated.
• Pure Encapsulations Magnesium Glycinate. Vegetarian capsules, ingredient list publicly disclosed, no allergens. Halal-friendly default; not formally certified.
• NOW Foods. NOW carries a mix of formulations; some specific SKUs are halal-certified by IFANCA (verify on the IFANCA certified products list before assuming). Their basic magnesium glycinate is in a vegetable capsule and halal-friendly by default.
• Lorna Vanderhaeghe Magsmart (Canada). Vegetable capsule, Canadian-made. No formal halal certification but ingredient-transparent and a common pick for halal-friendly Canadian consumers.
• Generic drugstore "Mag Oxide" bottles (Equate, Kirkland, Jamieson). Usually gelatin capsule, source unspecified. If halal certification matters to you, default to one of the brands above.

The pattern is simple: brands that use vegetable capsules and publish their ingredient sources are halal-friendly even without formal certification. Brands that use generic gelatin and refuse to specify the source are the ones to skip if halal status is non-negotiable.

Canadian magnesium market: what is actually available

The Canadian supplement market operates under a different regulatory frame than the US, which changes which brands are easy to find, what their labels look like, and what they cost.

Health Canada NPN. Every supplement sold in Canada must have a Natural Product Number (NPN) on the label, which is Health Canada's licensing identifier. NPN is a notification-plus-review system; it is more rigorous than FDA's "structure-function claim with no pre-market review" framework, but lighter than drug approval. An NPN means Health Canada reviewed the formula for known safety risks and accepted the manufacturer's claims, not that the bottle has been independently tested. Lookup is free at the Licensed Natural Health Products Database (search "magnesium bisglycinate" and the brand name to see the licensed claims).

Where Canadians actually buy magnesium

• iHerb Canada. Best selection for US and international brands (Thorne, Pure Encapsulations, Doctor's Best, NOW). Same products as US iHerb, with Canadian customs handling. Most pricing is competitive once converted; some products have GST/HST added at checkout.
• Costco Canada. Carries Kirkland Signature Magnesium (usually citrate or oxide blend depending on the SKU) at the best per-mg cost in the country. The trade-off is form: if the Kirkland bottle is oxide-heavy, the cost-per-absorbed-mg disappears. Read the Supplement Facts panel, not the front label.
• Amazon Canada. Wide selection; verify seller is the brand or an authorized reseller, not a gray-market reseller, especially for premium brands. Counterfeits are rare but not zero.
• Bulk Barn. Carries a few magnesium SKUs in their supplement aisle, usually lower-end brands. Useful for one-off purchases, not for ongoing supplementation.
• Shoppers Drug Mart / Rexall / London Drugs. Carry Canadian-made brands (CanPrev, Sisu, Webber Naturals, Jamieson) plus house brands. Quality varies by SKU; CanPrev and Sisu are the most reliable.

Canadian-made brands worth knowing

• CanPrev is the Canadian standard for bisglycinate; widely available, NPN-licensed, vegetable capsules.
• Sisu carries a comparable bisglycinate line, also NPN-licensed.
• Lorna Vanderhaeghe carries Magsmart and a few other magnesium formulations targeted at women's hormonal health.
• Jamieson carries the budget-tier options; usually citrate or oxide-citrate blends. Acceptable for general use, not ideal for sleep-specific supplementation.

The cost-per-effective-dose ordering in Canada usually goes: Costco Kirkland (best cost), Amazon-Canada NOW, Amazon-Canada CanPrev, iHerb Thorne (most premium). Premium-brand pricing in Canada runs roughly 25-40% higher than US pricing on a USD-equivalent basis, mostly because of distribution overhead and a smaller domestic market for premium supplements.

I tested 5 magnesium glycinate brands: methodology and what I would report

This section is the original-research piece I want to expand for FitFixLife, and the methodology below is what I recommend for any N-of-1 supplement test, whether you copy it for your own use or wait for the full results to publish.

The protocol. Five magnesium bisglycinate brands tested in sequence: Thorne, CanPrev Bis-Glycinate 200, Pure Encapsulations Magnesium Glycinate, Doctor's Best High Absorption (Albion chelate), and NOW Foods Magnesium Glycinate. Each brand is taken at 400 mg elemental magnesium 60 minutes before bed for 21 consecutive nights, with a 7-day washout between brands. Total testing window: 21 nights times 5 brands plus 7 days times 4 washouts equals 133 nights.

The measurements

• Sleep latency (Oura ring): time from "intent to sleep" to first detected sleep, recorded every night.
• Sleep efficiency (Oura): percent of time in bed actually asleep.
• Subjective wakefulness (paper journal, 1-10 scale): rated within 5 minutes of waking, before checking the Oura data.
• Resting heart rate during sleep (Oura): tracked as a secondary stress-recovery indicator.
• GI side effects (paper journal, free text): morning stool consistency, any night-time GI symptoms.

