The UK left the European Union's single market on 1 January 2021. A Withdrawal Agreement made special provision for Northern Ireland. However, 'grace periods' concerning supply of goods were agreed, delaying full application of the new rules. The Northern Ireland NHS is heavily reliant on supplies from Great Britain. If these supplies are disrupted, the quality of care offered to patients will diminish. This article shows the legal details of applicable law once the 'grace periods', which are currently securing supply, cease to apply. It reveals significant costs and uncertainties associated with supply of products to the NHS in Northern Ireland. The direction of travel, unless something changes, is that new products will reach patients later than in Great Britain, and there is a real possibility that some products become difficult or impossible for the NHS in Northern Ireland to source. The result will be reduced quality of patient care.