Given the controversies regarding the potential role of metformin against tumour progression, the effect of metformin against breast, cervical, and ovarian tumour cell lines was examined followed by in vivo assessment of metformin on tumour growth using xenograft breast cancer models. Significant inhibitory impact of metformin was found on MCF-7, HeLa, and SKOV-3 cells, suggesting an antiproliferative property of metformin against breast, cervical, and ovarian tumour cells, respectively, with the breast tumour cells, MCF-7, being the most responsivenessresponsive.