In this double blind study, we will select two groups of 150 renal colic patients; with 18-69 years old age and Pain score, equal or more than 40 or 4 in VAS or NRS system, respectively; according to Balanced Block Randomization method and inclusion and exclusion criteria. Inclusion criteria include : age 18-69 years old Pain score equal or more than 40 or 4 in VAS or NRS system, respectively; and Exclusion criteria include: Pyelonephritis or fever equal or more than 38 degree centigrade, History of addiction or opioid allergy, History of cardiovascular disease (function class 3-4 or decompensated CHF or uncontrolled hypertension) , History of active hepatobiliary disorders Hemodinamically unstable patients (BP below 90mmHg or MAP decreased more than 30% baseline), Pregnancy and Breast feeding and History of CVA in last 2 years. Group A will receive 1 cc saline as placebo and group B will receive 1 CC of low dose naloxone (0.04 mg) intravenously. 5 minutes later, both groups will receive 2.5 mg morphine sulfate intravenously. Then we will fallow the patients according to their pain score and complications every 15 minutes for about 90 min. If the pain score does not diminish below 4, we will administer other doses of morphine (max dose: 10 milligram). If despite the Morphine administration (max dose: 10 mg), pain score remains more than the mentioned threshold, the patient will exclude from the study but his pain management will continue. During this study, we will assess if naloxone could diminish the pain score and total dose of morphine administration in according to lower complications than morphine and placebo in renal colic patients.