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Magnesium supplements UK: forms, labels and serving costs
Compare magnesium supplements using the elemental magnesium per serving, the number of capsules in that serving and the complete ingredient list. The weight of a magnesium compound on the front of a bottle is not the amount of elemental magnesium it supplies.
Elemental magnesium versus compound weight
Magnesium is supplied in compounds or mineral mixtures. A label may give the weight of the whole compound and then state how much magnesium it provides. For a nutrient comparison, use the provided magnesium figure. Do not compare a compound’s 1500mg headline with another product’s 198mg elemental amount as if they measure the same thing.
Also check the serving basis. A value for two capsules needs two capsules to supply that stated amount. Dividing by two can help compare labels per capsule, but it does not tell you what dose to take.
Forms and blends: read the ingredient list
Glycinate or bisglycinate, citrate and oxide describe different compounds. “Buffered” can indicate a blend that includes another form. “Marine” describes a source or mixture; it is not a synonym for glycinate. Product names alone may not reveal all the forms in a capsule.
Claims that one product is universally best absorbed, gentlest or best for sleep require evidence relevant to that finished product and use. We have not established those claims for the examples here. A retailer testimonial is not a controlled comparison.
| Label check | Together Health marine magnesium | Simply magnesium bisglycinate |
|---|---|---|
| Elemental amount shown | 198mg per capsule | 300mg per two capsules |
| Form detail | Marine mineral blend | Buffered bisglycinate includes oxide |
| Pack / comparison serving | 30 capsules / one capsule | 120 capsules / two capsules |
| One-off item price | £7.49 | £12.99 |
| Servings / calculated cost | 30 / 25.0p | 60 / 21.7p |
Sources: Together’s label and Simply’s label, checked 3 October 2026. These are purchase examples, not equal-dose alternatives or a ranking of effectiveness.
How to calculate cost per serving
- Divide the capsule count by the capsules in the comparison serving.
- Divide the pack price by that number of servings.
- Add delivery when comparing the total basket.
- Record whether the price needs a subscription or multiple packs.
For example, 120 capsules divided by two gives 60 servings. £12.99 divided by 60 is £0.2165, rounded to 21.7p. Calling this a 120-day supply while using the two-capsule nutrient figure would mix two different assumptions.
Cost per 100mg can be a mathematical comparison, but it encourages a false sense of equivalence across forms and doses. We prioritise the labelled serving and explain its limitations.
Do you need a supplement?
The NHS guidance on magnesium and other nutrients says most people should get the magnesium they need from a varied, balanced diet. It also notes that high supplemental amounts can cause diarrhoea. More magnesium is not automatically better.
Ask a pharmacist or clinician before choosing a supplement if you take medicines or have a condition affecting safe use, especially kidney problems. Persistent symptoms deserve appropriate assessment rather than being treated as proof of a deficiency. Check overlapping supplements so you do not overlook a second source of magnesium.
A practical shortlist
Keep products whose elemental amount, capsule count and complete ingredients are clear. Remove products that do not fit your dietary requirements. Then compare the delivered price and pack size. If you need a particular form, verify that the blend actually meets that requirement before considering the discount.