Last updated: September 26, 2026 · Originally published: September 23, 2026 · By Eternal Elixir Editorial
Magnesium L-threonate side effects are uncommon and mild in the published trials. The ones recorded were loose stools, stomach pain and headaches, each affecting a few per cent of people, at rates close to placebo. A standard 2,000mg serve supplies about 144mg of elemental magnesium, well under the 350mg a day that the Australian and New Zealand Nutrient Reference Values set as the upper level for magnesium from supplements.
The people who need care are those with reduced kidney function, anyone already taking another magnesium product, and anyone on certain antibiotics, bone medicines or rosuvastatin, where timing matters. This guide covers each of those with the study behind it, and our magnesium L-threonate guide for Australia covers the wider evidence.
Key takeaways
- In a 6-week Perth trial of 100 adults taking 2,000mg a day, 10% of the magnesium group and 8% of the placebo group had a side effect judged possibly related to the capsules.
- A 2,000mg serve holds about 144mg of elemental magnesium, roughly 41% of the 350mg upper level for supplemental magnesium.
- Diarrhoea is the first sign of too much supplemental magnesium, which is why that upper level exists.
- Space it at least 2 hours from bisphosphonates, and take tetracycline or quinolone antibiotics 2 hours before or 4 to 6 hours after it.
- If your kidney function is reduced, talk to your doctor before taking any magnesium supplement.
Eternal Elixir makes Magnesium L-Threonate 2000mg, and it is our pick for Australians who want this form: the full 2,000mg trial amount in three capsules, with the elemental magnesium printed on the label.
Magnesium L-Threonate Side Effects Recorded in the Clinical Trials
Four randomised, placebo-controlled trials of magnesium L-threonate have published safety data. Here is what each recorded.
| Trial | Who took part | Daily dose | Length | Side effects recorded |
|---|---|---|---|---|
| Lopresti, 2026 (Perth) | 100 adults aged 18 to 45 unhappy with their sleep | 2,000mg | 6 weeks | Possibly related effects in 10% on magnesium and 8% on placebo: loose stools 2 vs 1, stomach pain 2 vs 2, headaches 2 vs 1, skin rash 1 vs 0; no one on magnesium stopped because of a side effect |
| Hausenblas, 2024 | 80 adults aged 35 to 55 with sleep complaints | 1,000mg | 21 days | 4 events on magnesium (leg cramps 2, night waking 1, sunken eyes 1) and 13 on placebo; none rated probable |
| Liu, 2016 | 44 adults aged 50 to 70 with memory complaints | 1,500 to 2,000mg by body weight | 12 weeks | 17 events in 13 of 25 people on magnesium, 30 events in 15 of 26 on placebo; mostly mild, none serious; gut complaints in 5 vs 4 people; blood pressure and heart rate unchanged |
| Zhang, 2022 | 109 healthy adults in China aged 18 to 65 | 2,000mg of a blend with phosphatidylserine and vitamins C and D | 30 days | Reported as well tolerated and safe within the study’s limits |
Read together, the trials show a short safety record with no warning signs. Side effects appeared at similar rates on magnesium and placebo, and they were the kind that come with any capsule: an upset stomach, looser stools or a headache.
The limits are just as clear. The longest trial ran 12 weeks, the largest had 109 people, and three of the four had direct industry links. Threotech funded the Perth trial and supplied the product. Half the authors of the 2024 trial worked for AIDP, a US supplement ingredient company. The 2016 trial was run by Neurocentria, the company that developed the compound, and the 2022 trial tested a branded Magtein blend. None of that makes the results wrong, but it is a reason to want larger independent trials.
If you are still deciding whether the form suits you, our breakdown of magnesium L-threonate benefits sets out what those same trials found on memory and sleep.
Why This Form Causes Few Gut Side Effects
Too much magnesium from supplements shows up first in the gut. The Nutrient Reference Values chose diarrhoea as the deciding endpoint when they set the 350mg upper level, because it is the first sign of excess intake. The lowest intake linked to it was 360mg of magnesium a day from non-food sources.
