Final answer:
The medical assistant should gather more information about the issue and consult the healthcare provider when a patient reports that a medication is not working.
Step-by-step explanation:
When a patient calls to report that a medication is not working, the medical assistant should respond by gathering more information about the issue and consulting the healthcare provider. Option C is the correct response in this situation. Stopping the medication immediately without consulting a healthcare provider can have adverse effects, and suggesting an over-the-counter alternative without knowledge of the patient's specific condition can be unsafe. Asking the patient to come in for a new prescription may not be necessary if the issue can be resolved by adjusting the current prescription.