Background and aim: Carbon dioxide (Co2) is used during laparoscopy for producing pneumoperttoneum. Combination of this gas with irrigation fluid in the abdomen produces carbonic acid which creates two kinds of abdominal and referred pain to right shoulder. In the present research we have studied the effect of oral acetazolamide in reducing postoperative pain after laparoscopic cholecystectomy. Methods: This clinical trial was performed in 88 patients with cholelithiasis without any complication that were candidate for laparoscopic cholecystectomy. The patients devided randomly and equally in two groups. The experimental group received Acetazolamide (250mg orally 24 hours before surgery every 8 hours) and control group received placebo. Abdominal and shoulder pain measured using Mc Gill pain score by a person who was blind for both groups. Pain measurement was performed in four different times before and after the surgery discharge from recovery and 24 hours after surgery. Data were analyzed by using SPSS software. Results: We observed that mean pain scores was significantly higher in acetazolamide group compared to the placebo group 24 hours after the operation (P0.05). Conclusion: Although acetazolamide can reduce abdominal pain referred to right shoulder by reducing acidity in peritoneal irrigation fluid but this drug can increase abdominal pain in the site of surgery with damaged tissues by producing tissue acidosis (as a side effect of drug)
