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Background: Morphine is one of the derivations of opium alkaloids. Contradictory reports exist on hyperglycemic and hypoglycemic effects of morphine. The aim of this study was to evaluate the role of opioid receptors involved in blood glucose changes in morphine-treated Balb/c mice. Materials and Methods: This experimental study was carried out on 8 groups of male Balb/c mice (n=6), including group1(morphine), group 2 (naloxone (morphine antagonist) + morphine), group 3 (naltrindole ( receptor antagonist) + morphine), group 4 (norbinaltorphimine ( receptor antagonist) + morphine), group 5 (CTOP ( receptor antagonist) + morphine), group 6 (saline), group 7 (saline + saline), and group 8 (saline + morphine). Blood samples were obtained from retro-orbital sinus at 0, 1, 2, and 3 hours after injection. Blood glucose level was measured by enzymatic technique. Data were analyzed by SPSS software. Results: The application of morphine resulted in significant hypoglycemia in comparison with the control group which was significantly compensated by naloxone compared to the morphine group. The application of naltrindole could significantly inhibit hypoglycemia induced by morphine compared to the control group, whereas norbinaltorphimine and CTOP failed to do so. Conclusion: Since naltrindole could compensate for hypoglycemia due to morphine, hypoglycemia caused by morphine is likely to be mediated by opioid receptors