Abstract:This work describes the pharmacological activity of extracts of Papaver somniferum L., a poppy species. P. somniferum L. products are still considered as a unique source of drug for many diseases. The present study was designed to determine antiproliferative and cytotoxic effects of P. somniferum L. extracts on HeLa (Human Cervix Carcinoma), HT29 (Human Colorectal Adenocarcinoma), C6 (Rat Brain Tumor Cells), and Vero (African Green Monkey Kidney) cell lines. Alkaloid-rich extracts of P. somniferum L. exhibited antiproliferative effects on various cancer cell lines, especially at high concentrations. We assessed the ability of extracts of P. somniferum L. to give harm to the membrane of the cells. Results indicated that P. somniferum L. extracts destroy cellular membrane in tumor cell lines at high concentrations. Remarkably, the LDH test results disclosed that cytotoxicity of P. somniferum L. on cells was low at middle concentrations. This may indicate its cytostatic potential. The results of this study support the efficacy of P. somniferum L. extracts as an anticancer agent.