How to read a supplement label, a UK checklist

A vitamin D tub can say "200%" on the back and still give exactly what the NHS advises. That's no misprint. The percentage compares the dose with a labelling reference of 5 µg, while the NHS says adults need 10 µg a day [1][2].

Supplement labels are full of figures like that. This guide reads a label from top to bottom, with a short checklist at each step. It covers the UK rules, %NRV, mineral weights, extract ratios, claims and what "third-party tested" means.

What must a UK supplement label show?

In Great Britain, supplements are regulated as food, not medicines [3]. The rules set out what every label must carry [3][4]. Check for these.

• The name "food supplement". The FSA says it must not be "dietary supplement".
• The type of nutrient or substance the product is built around.
• The daily portion, with a warning not to go over it.
• A statement that supplements shouldn't replace a varied diet.
• A reminder to keep it out of reach of young children.
• The amount of each vitamin, mineral or other active substance per daily portion, in numbers.
• A business name and address.

Those amounts are averages, based on the maker's own analysis of the product [4].

Blends follow the same rule. The law asks for the amount of each substance with a nutritional or physiological effect [4]. So look for a figure beside every active ingredient, not one total for the mix. Our nootropic stacks guide shows how to read a stack's label.

What does %NRV mean?

NRV stands for nutrient reference value. It's a fixed figure set in law for each listed vitamin and mineral, and labels must show each one's amount as a percentage of it [1][4].

Think of it as a yardstick, printed the same on every pack. It isn't a target set for you, and it doesn't always match NHS figures.

So a higher percentage isn't better or worse by itself. For magnesium, the NHS says 400 mg or less a day from supplements is unlikely to cause harm [5].

Plant extracts have no NRV, so there's no percentage beside them [4]. You may see "No NRV" there instead.

Elemental or compound weight?

In a capsule, a mineral comes as a compound, bound to a partner such as glycine or citrate. The compound's weight includes that partner. The elemental weight is the mineral alone, and it's the figure the law asks for, with its %NRV [4].

The gap can be large. Magnesium bisglycinate is about 14% magnesium by weight [6]. So 1,000 mg of the compound gives about 140 mg of magnesium.

Check that the label names the mineral itself, with a %NRV beside it. Our magnesium glycinate guide has a capsule check that does the sum for you.

How do you read an extract ratio?

An extract ratio, such as 10:1, compares the dried plant used with the extract made from it. European medicines regulators call it the drug extract ratio [7]. A 10:1 extract took about 10 kg of plant to make 1 kg of extract.

Some labels multiply the extract weight by the ratio, as in "equivalent to 5,000 mg dried herb". That figure describes the plant that went in, while the capsule holds the extract weight. It's a bit like describing a carton of juice by the oranges squeezed to make it.

A ratio doesn't say which compounds came through. A standardised extract is adjusted to a set content of a named compound [7], and labels give it as a percentage, such as "5% withanolides" or "20% bacosides". Multiply to find the amount. So 500 mg at 20% gives 100 mg of bacosides.

GB food supplement rules don't ask for a ratio or a percentage [4], so not every label has one. For any plant ingredient, check for these.

• The plant's Latin name and the part used, such as root, leaf or fruiting body.
• The extract weight per daily portion.
• A named compound with its percentage, if the extract is standardised.

Our nootropic label calculator turns these figures into amounts for common extracts. The label sections in our ashwagandha and lion's mane guides cover what to look for on each.

What can a supplement label claim?

Claims have their own rules. Three kinds turn up on labels.

• Authorised claims. These use set wording from the GB register, such as "Magnesium contributes to a reduction of tiredness and fatigue". Each comes with conditions of use [8].
• On-hold plant claims. Claims about plants sit on a separate list, still under consideration. The government's spreadsheet holds 2,095 of them and says they may continue to be used in Great Britain, under its guidance [9].
• Disease claims. No food, supplements included, may claim to prevent, treat or cure a disease [10].

One more mark is worth knowing. A pack with a nine-digit number starting "THR" is a registered traditional herbal medicine, not a food supplement [11]. Its uses are based on traditional use rather than evidence that it works [12].

What "third-party tested" means

It means a lab outside the company tested the product. The GB supplement rules and guidance we read don't define the phrase [3][4]. So ask three questions.

• Tested for what? Identity, strength, heavy metals, microbes or substances banned in sport.
• Which batch? The lab report, often called a certificate of analysis, should carry a batch number that matches your pack.
• Against what limit? In GB, food supplements may hold no more than 3.0 mg/kg of lead, 1.0 mg/kg of cadmium and 0.1 mg/kg of mercury [13].

Who tested matters too. UKAS, the UK's accreditation body, assesses food labs against the ISO/IEC 17025 standard, including staff competence and test methods [14].

Testing is there for a reason. Lab studies have found ashwagandha products that didn't match the withanolide level on their labels [15][16], and products sold as rhodiola without its marker compound [17]. Our ashwagandha powder vs capsules guide has the figures.

If you compete in tested sport, look for products checked by a sport testing scheme. A 2026 review of 44 studies found stimulants and steroids that weren't declared on the label in some supplements, most often sport and pre-workout products. It named nootropic products as an emerging category too [18].

