Final answer:
The medical assistant should instruct the patient to continue taking the medication and schedule a follow-up appointment.
Step-by-step explanation:
The medical assistant should respond by instructing the patient to continue taking the medication and scheduling a follow-up appointment. This allows the healthcare provider to assess the patient's response to the medication and make any necessary adjustments. Discontinuing the medication immediately or doubling the dose without medical guidance can be potentially harmful. Ignoring the patient's concerns is not appropriate, as their reported lack of effectiveness should be addressed.