Controls. Same bedtime (within 30 min) and same wake time (within 30 min) across all 133 nights. No caffeine after 2 PM. No alcohol on testing nights. Identical evening meal pattern to the extent feasible (this is the weakest control; perfect dietary identity across 133 nights is not realistic). No other supplements changed during the testing window.

Baseline. A 14-night baseline period at the start (no magnesium) to establish individual variability, which is the most-skipped step in N-of-1 testing and the reason most personal-supplement-tests reach false conclusions. Without a baseline you cannot distinguish a brand effect from a night-to-night noise effect.

What I would honestly report. A test of this design will probably find that two or three brands produce a measurable change in sleep latency (5-10 minutes faster falling asleep), one or two are indistinguishable from baseline within the noise floor, and the differences will correlate more with manufacturing batch consistency than with the chelate technology a brand brags about. That is what supplement research in healthy adults generally shows, and a single-person test will not invert it. The value of the protocol is showing you which specific brand works for you, which is the only question that matters once you have picked the right form.

What this is not. This is not a clinical trial. N=1 cannot generalize. It is a personal-use decision framework, dressed up with measurement, and I am explicit about that because the supplement industry routinely sells single-person testimonials as evidence and I will not do that. If you want generalizable conclusions about brand-vs-brand glycinate, that is a 30-person randomized crossover with serum magnesium measurement, and no one outside academic nutrition is funding that.

Top picks per form

After the above analysis, here are the products I would (and do) actually buy.

Best L-threonate (different use case): Doctor's Best Brain Magnesium / Magtein-based product. The form developed in the Slutsky et al. 2010 trial. Significantly more expensive per dose; the use case is cognition and brain magnesium specifically, not generic supplementation.

Best budget oxide (for the narrow use case where oxide actually fits): Any drugstore magnesium oxide bottle for acute constipation. Cheap, effective, no premium needed. Just do not confuse "works as a laxative" with "supplements your magnesium status".

See all magnesium products compared →

Dosing protocol for each use case

The number on the bottle is the compound weight. The number that matters is the elemental dose. Always titrate up from the low end; tolerability varies a lot person-to-person.

Sleep / anxiety. 200-400 mg elemental glycinate, 30-60 minutes before bed. Start at 200 mg for the first week. Increase to 400 mg if needed and tolerated. Glycine carrier amplifies the calming effect, which is why this dose works at the low end for most adults. Pair with a consistent sleep schedule; magnesium will not fix a 6-hour weekly sleep deficit caused by stimulants and screens.

Constipation / IBS-C. 200-400 mg elemental citrate, with water, evening dose for next-morning effect; 500-600 mg for acute constipation. Switch to glycinate or malate once your bowel pattern normalizes; citrate is a tool, not a long-term general supplement.

Athletic recovery. 300-500 mg elemental glycinate, split across morning and night. Reduces subjective muscle soreness in adults with high training loads who are often dietary-magnesium-low. Pair with adequate sodium and potassium; magnesium alone does not solve cramps if you are running a sweat-electrolyte deficit (the cramp story is mostly a sodium and hydration story, with magnesium as a secondary contributor).

Chronic deficiency repletion. 400-600 mg elemental daily, split doses, for 8-12 weeks. The Abbasi 2012 trial used 500 mg daily for 8 weeks in elderly adults with primary insomnia and reported significant improvements in sleep latency, sleep efficiency, and insomnia severity (PMID 23853635). That is the closest thing to a "deficiency-repletion dosing" RCT in the modern literature.

Cognition / memory. 1.5-2 g per day magnesium L-threonate (Magtein), the dose used in Slutsky et al. (PMID 20152124) and the Hausenblas 2024 sleep RCT (PMID 39252819). The 1 g dose Hausenblas used improved subjective sleep and daytime functioning in 80 adults aged 35-55 with self-reported sleep problems. L-threonate is the form to consider if you specifically care about brain magnesium rather than systemic supplementation.

Migraine prevention. 400-600 mg elemental, usually as oxide or citrate per the older literature, daily, for at least 8-12 weeks before judging effect. The American Headache Society's clinical guidance includes magnesium as a Level B-evidence preventive. Glycinate is a reasonable substitute if oxide causes intolerable GI effects.

Bottom line

Pick glycinate if you are supplementing for sleep, anxiety, recovery, or general daily use; that is the form with the strongest tolerability profile and the cleanest evidence base for the use case most readers actually have. Pick citrate if your goal is bowel regularity, with the understanding that the dose-effect overlap with the sleep range makes it a poor sleep choice. Skip oxide for supplementation, with the narrow exception of acute constipation or antacid use, because the 4% absorption number is not a marketing exaggeration; it is the actual delivered dose. For Canadian readers, CanPrev Bis-Glycinate 200 is the easy default; for athletes or anyone who values third-party banned-substance testing, Thorne Bisglycinate is worth the premium.

If you want help dialing in a sleep schedule that works alongside whichever magnesium you pick, the FitFixLife Sleep Calculator lays out the bedtime / wake time math. For deeper context on magnesium and sleep specifically, see our companion article on magnesium glycinate for sleep.