The aim of the present study was to investigate the effect of teriparatide on device-related vertebral osteopenia after single lumbar spinal interbody fusion and compare osteopenia in fused and nonfused spinal segments using Hounsfield unit (HU) values. The present study was a retrospective cohort study. We reviewed 68 consecutive patients (28 men and 40 women) who underwent single-segment (L4-5) transforaminal lumbar interbody fusion with cage and pedicle screw fixation. The patients were divided into 2 groups according to whether they were treated with teriparatide (teriparatide and nonmedication groups). The primary outcome measure was HU values measured on computed tomography images from each L1 to S1 vertebral body12-month postoperatively. Secondary outcome measures were femoral neck bone mineral density (BMD), T-score, osseous union, and clinical outcomes using the Japanese Orthopedic Association scoring system 12-month postoperatively. There were significant decreases in HU values of lumbar vertebral bodies at all levels and BMD and T-score values obtained using dual-energy X-ray absorptiometry of the femur between preoperative and postoperative 12-month computed tomography in the nonmedication group (P < .05). On the other hand, there were no significant differences between properative and postoperative 12-month HU values of each lumbar vertebral body and BMD values of the femur in the teriparatide group. Osseous fusion scores in the teriparatide group were significantly better than those in the nonmedication group. There were no significant differences in postoperative Japanese Orthopedic Association scores between the 2 groups. Administration of teriparatide during the perioperative period may prevent bone loss associated with spinal fusion surgery.