What everyone else said Erin. I can think of a number of explanations and none of them is a credit to the doctor:
1)Ass covering for war on (some) drugs
2) I-am-the-doctor-and-what-the-previous-doctor-did-and-the-patient's-lived-experience-are-of-no-account syndrome.
3)Suffering is good for the character.
At any rate this a doctor who will someday kill a patient and then argue that "nobody could have forseen". Ought to have license revoked but won't happen.