Where Nooroots fits

Our labels follow the same layout. Triple Magnesium lists each of its three forms by compound weight, then 301 mg of elemental magnesium per three capsules, 80% of the NRV.

Ashwagandha + Lion's Mane lists 120 mg of KSM-66 ashwagandha root extract at 5% withanolides, which is 6 mg, and 500 mg of lion's mane fruiting body extract at 30% polysaccharides, which is 150 mg. That's per two capsules, with "No NRV" beside both. It's made in the UK by a maker certified to FSSC 22000, a food safety standard, and it has heavy-metal and microbe test certificates.

Frequently asked questions

What is elemental magnesium?

It's the weight of the magnesium itself, not the whole compound it comes in. Magnesium bisglycinate is about 14% magnesium, so 1,000 mg of it gives about 140 mg [6].

How much elemental magnesium do you need a day?

The NHS says adults aged 19 to 64 need 300 mg a day for men and 270 mg for women. It also says 400 mg or less a day from supplements is unlikely to cause harm [5].

What does standardised extract mean?

It's an extract adjusted to a set content of a named compound, shown as a percentage such as "5% withanolides" [7]. The percentage lets you work out how much of that compound each dose gives.

Why do UK labels say "food supplement"?

Because the law requires it. In GB, the product must be sold under the name "food supplement", and the FSA says not "dietary supplement" [3][4].

Are supplements regulated in the UK?

Yes, as food rather than medicines. Businesses must register with their local authority and are responsible for making sure what they sell is safe [3].

Is a higher %NRV better?

Not by itself. The NRV is a reference for labels, not personal advice. The NHS advice of 10 µg of vitamin D a day already shows as 200% NRV [1][2].

References

Every study here is listed so you can read it yourself. This guide is for general information and doesn't replace advice from your GP or pharmacist. We check it again at least every six months.

1. Regulation (EU) No 1169/2011 on the provision of food information to consumers, Annex XIII Part A (nutrient reference values), as it applies in Great Britain. legislation.gov.uk
2. NHS. Vitamins and minerals: vitamin D. Page last reviewed 3 August 2020. Accessed 30 October 2026. nhs.uk
3. Food Standards Agency (2018). Food supplements: guidance for businesses. Published 2 July 2018. Accessed 30 October 2026. gov.uk
4. The Food Supplements (England) Regulations 2003 (SI 2003/1387), regulation 6. Scotland, Wales and Northern Ireland have matching regulations. legislation.gov.uk
5. NHS. Vitamins and minerals: others (magnesium section). Page last reviewed 3 August 2020. Accessed 30 October 2026. nhs.uk
6. National Library of Medicine. PubChem compound summary: magnesium glycinate (CID 84645), molecular weight 172.42 g/mol. Accessed 30 October 2026. pubchem.ncbi.nlm.nih.gov
7. European Medicines Agency, Committee on Herbal Medicinal Products (2010). Guideline on declaration of herbal substances and herbal preparations in herbal medicinal products/traditional herbal medicinal products. EMA/HMPC/CHMP/CVMP/287539/2005 Rev.1. ema.europa.eu
8. Department of Health and Social Care. Great Britain nutrition and health claims (NHC) register, spreadsheet of 19 May 2026. Accessed 30 October 2026. gov.uk
9. Department of Health and Social Care. ‘On hold’ health claims on foods (Article 13(1) spreadsheet). Last updated 12 January 2021. Accessed 30 October 2026. gov.uk
10. Regulation (EU) No 1169/2011 on the provision of food information to consumers, Article 7 (fair information practices), as it applies in Great Britain. legislation.gov.uk
11. Medicines and Healthcare products Regulatory Agency (2009). Introduction of the Traditional Herbal Registration Certification Mark. Drug Safety Update, published on GOV.UK 11 December 2014. gov.uk
12. Medicines and Healthcare products Regulatory Agency (2021). The Traditional Herbal Registration (THR) Certification Mark: guidance for business. assets.publishing.service.gov.uk (PDF)
13. Commission Regulation (EC) No 1881/2006 setting maximum levels for certain contaminants in foodstuffs, Annex, as it applies in Great Britain. legislation.gov.uk
14. United Kingdom Accreditation Service. Laboratory accreditation, food (ISO/IEC 17025). Accessed 30 October 2026. ukas.com
15. Zellner L et al. (2025). Determination of withanolides and withanosides in ashwagandha based products using HPLC-drift-tube-ion-mobility quadrupole time-of-flight mass spectrometry. Electrophoresis 46(5–6): 340–346. PMID 39965076
16. Avula B et al. (2026). A comparison of British and US Pharmacopoeia standards for quality of ashwagandha dietary supplements in commerce. Phytotherapy Research 40(8): 4833–4844. PMID 41386716
17. Booker A et al. (2016). The authenticity and quality of Rhodiola rosea products. Phytomedicine 23(7): 754–762. PMID 26626192
18. Al-Saad N, Aljaal S, Alessa J, Santhosh ME (2026). Systematic review of undeclared prohibited substances and pharmacological adulterants in dietary supplements: prevalence, detection, and risks in sport. Frontiers in Sports and Active Living 8: 1740663. PMID 41908212