Background: Experiments have shown that opioid drugs abuse during pregnancy can cause a delay in the development of the placenta. In mammals, the placenta is the most important channel for the exchange of Materialss between the maternal and fetal bloods. The present study investigates the time-dependent effect of the addiction duration of maternal morphine consumption during pregnancy.Materials and Methods: Female wistar rats with an average weight of 170 to 200 grams were used in this experimental research. Experimental groups received morphine (0.05 mg/ml of drinking water) after one night coupling with male rats for mating. On 9th, 10th, 14th days of pregnancy, pregnant animals were killed, placentas removed and fixed. The cells of the placentas layers were calculated by light microscope, MOTIC and SPSS software.Results: The thickness of the maternal portion of the placenta increases with morphine abuse in all three experimental groups compared to the control groups with a time-dependent manner. On the other hand, the findings of the present study, aligned with the body of research concerning the time-dependent effect of morphine consumption, revealed a significant reduction in the thickness of the fetal portion of the placenta in the experimental groups.Conclusion: Overall, these results show that most of the negative effects of oral morphine consumption by pregnant women are time-dependent, and the severity of the delay in the development of the placental layers, depending on the duration of morphine consumption is more evident. In a general conclusion, it can be stated that the time-dependent effects of oral morphine consumption, can cause a delay in the natural development of cytotrophoblast and syncytotrophoblast cells of the placental layers in rats.