Objective The purpose of this study was to evaluate the effects of adding music therapy (MT) to cognitive-behavioral therapy (CBT) on symptoms of smartphone/internet addiction and psychiatric comorbidities. Methods Overall, 155 patients diagnosed with addiction were assigned to either the CBT-MT group or CBT group. Both groups received CBT for 8 weeks, while the CBT-MT group received additional MT. The intervention was completed by 67 and 71 participants in the CBT-MT and CBT groups, respectively. Results The total scores of Young Internet Addiction Scale (YIAT) and Smartphone Addiction Proneness Scale (SAPS) decreased significantly (p<0.001 for both) in both groups, while the total scores of State Anxiety Inventory for Children (SAIC) (p<0.001), Trait Anxiety Inventory for Children (TAIC) (p<0.001), Conners-Wells’ Adolescent Self-Report Scale-Short form (CASS(S)) (p=0.048), and Barratt Impulsiveness Scale-11 (BIS-11) (p<0.001) decreased only in the CBT-MT group. The decrements in YIAT (p=0.025), SAIC (p=0.043), TAIC (p=0.011), and BIS-11 (p=0.012) in the CBT-MT group were significantly greater than those in the CBT group. Conclusion Combined MT and CBT improved the symptoms of smartphone/internet addiction, anxiety, and impulsivity in adolescents. This combination could therefore be an effective treatment of smartphone or internet addiction along with behavioral disorders such as anxiety and impulsivity.Objective The purpose of this study was to evaluate the effects of adding music therapy (MT) to cognitive-behavioral therapy (CBT) on symptoms of smartphone/internet addiction and psychiatric comorbidities. Methods Overall, 155 patients diagnosed with addiction were assigned to either the CBT-MT group or CBT group. Both groups received CBT for 8 weeks, while the CBT-MT group received additional MT. The intervention was completed by 67 and 71 participants in the CBT-MT and CBT groups, respectively. Results The total scores of Young Internet Addiction Scale (YIAT) and Smartphone Addiction Proneness Scale (SAPS) decreased significantly (p<0.001 for both) in both groups, while the total scores of State Anxiety Inventory for Children (SAIC) (p<0.001), Trait Anxiety Inventory for Children (TAIC) (p<0.001), Conners-Wells’ Adolescent Self-Report Scale-Short form (CASS(S)) (p=0.048), and Barratt Impulsiveness Scale-11 (BIS-11) (p<0.001) decreased only in the CBT-MT group. The decrements in YIAT (p=0.025), SAIC (p=0.043), TAIC (p=0.011), and BIS-11 (p=0.012) in the CBT-MT group were significantly greater than those in the CBT group. Conclusion Combined MT and CBT improved the symptoms of smartphone/internet addiction, anxiety, and impulsivity in adolescents. This combination could therefore be an effective treatment of smartphone or internet addiction along with behavioral disorders such as anxiety and impulsivity.