Obviously, it is not recommended to use insulin after the expiration date. Insulin proteins break down over time and it’s impossible to predict how well expired insulin will work. It won't make you sick, but it will be less effective, and it can be dangerous to use.
There are two different expiration dates that insulin users should be aware of. The unopened expiration date is generally one year after the purchase date and can be found on the box or vial of insulin. Once you open a vial of insulin or pen, another expiration date starts. Generally, insulin expires 28 days after it's opened.
It's important to read all the information on your packaging and speak to your healthcare provider about when your insulin expires after opening it. To help you keep track of the expiration date, it may be helpful to write the date that you opened the insulin on the package or vial.