If you did alcohol (such a socially accepted norm) then you can do codeine.
I would say for physical Withdrawal, the first 5 -7 days is the worst . After that I found the mental stuff really tough to deal with. I just felt so low. BUT like everything both good and bad, it doesn’t last. Keep your goal firmly in your mind and take one day at a time. If you are an AA person, you will be familiar with ODAAT. Small chunks might be easier than thinking forever.
I too gave up alcohol as I am generally an addictive person and like you, my dad had issues.
So proud of you Dotty! xx