If you have migraine and you are not on magnesium, we should talk about why.
Magnesium is one of the most well-studied supplements in headache medicine. It is one of the few supplements that has earned a Level A recommendation from the American Academy of Neurology and the American Headache Society for migraine prevention. That puts it in the same evidence tier as some prescription preventives. And yet, most of my patients have either never been told about it or are taking the wrong form.
Why Magnesium Matters for Migraine
Magnesium plays a critical role in neurotransmitter release, cortical spreading depression (the electrical wave thought to underlie migraine aura), and NMDA receptor function. Multiple studies have demonstrated that people with migraine tend to have lower intracellular magnesium levels compared to controls, even when their serum magnesium appears normal.
The landmark meta-analysis by Chiu et al. (2016), which pooled data from 21 clinical trials, found that oral magnesium supplementation significantly reduced both migraine frequency and intensity. This was not a marginal finding — the effect size was clinically meaningful, with most studies showing a 40–50% reduction in migraine days over a 12-week period.
In my practice, I discuss magnesium with virtually every migraine patient. It has a favorable side-effect profile, it is inexpensive, and it works through mechanisms that are distinct from — and complementary to — most prescription preventives.
The Form Matters: Glycinate vs. Oxide vs. Citrate vs. Threonate
This is where most patients go wrong. They walk into a pharmacy, grab the cheapest bottle of "Magnesium 400mg," and assume they are covered. They are usually taking magnesium oxide. And magnesium oxide is, unfortunately, the worst option for migraine prevention.
Magnesium oxide has a bioavailability of roughly 4%. That means if you take a 400mg tablet of magnesium oxide, your body absorbs approximately 16mg of elemental magnesium. The rest passes through your GI tract and often causes diarrhea — which is why magnesium oxide is also sold as a laxative. Some early migraine trials used oxide because it was what was available, and it did show benefit at high doses, but tolerability is poor.
Magnesium citrate is a step up. Bioavailability is better (around 25–30%), and it is widely available. It still has some GI side effects — loose stools are common, particularly at higher doses. For patients who tolerate it well, citrate is a reasonable option. But it is not my first choice.
Magnesium glycinate (also called magnesium bisglycinate) is what I typically recommend. Bioavailability is excellent — among the highest of oral magnesium forms. Glycine itself has calming neurotransmitter properties, which may offer a secondary benefit for patients with migraine-associated sleep disturbance or anxiety. Most importantly, glycinate is dramatically better tolerated in the GI tract. I can count on one hand the number of patients who have reported significant GI issues with glycinate over the past decade.
Magnesium L-threonate has gained attention for its ability to cross the blood-brain barrier and increase brain magnesium levels. The research here is intriguing but preliminary. Most of the threonate data comes from animal models or small cognitive studies. There are no large migraine-specific trials of threonate. It is also significantly more expensive. I do not routinely recommend it for migraine prevention, though I am watching the literature closely.
My recommendation: magnesium glycinate. It has the best combination of bioavailability, tolerability, and cost.
Dosing: How Much and How to Take It
The AAN and AHS guidelines recommend 400–600mg of elemental magnesium daily for migraine prevention. This is the dose supported by the clinical trials.
A critical distinction: that is 400–600mg of elemental magnesium, not 400–600mg of the total compound. A capsule labeled "Magnesium Glycinate 500mg" may contain only 100mg of elemental magnesium — the rest is the glycine molecule. You need to read the supplement facts label and look for the elemental magnesium content.
I typically start patients at 400mg elemental magnesium daily. If they tolerate it well and their migraine frequency has not adequately responded after 12 weeks, I increase to 600mg. Splitting the dose — 200mg in the morning and 200mg in the evening — can improve absorption and further reduce any mild GI effects.
Take magnesium with food. It improves absorption and reduces the already-low risk of stomach discomfort with glycinate.
How Long Does It Take to Work?
This is where expectations need to be set clearly. Magnesium is a preventive, not an acute treatment. It does not stop a migraine that is already happening.
You need a minimum of 8–12 weeks of daily, consistent supplementation before you can evaluate whether magnesium is working. Some patients notice a gradual reduction in migraine frequency starting around week 4–6, but the full benefit typically takes 3 months to manifest. I tell my patients to commit to 12 weeks before making a judgment.
This is no different from prescription preventives. Topiramate, amitriptyline, and propranolol all require 8–12 weeks for full efficacy assessment. The timeline is a feature of how preventive medicine works, not a limitation specific to magnesium.
Who Should Be Careful
Magnesium is generally very safe, but there are specific populations where physician oversight is essential.
Kidney disease: Magnesium is renally cleared. If you have chronic kidney disease (CKD stage 3 or higher), taking supplemental magnesium without monitoring can lead to hypermagnesemia, which in severe cases causes cardiac arrhythmias. If you have any degree of kidney impairment, do not start magnesium without lab monitoring.
Medication interactions: If you are on a calcium channel blocker (amlodipine, verapamil), discuss magnesium supplementation with your neurologist because of potential additive effects on blood pressure. Similarly, magnesium can interact with certain antibiotics (fluoroquinolones, tetracyclines) by reducing their absorption — separate dosing by at least 2 hours.
Myasthenia gravis: Magnesium can worsen neuromuscular junction transmission. If you have myasthenia gravis, magnesium supplementation should only be considered under close neurological supervision.
How Magnesium Compares to Prescription Preventives
Let me be direct: magnesium is not a replacement for prescription migraine preventives in patients with high-frequency or disabling migraine. If you have 10+ migraine days per month, you likely need a CGRP monoclonal antibody, topiramate, or another first-line preventive.
But magnesium is an excellent complementary therapy. In my practice, most patients on prescription preventives are also on magnesium. The mechanisms of action are different — CGRP antibodies target the calcitonin gene-related peptide pathway, while magnesium works on NMDA receptors and cortical excitability. They are additive, not redundant.
For patients with episodic migraine (fewer than 15 days per month) who prefer to try a supplement before committing to a prescription medication, magnesium is a reasonable first step. I support that approach, provided we set a clear timeline: 12 weeks of consistent dosing, followed by an honest assessment of whether the frequency has meaningfully decreased.
The Bottom Line
Magnesium glycinate at 400–600mg elemental daily is one of the best-supported supplements in headache medicine. It is safe, well-tolerated, inexpensive, and supported by a Level A evidence recommendation. If you have migraine and are not already taking it, bring it up with your neurologist at your next visit.