Is codeine usable after its expiration date?

[DEViANCE]

Read this from another source, so just a copy and pate of what I found.

Though totally fictitious lets still evaluate it for educations sake

She found some old codeine phosphate that she had being prescribed once for acute back ache.

However the use by date was November last year.
These dates are there for a reason and from research she knows some meds do 'go bad' and have possible toxic effects once the shelf life is overcome.

Anyone have some advice on what the possible adverse effects would be (if any) Codeine after the use by date has expired.

Regards