Supplements are food in law, not medicine
The starting point, which surprises most people, is that a vitamin capsule and a loaf of bread sit under the same broad body of law. Food supplements are regulated as food in Great Britain, with policy and standards work led by the food regulator and enforcement carried out at local authority level, principally by trading standards.
What that framework requires is that the product is safe, that it contains what the label says, that permitted vitamin and mineral forms are used, that labelling and warnings are correct, and that the claims made comply with the rules on nutrition and health claims.
What it does not require, at any point, is evidence that the product produces a benefit. There is no efficacy assessment before sale, no equivalent of a clinical trial programme, and no regulator who reads the science and forms a view about whether the thing works. A product being on sale legally means it complied with food law.
The line between a supplement and a medicine
A product becomes a medicine, in regulatory terms, if it is presented as treating or preventing disease, or if it works by pharmacological, immunological or metabolic means to restore or modify physiological function. Either limb can be sufficient.
Crossing that line moves the product to the Medicines and Healthcare products Regulatory Agency, which requires a licence supported by evidence of quality, safety and efficacy. Products near the boundary are assessed case by case, and the assessment considers presentation as well as composition, which is why marketing language can itself convert a food into an unlicensed medicine.
This explains a great deal about how supplements are written about. Vague mechanistic phrasing, supports, promotes, contributes to, helps maintain, is not evasiveness for its own sake. It is the language that stays on the food side of the line. A product that said it treats a disease would be an unlicensed medicine, which is an offence to sell.
There is a separate route for traditional herbal medicines, which can be registered on the basis of long-standing traditional use and appropriate quality and safety, without evidence of efficacy in the modern sense. A registration under that scheme certifies quality and traditional use. It does not certify that the product works.
How health claims are policed
Nutrition and health claims are the tightly controlled part of the system. Only claims that appear on the authorised register may be made, they must be made in the permitted wording or something with the same meaning, and they may only be attached to a product supplying the substance in the required amount.
Most authorised claims concern established vitamin and mineral functions, which is why the same phrases recur across very different products. Claims about reducing disease risk face a higher bar, and claims relating to children's development are handled separately.
Advertising is policed alongside this by the advertising regulator, which adjudicates complaints and can require that a claim be withdrawn. Enforcement is largely complaint driven and acts after the fact rather than before publication, which means that a claim being visible is not evidence it has been assessed and passed.
The practical consequence for a reader: a phrase on a label that sounds like a health claim has either been authorised, in which case it will be one of a limited set of tightly worded statements about a nutrient, or it is marketing that sits outside the claims rules. Learning to tell the two apart takes about ten minutes and is durable knowledge.
What the rules require, who enforces them and what to do, as at 20 October 2026
The four parts of the system are easy to confuse, so they are set out separately here. Each is checked against the responsible body's own current guidance.
What the law requires before sale
A food supplement must be safe, must contain the permitted forms of the vitamins and minerals it declares, and must carry a defined set of information: the words food supplement rather than dietary supplement, the business name and address, the ingredients with allergens emphasised, the conditions of use including the recommended daily dose and a warning not to exceed it, storage instructions including keeping the product away from young children, a use by or best before date, the amount of each vitamin, mineral or other active substance, and a statement that a supplement should not replace a varied diet. Responsibility for safety sits with the business selling the product. None of that is an assessment of whether the product does anything, and the Food Standards Agency is explicit that a supplement is not a medicinal product and may not be presented as acting pharmacologically, immunologically or metabolically.
Who enforces it
Policy is held nation by nation: the Department of Health and Social Care in England, the Welsh Government in Wales, Food Standards Scotland in Scotland and the Food Standards Agency in Northern Ireland. A business selling supplements registers with its local authority, and the enforcement authorities can require its records, so day to day enforcement is local rather than national. Two other bodies take over at the edges. A product presented as treating or preventing disease, or acting by a medicinal mechanism, becomes a matter for the Medicines and Healthcare products Regulatory Agency and needs a licence. Advertising that makes a claim the rules do not allow is a matter for the Advertising Standards Authority, which acts on complaints after publication rather than approving anything in advance.
Which health claims are allowed
Only the claims entered on the Great Britain nutrition and health claims register may be made, in the authorised wording or in wording with the same meaning for the reader, and only on a product supplying the substance in the amount the entry requires. The register is published and searchable, which makes it the quickest way to settle an argument about a label: if the phrase is not in it, in substance, it is marketing rather than an authorised claim. Claims about reducing disease risk and claims about children's development are handled under stricter conditions, which is why they are rare on a shelf.
What a reader can do with this
Read compliance as compliance and nothing more: a lawful label tells you the product is permitted to be sold and says nothing about effect. For whether a supplement is worth taking at all, the NHS pages on vitamins and minerals set out who may need one and the amounts that are safe over time, and the NHS advises a daily vitamin D supplement through the autumn and winter, when sunlight in the UK is too weak to supply it. If a product seems unsafe or mislabelled, the route is the local authority that registered the business, through trading standards or environmental health. If a suspected reaction involves a licensed medicine or a registered traditional herbal medicine rather than a food supplement, it goes to the Medicines and Healthcare products Regulatory Agency through the Yellow Card scheme.
Novel ingredients, quality and what to do about harm
Ingredients without a significant history of consumption in Great Britain before the novel food cut-off require pre-market authorisation, assessed for safety before they may be sold. Several compounds popular in longevity marketing sit in or near this category, and their status differs between jurisdictions and can change. The regulator's own register is the authoritative source, and the position in one country tells you nothing reliable about the position here.
On quality, the legal requirement is that the product contains what the label states. Verification is not routine before sale, and independent testing programmes have repeatedly found products where content did not match the label. Third party certification schemes exist and are worth more than a manufacturer's own assurance, particularly for anyone subject to drug testing in sport.
Interactions are the most underestimated risk. Supplements can interact with prescribed medicines, and because they are not prescribed they are frequently omitted from the list a patient gives their doctor. Anyone taking anticoagulants, immunosuppressants, epilepsy medicines or hormonal treatments should tell their prescriber what else they are taking.
Suspected side effects from a medicine, including herbal and unlicensed products, can be reported through the regulator's Yellow Card scheme, and reporting matters because the system depends on it for signals. For general guidance on vitamins and minerals, the NHS is the appropriate starting point. For how the underlying evidence should be judged, see our grading methodology and our review of senolytics, where laboratory findings are used to market products with no trial support for the claim.