I know many fellow allergy families that have an expired epi-pen or two laying around the house. Many of us use it as a training opportunity for caregivers.
I have heard that using an expired epi-pen is ok in an emergency situation, as some medicine is better than none. Only recently did I come across an article that explores this in greater depth. (Thanks to @PremierAllergy on twitter for drawing my attention to it!)
The executive summary: as long as the fluid within is not discolored, an epi-pen retains up to 70% of it's effectiveness even 5-7 years AFTER the expiration date.
My take on this? It's a relief to know that your expired epi-pen could help in an emergency, but don't use that as a reason to carry expired medicine. In an emergency, you want full effectiveness to save your life. You wouldn't chose a doctor that almost has a degree, don't chose a medicine that is almost fully potent.
Please help spread the word. Often we allergy families are better educated about these details than the average EMT or 911 dispatcher because we are immersed in the world of allergy everyday, and thus acquire greater knowledge. Be not only an advocate, but an educated advocate!