Magnesium Glycinate vs Citrate vs Oxide vs L-Threonate: Which Form for What

By Dr. Ryan Kneessi, ND, Move Forward Natural Health. Last reviewed October 20, 2026.

“Which magnesium should I buy?” is one of the most common supplement questions. The different forms are magnesium bound to different partner molecules, and that changes how well it is absorbed, how it feels in the gut, and how much magnesium each pill holds. This page compares the four forms people ask about most. It is educational information. For signs that someone may want to look at magnesium in the first place, see Who should consider magnesium.

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The four forms at a glance

Magnesium glycinate (bisglycinate) is magnesium bound to the amino acid glycine. It tends to be gentle on the gut, and people often take it in the evening. Magnesium citrate is magnesium bound to citric acid. It is well absorbed and has a mild laxative effect, which some people want and others do not.

Magnesium oxide provides a lot of elemental magnesium per pill but is absorbed less well, and it has the strongest laxative effect of the four. Magnesium L-threonate is magnesium bound to threonic acid, a form developed for its ability to raise magnesium in the brain in animal research. It provides relatively little elemental magnesium per capsule, so it is usually used alongside other magnesium intake.

What the research shows about absorption

In a randomized, double-blind study of 46 healthy adults taking 300 mg of elemental magnesium a day for 60 days, magnesium citrate and an amino-acid chelate were absorbed better than magnesium oxide, and oxide performed no differently from placebo on the measures used (Walker 2003). In a small crossover study of people with ileal resection, magnesium diglycinate was absorbed better than oxide by the people with the poorest absorption, and it was better tolerated by all of them (Schuette 1994).

Magnesium L-threonate was developed after a study in rats found it raised brain magnesium and improved learning and memory measures (Slutsky 2010). In a placebo-controlled trial of 109 healthy adults, a formula built on magnesium L-threonate with phosphatidylserine and vitamins C and D was associated with better memory test scores after 30 days (Zhang 2022). Because that formula contained several ingredients, it does not show what threonate does on its own.

For sleep, a small randomized trial of older adults with insomnia found that 500 mg of magnesium a day for 8 weeks improved several sleep questionnaire measures compared with placebo (Abbasi 2012). That study did not compare forms.

Label dosing and how much magnesium you are getting

Magnesium labels list both the compound and the elemental magnesium. Elemental magnesium is the number that matters for comparing products and for safety. Many glycinate and citrate products provide about 100 to 200 mg of elemental magnesium per serving, and L-threonate products often provide about 144 mg from a 3-capsule serving, so check the Supplement Facts panel on the product you choose. For example, Pure Encapsulations Magnesium (glycinate) provides 120 mg of elemental magnesium per capsule. Practitioner brands such as Pure Encapsulations, Thorne, Metagenics, Designs for Health, Douglas Laboratories, and Klaire Labs all make magnesium glycinate. According to the NIH Office of Dietary Supplements, the upper limit for magnesium from supplements is 350 mg a day for adults, because higher amounts commonly cause diarrhea and cramping. Clinicians sometimes recommend more for specific reasons, and that should be under their guidance.

A common start-low schedule

Practitioners commonly suggest starting with one serving a day, often in the evening, and increasing over a week or two if your digestion is comfortable. Loose stools are the usual sign that you have reached your limit for that form. This is a general description, so please follow your own clinician’s plan.

Timing and pairing

Glycinate is often taken in the evening, while citrate is often taken at a time when its laxative effect is convenient. Magnesium can be taken with or without food, and taking it with a meal may make it easier on the stomach.

Magnesium can reduce absorption of some antibiotics (tetracyclines and quinolones) and of bisphosphonate bone medications. The NIH suggests taking these antibiotics at least 2 hours before or 4 to 6 hours after a magnesium supplement, and keeping magnesium at least 2 hours apart from bisphosphonates. Some medications, such as certain diuretics and long-term proton pump inhibitors, can change magnesium levels, so ask your prescriber before adjusting magnesium if you take them.

Cautions and who should check with a provider

People with kidney disease should not take magnesium supplements without their doctor’s approval, because the kidneys clear extra magnesium. If you are pregnant or nursing, ask your provider which form and amount is appropriate.

Very large doses of magnesium can cause serious side effects, especially in people with reduced kidney function. Stay within the label and the NIH upper limit unless your clinician advises otherwise.

Pure Encapsulations and Thorne magnesium: label directions

• Pure Encapsulations Magnesium (glycinate): 120 mg of magnesium per capsule. The label on Fullscript says to take 1 to 4 capsules daily with food.
• Thorne Magnesium Bisglycinate powder: 200 mg of magnesium per scoop (3.77 g), lightly sweetened with monk fruit. The label on Fullscript says to mix 1 scoop with at least 8 ounces of water one to two times daily, or as recommended by your health professional. Thorne notes that gas, bloating, or loose stools may occur in some people.

Practitioner-grade options in my Fullscript catalog: if you and your clinician decide a supplement makes sense, my supplement guide by health goal links to the practitioner-grade products I trust.

Frequently asked questions

Related reading

• Who should consider magnesium? Signs, best forms, and safety
• Sleep and Overnight Repair
• Balancing electrolytes on keto
• Brain Health and Cognitive Aging

Sources

1. NIH Office of Dietary Supplements. Magnesium: Fact Sheet for Health Professionals.
2. Walker AF, et al. Mg citrate found more bioavailable than other Mg preparations in a randomised, double-blind study. Magnes Res. 2003;16(3):183-91. PubMed 14596323
3. Schuette SA, Lashner BA, Janghorbani M. Bioavailability of magnesium diglycinate vs magnesium oxide in patients with ileal resection. JPEN J Parenter Enteral Nutr. 1994;18(5):430-5. PubMed 7815675
4. Slutsky I, et al. Enhancement of learning and memory by elevating brain magnesium. Neuron. 2010;65(2):165-77. PubMed 20152124
5. Zhang C, et al. A Magtein, Magnesium L-Threonate, -Based Formula Improves Brain Cognitive Functions in Healthy Chinese Adults. Nutrients. 2022;14(24):5235. PubMed 36558392
6. Abbasi B, et al. The effect of magnesium supplementation on primary insomnia in elderly: A double-blind placebo-controlled clinical trial. J Res Med Sci. 2012;17(12):1161-9. PubMed 23853635

Talk with your own doctor or healthcare provider about the right dose for you before starting any supplement, especially if you’re pregnant, nursing, or take medications.

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This page shares general educational information and is not medical advice. These statements have not been evaluated by the Food and Drug Administration. Talk with your healthcare provider before starting any supplement, especially if you take medications, are pregnant or nursing, or have a health condition. Product labels can change, so always follow the label on the bottle you have.