EpiPens and other adrenaline auto-injectors may still be potent enough to work many months past their labelled expiration date, according to a US study.

Four out of five auto-injectors tested still had 90% or more adrenaline two years beyond their use-by date, indicating they were still effective under the US labelling laws, the researchers note. 

The US Food and Drug Administration (FDA) requires auto-injector expiration dates to ensure that the devices never contain less than 90% of the original dose of adrenaline, the authors say.

For their study, published in the Journal of Allergy and Clinical Immunology: In Practice, researchers tested the contents of 46 different auto-injectors to see how much adrenaline remained after the expiration dates on the labels.