It can be overwhelming walking into the pharmacy and looking down the vitamin aisle – especially when you finally find a specific supplement, only to discover there are numerous forms lining the shelves. This gets even more challenging when you don’t know which salt form will be the most beneficial for your specific needs. We wanted to put together this comparison of magnesium supplements to help you better understand what to look for.
Before diving into the various magnesium salt forms, it’s important to understand magnesium’s role in the body. Normal serum magnesium levels range from 1.8 to 2.2 mg/dL. Magnesium plays many roles in the body, which include supporting muscle and nerve function, maintaining healthy bones, and promoting cardiovascular health. Low magnesium levels are anything <1.8 mg/dL and people may present with muscle spasms, eyelid twitching, and fatigue. Numerous medications can cause low magnesium and I provided a case example in the past on this topic. Magnesium is available in organic (citrate, bisglycinate, L-threonate) and inorganic (oxide and chloride) salt forms, with organic salt forms having better bioavailability. Below is a comparison of magnesium supplements and their common salt forms.
Magnesium Oxide
This is likely the most common form of magnesium due to its easy access and affordability. Magnesium oxide is a less soluble form of magnesium, with decreased rates of absorption and bioavailability. Due to its reduced absorption and potential to cause diarrhea, this oral form may not be ideal for treating magnesium deficiency. It is more often used as an antacid to help treat heartburn and indigestion. It also has an osmotic laxative effect, making it a good choice for managing constipation. However, its use is limited due to its side effect profile including diarrhea, nausea, and abdominal cramping.
Magnesium Citrate
This is one of the most bioavailable forms of magnesium and is readily absorbed in the gut, making it a popular choice amongst consumers. This form is often used to help replace low magnesium levels. Magnesium citrate also has a laxative effect as it increases fluid in the bowels, making it an ideal option for bowel preparation prior to a colonoscopy at high doses. Due to this laxative effect, it’s important that this form of magnesium be avoided in patients with preexisting diarrhea or sensitive stomachs. On average, it is typically more expensive than the oxide formulation.
Magnesium Bisglycinate
Magnesium bisglycinate is a chelated form of magnesium composed of two glycine molecules, similar to the glycinate salt form which is composed of only one glycine molecule. This chelation helps improve bioavailability and reduce the GI side effects common with other salt forms, making it a more appealing option to consumers. This makes it a preferred option for those who need supplementation but cannot tolerate alternative forms. The potential downside is that this formulation tends to be more expensive compared to magnesium oxide.
Magnesium Chloride
Magnesium chloride is available in multiple dosage forms including an oral tablet, oil, lotion, and cream. The tablet formulation has fair absorption in the gut but is prone to causing digestive issues such as an upset stomach, nausea, and diarrhea. This formulation is most commonly used to help with depression, blood sugar levels, and quality of sleep but can also be used to treat magnesium deficiency. Magnesium oil has been used to help with pain related to fibromyalgia, neuropathy, and wound healing. There is even some evidence that the body can absorb small amounts of magnesium transdermally, leading to systemic effects.
Magnesium L-threonate
Magnesium L-threonate is a relatively newer magnesium supplement on the market and has high bioavailability. This salt form is unique compared to the others as it is purported to be able to cross the blood-brain barrier. There was a small study done with this formulation on sleep and daytime function. Unfortunately, it only included 80 participants and was compared against placebo, not other cheaper forms of magnesium. Magnesium L-threonate is on the expensive side for magnesium supplementation and may not be ideal for patients simply wanting to increase systemic levels.
While this is not an exhaustive list of magnesium salt forms, these are likely the most common ones you will see sitting on the shelf at your local pharmacy or vitamin shop. Many clinicians will typically start with the cheapest and most readily available option and monitor magnesium levels in those who are deficient. If the patient is not responding or has adverse effects, alternative salt forms may be considered.
We hope you can benefit from this comparison of magnesium supplements. What magnesium supplement do you see used most often?
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Kelly Chies, PharmD Candidate, wrote this article in collaboration with Eric Christianson, PharmD, BCPS, BCGP
References:
- Allen MJ, Sharma S. Magnesium. [Updated 2023 Feb 20]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2025 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK519036/
- Rude RK. Magnesium. In: Coates PM, Betz JM, Blackman MR, Cragg GM, Levine M, Moss J, White JD, eds. Encyclopedia of Dietary Supplements. 2nd ed. New York, NY: Informa Healthcare; 2010:527-37.
- Schuchardt, J. P., & Hahn, A. (2017). Intestinal Absorption and Factors Influencing Bioavailability of Magnesium-An Update. Current nutrition and food science, 13(4), 260–278.
- Guerrera, M. P., Volpe, S. L., & Mao, J. J. (2009). Therapeutic uses of magnesium. American family physician, 80(2), 157–162.
- Hausenblas, H. A., Lynch, T., Hooper, S., Shrestha, A., Rosendale, D., & Gu, J. (2024). Magnesium-L-threonate improves sleep quality and daytime functioning in adults with self-reported sleep problems: A randomized controlled trial. Sleep medicine: X, 8, 100121.
- Rawji, Alexander et al. “Examining the Effects of Supplemental Magnesium on Self-Reported Anxiety and Sleep Quality: A Systematic Review.” Cureus vol. 16,4 e59317. 29 Apr. 2024.
This was concise and helpful. Thanks for making it easy to understand and share.