Final answer:
The medical assistant should choose option C, inquiring about specific symptoms and reporting to the doctor, as this allows for a professional and responsible approach to the patient's concern about their medication not working.
Step-by-step explanation:
When a patient calls into the office to report that medication is not working, the correct response would be option C: Inquire about specific symptoms and report to the doctor. As a medical assistant, it is important to gather as much information as possible regarding the patient's condition and communicate this effectively to the healthcare provider. Advising the patient to immediately stop taking their medication or disregarding their concerns without a proper assessment could lead to adverse health consequences, and are not advisable actions.