should we discard medicines whose expiry date is due but has been opened 6 month or a year back

A. Two theories associated with that I would like to tell you that First is specially for kids when we talk about when it is a syrup the power reduces with progressing time but the medicine can be used till its shelf life till the time it is not a powder antibiotic so if you want you can use it but the effect it has reduces a little bit so you can use it and you can discard when it expires