Health Reference LibraryHow much magnesium should I take, and how much is too much?
This entry is part of the Nutri Tailor Health Reference Library — cited research on supplements, nutrients and adjacent areas of health.
Summary
Most adults do well on 100 to 300 mg of magnesium a day from a supplement, on top of what food supplies, and 400 mg a day is where the NHS draws the line for anything long term. The UK reference intake is 300 mg for men and 270 mg for women from all sources, and most people get about four fifths of that from food, so the supplement is a top up rather than the whole dose. The sleep and stress trials used 250 to 500 mg a day for six to eight weeks. Loose stools are the first sign of too much; real harm is rare unless the kidneys are not clearing it.
Dose calculator: capsules to reach your magnesium target
Enter the daily amount of magnesium you are aiming for and see how many servings of each Nutri Tailor product reach it. Nothing you enter leaves this device. No AI is used.
This tool does arithmetic on the label figures. It is not personal dosing advice and it knows nothing about your history or blood results. The reference intake, the safe upper guide and the trial doses are on this page; talk to your GP or a registered nutritional therapist before changing what you take.
Effective dose
The reference intake is 300 mg a day for men and 270 mg for women aged 19 to 64, from food and supplements together. For most adults, a supplement of 100 to 300 mg a day is enough to close the gap between what food supplies and the reference intake, and 400 mg a day from supplements is the sensible ceiling. The trials for sleep and stress used 250 to 500 mg a day of elemental magnesium for six to eight weeks. Read the elemental figure on the label, not the compound weight, because 1000 mg of magnesium bisglycinate is roughly 140 mg of magnesium.
Safety profile
How much is too much: the NHS says taking 400 mg or less a day from supplements is unlikely to cause harm; more than that can cause diarrhoea in the short term. Loose stools are the first sign, and citrate gets there before bisglycinate. Real toxicity is rare because healthy kidneys clear the excess, but people with reduced kidney function can accumulate magnesium and should not take supplements without their GP. Very high intakes cause nausea, low blood pressure, drowsiness and muscle weakness.
Guideline positions
NHS vitamins and minerals guidance for magnesium. NIH Office of Dietary Supplements fact sheet for magnesium where one exists. The trial doses quoted above are from the sources listed on this page.
Practical framework
Capsules to reach the dose, from the Nutri Tailor range, all made in the UK: [magnesium bisglycinate](/products/magnesium-bisglycinate), 133 mg of magnesium per capsule, so two capsules give 266 mg; [magnesium citrate](/products/magnesium-citrate), 85 mg per capsule, so three capsules give 255 mg; [magnesium malate](/products/magnesium-malate), 63 mg per capsule. To read your own result against the UK ranges, use the free blood test result interpreter. This is a summary of published research, not personal health advice. Talk to your GP or a registered nutritional therapist before changing what you take, especially if you are pregnant, have a diagnosed condition or are under ongoing care.
Common misconceptions
That more magnesium works faster: above the doses the trials used there is no extra effect, only more side effects. That the front of the bottle states the dose: read the per capsule figure and the serving size on the back. That the NHS figure is a toxic threshold: it is the level below which harm is unlikely, which is a different thing.
Sources
- NIH Office of Dietary Supplements. NIH Office of Dietary Supplements — Magnesium Fact Sheet for Health Professionals. NIH Office of Dietary Supplements (US government).
- NHS (UK government) 2025. Vitamins and minerals: others (zinc section). NHS.uk.
- Macian N et al 2022. Short-Term Magnesium Therapy Alleviates Moderate Stress in Patients with Fibromyalgia: A Randomized Double-Blind Clinical Trial. Nutrients. PMID: 35631229 · DOI: 10.3390/nu14102088