Abstract Background: Long-term use of opioids has acute effects on homeostasis of the body. Discovering the impacts of opioids on hematological parameters of narcotics withdrawal and dependents blood may be helpful in recognizing the homeostasis condition of their body for the useful treatment. Methods: In this study a cross-sectional method was applied. The abusers of opium and heroin for more than two consecutive years were considered as opium and heroin dependent groups, respectively. The dependent people, who passed the 1-month withdrawal period, entered the study as opium and heroin withdrawal groups. In this study, hematological factors of heroin and opium dependent and withdrawal groups were investigated. Findings: The RBC count remained unchanged in all groups. The WBC count had a significant increase in opium dependent group but in heroin dependent group and withdrawal group there was no significant difference. HGB level had a significant increase only in opium and heroin withdrawal groups. The percentage of HCT had a significant increase in all groups. The MCV increased in heroin and opium dependent groups. MCH level increased significantly in heroin and opium withdrawal groups. MCHC level had a significant increase in all groups. Neutrophil and lymphocyte counts in heroin and opium addicted groups significantly decreased. Platelet, neutrophil and monocyte counts significantly increased in opium dependent group. Monocyte countshowed a significant reduction in heroin withdrawal group. Eosinophil count showed no difference in any of the groups. Conclusion: The current study indicated that not only the chronic and long-term use of opium and heroin, also withdrawal of addicted people could change hematological parameters related to human serum. Keywords: Hematological Factors, Serum, Addiction, Addiction Withdrawal, Heroin, Iran.