That makes elemental magnesium the number to watch, not the compound weight on the front of the bottle. Magnesium L-threonate carries relatively little of it. Our label states that 2,000mg of magnesium L-threonate provides about 144mg of elemental magnesium, which is roughly 41% of the upper level.
The forms most often reported to cause diarrhoea, according to the NIH Office of Dietary Supplements, are magnesium carbonate, chloride, gluconate and oxide. The Perth trial authors noted that loose stools, the usual magnesium complaint at higher doses, were not a feature of their trial or of other trials of this ingredient. Our reading is that the small elemental dose per serve explains much of that, although no trial has compared forms head to head for gut effects.
This also explains why a bad experience with one magnesium product does not predict the next. A capsule that supplies several hundred milligrams of elemental magnesium in a form linked to diarrhoea is a different proposition from 144mg of magnesium L-threonate. Our guide to choosing between magnesium supplements in Australia compares the forms.
Who Should Avoid Magnesium L-Threonate
Most healthy adults in the trials took it without trouble. These groups should get medical advice first.
- Reduced kidney function. Healthy kidneys clear surplus magnesium. When kidney function is impaired, the body’s ability to remove excess magnesium drops, and the risk of magnesium toxicity rises. If you have reduced kidney function or are on dialysis, do not take a magnesium supplement unless your doctor says so.
- People already taking another magnesium product. The 350mg upper level covers all supplemental magnesium together. Add up the elemental magnesium across every product you take, including multivitamins and some antacids and laxatives.
- Pregnancy and breastfeeding. The upper level of 350mg applies in pregnancy and breastfeeding too, but we found no magnesium L-threonate trial in pregnant or breastfeeding women. Talk to your doctor or midwife first.
- Inflammatory bowel conditions. Because diarrhoea is the first sign of excess magnesium, talk to your gastroenterologist before adding a magnesium supplement if you have an inflammatory bowel condition.
- Anyone on regular prescription medicines. See the timing table below, and ask your pharmacist.
Very large doses of magnesium are where real toxicity lives. The NIH Office of Dietary Supplements notes that magnesium toxicity has been linked to very large doses of magnesium-containing laxatives and antacids, typically more than 5,000mg a day. A standard magnesium L-threonate serve is a small fraction of that.
If magnesium does not agree with you and calm evenings are your goal, our saffron extract capsules are a different ingredient to read about, and our guide to magnesium L-threonate for sleep covers timing.
Medication Timing: What Not to Take Magnesium L-Threonate With
Most magnesium interactions are about absorption, and spacing the doses usually solves them. The timings below come from the NIH Office of Dietary Supplements magnesium fact sheet, except rosuvastatin, which comes from a separate study.
| Medicine | What happens | What to do |
|---|---|---|
| Oral bisphosphonates, such as alendronate | Magnesium can reduce how much of the medicine you absorb | Take magnesium at least 2 hours before or after |
| Tetracycline antibiotics, such as doxycycline | Magnesium binds the antibiotic in the gut | Take the antibiotic at least 2 hours before, or 4 to 6 hours after, the magnesium |
| Quinolone antibiotics, such as ciprofloxacin | The same binding problem | Same spacing as tetracyclines |
| Loop and thiazide diuretics | Long-term use increases magnesium loss in urine | Ask your doctor about your magnesium status |
| Potassium-sparing diuretics, such as spironolactone | Reduce magnesium loss, so magnesium can build up | Ask your doctor before adding magnesium |
| Proton pump inhibitors, taken for more than a year | Can lower blood magnesium | Ask your doctor about checking your levels |
| Rosuvastatin | A magnesium and aluminium antacid taken at the same time cut rosuvastatin levels by 54% | Ask your pharmacist; taking the antacid 2 hours later reduced the effect |
The rosuvastatin row answers a common question. In a study of 14 healthy men, an antacid containing aluminium hydroxide and magnesium hydroxide, taken at the same time as rosuvastatin, reduced the amount of rosuvastatin in the blood by 54%. Taken 2 hours after rosuvastatin, it reduced it by 22%. No study has tested magnesium L-threonate with rosuvastatin, so we cannot say whether it behaves the same way. The cautious approach is to ask your pharmacist and keep the two apart.
