Background/Objectives: This study investigates the role of peripheral opioid receptors in modulating pain outside the central nervous system. Methods: The first experiment aimed to establish a dose-effect relationship for intraplantar morphine administration in a rat model of carrageenan-induced inflammation by testing successive doses after the carrageenan injection. Additionally, the second experiment assessed whether a 5 mg/kg dose of morphine has central nervous system effects by comparing its effects with 5 mg/kg and 10 mg/kg doses given intraperitoneally. Results: In the first part we observed that lower doses (2.5 mg/kg) did not significantly affect paw withdrawal latency after thermal stimulation, while higher doses (5 mg/kg and 10 mg/kg) resulted in significant increases, suggesting that maximum receptor activation occurs at 5 mg/kg. However, the 20 mg/kg dose exhibited central nervous system effects, indicating systemic absorption. The second part compared intraplantarly and intraperitoneally administered morphine, finding that while the intraplantar 5 mg/kg dose provided a significant analgesic effect, the same dose given intraperitoneally did not produce similar results, reinforcing the hypothesis that local administration targets peripheral receptors. Conclusions: Overall, the findings indicate that morphine's analgesic effect at lower doses is primarily mediated by peripheral opioid receptors, with systemic effects becoming evident at higher doses. This study aligns with existing literature emphasizing the potential for peripheral opioid receptor activation to alleviate inflammatory pain with minimized central effects