A primary care physician is treating a patient who was diagnosed with major depression three months ago. The patient adheres to their prescribed medication but reports that while their mood has slightly improved, they still feel constantly worried, experience frequent muscle tension, and have difficulty concentrating due to persistent, intrusive thoughts. The physician is considering simply increasing the dosage of the current medication. Based on the principles of identifying co-occurring conditions, what is a more effective next step for the physician to consider, and why is this step critical for the patient's long-term outcome?