The antibiotic spacing protects the antibiotic, which matters more than protecting the supplement. The same logic runs through many supplement interactions, as our guide to berberine drug interactions shows.
How to Reduce Magnesium L-Threonate Side Effects
- Take it with a meal. Our label directs three capsules daily with a meal.
- Split the serve if your stomach objects. The label gives two options: all three capsules in the evening for sleep, or two in the morning and one in the evening for focus. Splitting spreads the magnesium across the day.
- Count your total magnesium. Keep supplemental magnesium from all products under 350mg a day unless your doctor advises otherwise.
- Space it from medicines. Use the table above, and ask your pharmacist if a medicine is not listed.
- Stop and check if symptoms persist. Diarrhoea that does not settle is the classic sign of too much magnesium. If you notice muscle weakness, unusual tiredness or an irregular heartbeat, stop and see a doctor, especially if your kidney function is reduced.
Where you buy matters less than what the label says. Our guide to magnesium L-threonate at Chemist Warehouse covers what the pharmacy chains stock, and our magnesium L-threonate comparison sets the Australian options side by side.
Magnesium L-Threonate vs Other Magnesium Forms
Magnesium L-threonate is magnesium bound to L-threonic acid. It was developed to raise magnesium inside the brain, and the evidence that it does so comes from rat studies, including the 2010 Neuron paper that introduced it. The human trials above measured memory and sleep outcomes rather than brain magnesium.
What the human trials found, in brief: in the Perth trial, the magnesium group improved more than placebo on an overall cognition score and reaction time, and on one self-rated sleep measure, though not on sleep measured by a wearable ring. In the 2024 trial, deep and REM sleep scores from a wearable ring were better on magnesium than placebo over 21 days. These results suggest magnesium L-threonate may support memory and sleep quality in adults, from small, industry-linked trials.
Compared with glycinate or citrate, the main practical difference is how much elemental magnesium you get. No trial has compared magnesium L-threonate with glycinate directly. If your goal is simply topping up magnesium, a form that supplies more elemental magnesium per capsule may suit you better. If your goal is the memory and sleep outcomes tested in these trials, magnesium L-threonate is the form they used.
Eternal Elixir Magnesium L-Threonate: Who It Suits and Who It Doesn’t
Eternal Elixir makes Magnesium L-Threonate 2000mg, so read this as our pick with the working shown. Prices are as of Sep 2026.
- What is in it: 2,000mg of magnesium L-threonate per three-capsule serve (about 144mg elemental magnesium), with rice flour in a vegetable capsule.
- Bottle and cost: 90 capsules, 30 serves, $59.99, which is $2.00 a day. Three bottles at 15% off cost $152.97, or $1.70 a day, and ship free because the order is over $100.
- Testing: our product page states that each batch is tested by a third-party laboratory for identity, potency and purity, including heavy metals and microbes, with the batch certificate available on request.
Who it suits: adults with healthy kidney function who want the dose used in the Perth trial and a label that states the elemental magnesium.
Who it doesn’t suit: anyone with reduced kidney function unless their doctor agrees, people who already take enough supplemental magnesium to approach 350mg a day, and people who simply want the most elemental magnesium per dollar, for whom another form may be better value.
Frequently Asked Questions
Is taking magnesium L-threonate safe?
For healthy adults with normal kidney function, the trials suggest it is well tolerated. Across four placebo-controlled trials of 21 days to 12 weeks, side effects were mild and occurred at rates close to placebo. A standard serve supplies about 144mg of elemental magnesium, under the 350mg upper level for supplemental magnesium. If your kidney function is reduced, do not take it without medical advice.
What not to take magnesium threonate with?
Take it at least 2 hours apart from oral bisphosphonates. Take tetracycline or quinolone antibiotics at least 2 hours before, or 4 to 6 hours after, your magnesium. Avoid stacking it with another magnesium supplement without counting the elemental total. If you take diuretics, proton pump inhibitors or rosuvastatin, ask your doctor or pharmacist.
Add Magnesium L-Threonate to cart · $59.99
Can I take magnesium supplements with rosuvastatin?
