The short answer
Check three things: the elemental magnesium per serving (not the compound weight on the front), how many capsules a serving is, and the form. Then compare the cost per 100 mg of magnesium, which our calculator works out. For most people, a plain citrate or glycinate product is good value; expensive blends rarely add anything proven.
On this page
Why is the number on the front misleading?
Because it is often the weight of the whole compound, not the magnesium in it. “Magnesium citrate 1,000 mg” might deliver about 160 mg of magnesium; “magnesium glycinate 500 mg” about 70 mg. The magnesium content is usually in the nutrition table on the back, sometimes with a percentage of the nutrient reference value (NRV). In the EU and UK, the NRV for labelling is 375 mg, so 100% NRV means 375 mg.
What should you check?
- Elemental magnesium per serving. This is the dose. Aim for a product that lets you take 100 to 300 mg a day without exceeding 400 mg.
- Serving size. “Per 4 capsules” is common. Divide to get the amount per capsule.
- The form. Citrate and glycinate are good defaults. Products listing oxide first will hold a lot of magnesium but may loosen stools. “Buffered” glycinate often means part oxide.
- Other ingredients. Blends with zinc, vitamin B6, melatonin (prescription-only in the UK), ashwagandha or herbs change the safety picture and are rarely tested as combinations.
- Claims. UK law allows a few approved health claims for magnesium, such as contributing to normal muscle function or the reduction of tiredness and fatigue. Claims that it cures insomnia, anxiety or migraine are not permitted.
How do you compare prices?
Use the calculator above. It converts any label into the cost per 100 mg of elemental magnesium, so you can compare a tub of capsules with a pouch of powder or a pricey branded form on equal terms.
Which product types are best value?
- Powders of magnesium citrate are usually the cheapest well-absorbed option.
- Capsules and tablets of citrate or glycinate are convenient and widely available.
- Gummies, liquids and sprays cost the most per milligram, and sprays and bath products probably don’t raise magnesium at all.
- Branded forms such as magnesium L-threonate cost many times more per milligram, with little independent evidence. See L-threonate.
Do we recommend brands?
Not yet. We take no money or free products from supplement companies. We plan to publish a UK label audit comparing magnesium products on stated dose, form and cost per 100 mg; until then, the checklist and calculator on this page will get you most of the way.
Common questions
What should I look for on a magnesium label?
The amount of magnesium per serving in the nutrition table, the number of capsules in a serving, the form or forms used, and whether the product contains other active ingredients. Ignore large front-of-pack numbers until you have checked what they refer to.
Are expensive magnesium supplements better?
Not necessarily. Price often reflects branding, trademarked forms or extra ingredients rather than better evidence. Compare products by the cost per 100 mg of elemental magnesium in a form that suits you.
Are magnesium gummies any good?
They can work, but they usually contain little magnesium per gummy, often with added sugar, so you need several a day and they cost more per milligram. Check the label carefully.
Is magnesium from a pharmacy better than from a supermarket?
Not in itself. Food supplements in the UK are regulated as foods wherever they are sold. What matters is the form, the dose and whether the label is clear.
References
First published 4 November 2026. Spotted an error? Tell us and we'll correct it. Read our editorial policy.