Where a food or nutritional supplement is used in the treatment of a medical condition it is designated as a food for special medical purposes - otherwise known as a borderline substance. These products, whilst not being medicines, have the properties of a medicinal product and are used to treat disease. The Advisory Committee on Borderline Substances (ACBS) approves a large range of products which are listed in the Drug Tariff in Part XV Borderline Substances (Scotland uses the England and Wales Tariff for borderline substances). These products have been approved for prescribing for the relevant medical condition and the prescription should be endorsed 'ACBS'. A number of specialist formulae are listed in the Drug Tariff for the management of milk protein sensitivity, lactose intolerance and gastro-oesophageal reflux.

It should be noted that even if a product is not specifically named in Part XV it can still be prescribed and the pharmacy will be reimbursed, provided it is not on the blacklist. However, the prescriber may be asked to justify why an approved substance was not prescribed. Clearly, standard formulae not being used to manage a medical condition are not prescribable.