I took codeine while pregnant, and was told by FIL (GP) to only ever take it for 3 days in a row, and NEVER once labour started, as it can affect the bub.
I had plain prescription codiene (Im allergic to paracetamol) and took it under medical supervision. It was only around 100mg 2-3 times a day, when the pain was too bad.
That small a dose, long term, has impaired my liver and kidney function