Worried about expired codeine drops?

I recently took codeine drops for a tickly cough and foolishly ignored the expiration date. The drops had already expired two years ago, and thanks to the internet, I found out that they might have contained potentially carcinogenic substances.

Should I be particularly concerned, and does the risk increase the longer the drops have been expired? Incidentally, this is the first time something like this has happened to me (if that matters).