Aside from using someone's else's medications, which others have cautioned about
already, taking medications after their expiration date can cause problems . Some medications can loose their potency, which means that they won't be as strong as they were while still within their life expectancy, but others increase in potency and can also have the additives in them break down or otherwise go bad and can cause an overdose.
It is never a good idea to keep medications past their expiration date. Any one having medications past their expirations, previous prescriptions that they didn't finish, should take them to their pharmacist to dispose of.
Also , anyone who is in pain management needs to keep in mind that taking old prescriptions, even ones previously prescribed to you, can get you into serious trouble with your PM, just as going to another doctor can. Most PM's feel that if you take an old or previous script that they have given you, or another doctor has given you, that you are violating your contract and that can get your dismissed from PM altogther. Be careful guys, I don't want to see anyone get into trouble.
Sandi