Reduces codeinone to codeine in the penultimate step in morphine biosynthesis. Can use morphinone, hydrocodone and hydromorphone as substrate during reductive reaction with NADPH as cofactor, and morphine and dihydrocodeine as substrate during oxidative reaction with NADP as cofactor. codeine + NADP(+) = codeinone + H(+) + NADPH Optimum pH is 6.8 for reduction (forward reaction) and 9.0 for oxidation (reverse reaction). Optimum temperature is 28 degrees Celsius for reduction (forward reaction) and 30 degrees Celsius for reduction (reverse reaction). Alkaloid biosynthesis; morphine biosynthesis. Present in the cytosolic part of laticifer cells that secrete latex. Latex secreting cells (laticifer cells). Expressed constitutively in all organs. Useful marker for the forensic DNA analysis of opium poppy. Belongs to the aldo/keto reductase family.