Fig. 1. A flow chart. All 80 participants, who were to receive percutaneous endoscopic lumbar discectomy (PELD) at L4-L5, had already completed basic laboratory examination, including a complete blood count, liver and renal function tests, and electrolyte level tests before hospitalization. They randomly received a mixture of 15 mg of morphine and 270 mg of ketorolac with or without 180 mg of nefopam (NFP) (the NFP group or NS group) using a postoperative intravenous patient-controlled analgesia (PCA) device. The PCA use began with an infusion just before the operation, without a loading dose. The PCA was programmed for a total volume of 100 ml with a basal infusion rate of 1 ml/h, a bolus infusion volume of 1 ml, with a lockout interval of 1 hour without a 4 hour volume limit, for 3 days. The mean attempted number of bolus infusions, and effective infused bolus volume for 3 days were compared in both groups. The adverse reactions in both groups were also recorded and compared.