Batches of Novo Nordisk's diabetes treatments NovoMix 30 FlexPen and Penfill are being recalled, the European Medicines Agency said on Friday.
"In the affected cartridges the level of insulin may vary between 50 percent and 150 percent of the labelled insulin units, which could lead to hypoglycaemia or hyperglycaemia," the agency said in a statement.
Only a small percentage of cartridges, 0.14 percent, contain the wrong amount, the Danish company said.
Patients whose products were labelled with numbers from the affected batches should "make an appointment with their doctor or nurse for switching treatment as soon as it is feasible," the EU regulator said.
A spokesperson for the company was not immediately available on Friday afternoon.
Novo Nordisk has almost half the global insulin market, which has grown rapidly in recent years following a rise in the number of people suffering from diabetes, estimated by the World Health Organisation to stand at around 347 million.