Cellular and molecular mechanisms of the development of drug dependence are similar to those of learning process and this fact allows a great number of researches to call dependence “a pathology of memory and learning”. Earlier when the changes of hippocampal synaptic plasticity resulting from prolonged morphine consumption were studied we’ve shown that facilitation of mossy fiber long-term potentiation (LTP) was observed during the development and early stages of chronic dependence with peak of LTP facilitation at 8-10 days of morphine consumption. We’ve also shown that immunomodulator Myelopide significantly increased the time necessary for the formation of drug dependence. In present study we analyzed the changes in hippocampal synaptic plasticity in rats that received Myelopide injections during the development of chronic opiate dependence (1st and 10th day of oral morphine consumption). It was found that in this case LTP facilitation manifested not earlier than at 25-28th day of drug consumption and this “time shift’ in characteristics of synaptic plasticity correspondent to the increase in time necessary for the formation of dependence. Thus the influence of Myelopide on modification of synaptic plasticity resulting from the prolonged morphine consumption may be one of the mechanisms included in the inhibition of the development of chronic opiate dependence by this medicine.