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Background: Considering the previous studies on the harmful effects of opioids on some body organs, determining the histological changes of liver due to heroin, as the most used opium in Iran, seems to be necessary.
 Materials and methods: In this experimental study, a total of 30 mice were divided into three control and two experimental groups. Having depended to heroine (50mg/kg IP for 3 days, twice daily), different experimental groups of dependant mice were divided into two groups. One of which received heroin 5 mg/kg IP and the other 5 mg /ml, IP twice daily for a period of 40 days. Then, the mice were euthanized and by removing the livers, they were sectioned and stained with H&E and the histological structures of liver were studied.
Results: There were no histological differences between control groups, however, the experimental and control groups showed some differences such as hyperemia in central veins, presence of inflammatory cells in portal space and its relative parenchyma, irregularity in hepatocyte, enlarging the sinusoids and nuclei and finally repairing changes in liver.
Conclusion: With respect to the observed histological changes, liver's histological changes should be kept in mind as one of the dangerous effects of opioids among addicted Iranian subjects.