Objective: Comparing the effect of melatonin, clonidine or gabapentin on reducing the preoperative anxiety and postoperative pain in patients undergoing laparoscopic cholecystectomy. Patients referred to Shariati Hospital in 1393 for laparoscopic cholecystectomy who did not did not have a history of congenital heart diseases, heart valve diseases, liver or kidney diseases, psychological disorders, opioid addiction, uncontrolled hypertension, and those without with verbal or communication difficulties will be included in the study. In a randomized double-blind placebo-controlled clinical study, 88 patients undergoing laparoscopic cholecystectomy under general anesthesia will be enrolled and randomly assigned to one of the four study groups: clonidine (C), melatonin (M), gabapentin (G), or placebo (P). 120 minutes before inducing anesthesia, patients will be administered oral clonidine (0.2 mg), melatonin (6 mg), gabapentin (600 mg), or placebo, respectively. In order to alleviate the pain, morphine will be administered using the PCA instrument. Preoperative anxiety, changes in the vital signs after induction of anesthesia, total dosage of the intraoperatively administered opioid, Bispectral index (BIS), morphine dosage within 24 h of the operation, the first time of requesting morphine post-operation, and postoperative nausea and vomiting (PONV) will be recorded and compared for all patients. The level of pain will also be accessed and recorded using a 10-score visual analogue scale (VAS) 1 h, 2 h, 6 h, 12 h, and 24 h after the surgery.