Can you become less responsive to codeine? i know some can't metabolise it at all, can this occur later in life or only from birth?

Codeine metabolism: The hepatic CYP2D6 enzyme metabolizes codeine into it's metabolite- morphine. 5 to 10% of people have 2 inactive copies of CYP2D6 so they can't metabolize or poorly metabolize codeine. This means that they get poor pain control because of low morphine levels. This is a genetic issue. I assume, but don't know for a fact that this would be present at birth. You can develop a tolerance to opioids.