The influence of long-term opioid administration on hormonal levels is not well characterized in the literature. We previously showed that intrathecal opioid therapy significantly influences the homeostasis of immune and endocrine systems. Other authors confirmed that exogenous and endogenous opioids induce this effect. They have a cytokine-like behavior and may function as neurotransmitters, neuromodulators or hormones, as concerning their synthesis, storage and release.