Ask your pharmacist first. In a study of 14 healthy men, a magnesium and aluminium antacid taken with rosuvastatin cut rosuvastatin levels in the blood by 54%, and taking the antacid 2 hours later reduced that to 22%. Magnesium L-threonate has not been tested with rosuvastatin, so keeping the two apart is the cautious choice.
Which is better, magnesium glycinate or magnesium L-threonate?
It depends on your goal, and no trial has compared them directly. Magnesium L-threonate is the form used in the memory and sleep trials described above, and it supplies about 144mg of elemental magnesium per 2,000mg serve. If you only want to raise your magnesium intake, a form that supplies more elemental magnesium per capsule may be better value.
Can I take magnesium if I have colitis?
Talk to your gastroenterologist first. Diarrhoea is the first sign of too much supplemental magnesium, and we found no magnesium L-threonate trial in people with inflammatory bowel conditions. If your specialist agrees, starting with one capsule with food lets you judge how your gut responds.
Is there such a thing as magnesium L-threonate withdrawal?
We found no published report of a withdrawal effect. Magnesium is a dietary mineral that you also get from food. If sleep or focus drifts back to where it was after you stop, that is the supplement’s effect wearing off, not withdrawal.
Does magnesium L-threonate cause hair loss?
None of the four trials reported hair loss, and we found no study linking magnesium L-threonate to it. Hair shedding has many possible causes, so if you notice it, see your GP rather than assume the supplement is responsible.
What is the difference between magnesium and magnesium L-threonate?
Magnesium is the mineral; magnesium L-threonate is one compound that delivers it, bound to L-threonic acid. It carries less elemental magnesium per gram than many forms, about 144mg per 2,000mg serve. It was developed to raise brain magnesium, an effect shown in rats, and human trials have tested it for memory and sleep.
The Bottom Line
Magnesium L-threonate has a short, clean safety record: a few mild gut effects and headaches in small trials, at rates close to placebo. The elemental dose is modest, about 144mg per serve, so the upper level is hard to exceed unless you stack products. The real precautions are kidney function and medicine timing.
More safety guides from our range: tongkat ali side effects, berberine side effects, glutathione side effects and TUDCA side effects. Or browse the full range.
Sources
- Lopresti AL, Smith SJ. The effects of magnesium L-threonate (Magtein) on cognitive performance and sleep quality in adults: a randomised, double-blind, placebo-controlled trial. Front Nutr. 2026;12:1729164. PubMed 41601871
- Hausenblas HA, Lynch T, Hooper S, et al. Magnesium-L-threonate improves sleep quality and daytime functioning in adults with self-reported sleep problems: a randomized controlled trial. Sleep Med X. 2024;8:100121. PubMed 39252819
- Liu G, Weinger JG, Lu ZL, Xue F, Sadeghpour S. Efficacy and safety of MMFS-01, a synapse density enhancer, for treating cognitive impairment in older adults: a randomized, double-blind, placebo-controlled trial. J Alzheimers Dis. 2016;49(4):971-90. PubMed 26519439
- Zhang C, Hu Q, Li S, et al. A Magtein, magnesium L-threonate, -based formula improves brain cognitive functions in healthy Chinese adults. Nutrients. 2022;14(24):5235. PubMed 36558392
- Slutsky I, Abumaria N, Wu LJ, et al. Enhancement of learning and memory by elevating brain magnesium. Neuron. 2010;65(2):165-77. PubMed 20152124
- Martin PD, Schneck DW, Dane AL, Warwick MJ. The effect of a combination antacid preparation containing aluminium hydroxide and magnesium hydroxide on rosuvastatin pharmacokinetics. Curr Med Res Opin. 2008;24(4):1231-5. PubMed 18355422
- Nutrient Reference Values for Australia and New Zealand: Magnesium. Eat For Health
- NIH Office of Dietary Supplements. Magnesium: Fact Sheet for Health Professionals. ods.od.nih.gov
- Eternal Elixir, Magnesium L-Threonate 2000mg product page (label, directions, elemental magnesium, testing statement), read September 2026.
