The pharmacist is a character in the Season 3 episode "Through the Looking Glass, Part 2".
She refused twice to fill a prescription for Jack. The first time, she told Jack that he had no further refills remaining. When he presented her with a different prescription, she refused to fill it as well, telling Jack he cannot write a prescription for himself. Jack became frustrated, stating that his father wrote the prescription. However, when she then started to call the number on the prescription to confirm it with his Christian Shephard, Jack stormed off knowing that she could not reach his father.