Is pepper spray effective past the expiration date?

Question

If so, about how long?

Answer 1

An expiration date is legally the last possible date at which 90% of the active ingredient of a product is viable (usable- and not decomposed). Since they don't have to tell you at what rate it decomposes (but I bet the manufacturer could tell you if you call or write), you need to decide: if it was at 90% effective a year ago, would you trust it be effective on the guy trying to mug you a year later? Are you willing to take that risk? Or is is more sensible to buy a new cannister?
I don't think a month or two would matter, but I wouldn't put it off if I lived in a high-crime neighborhood (and I did!).
Now tetracycline is a different story- you DON'T want to use up expired tetracycline...!
Depends on the product, the use, and the critical need for it to work.

Answer 2

should be effective if, you have not test fired the canister

Answer 3

It'll still hurt, so yeah.