Background: Rosuvastatine, doxazosin, repaglinide and oxcarbazepin are therapeutic drugs available in the market for the treatment of different diseases. Potential to display antitumor activities has also been suggested. The aim of the current study was to evaluate their in vitro effects on some human transformed cell lines. Materials and Methods: Cytotoxicity of the four drugs was tested in MCF-7, HeLa and HepG2 cells by the neutral red assay method and also the effect of rosuvastatine and doxazosin against Ehrlich Ascities Carcinoma Cells (EACC) by trypan blue assay. Results: Rosuvastatine exerted the greatest cytotoxic effect against HepG2 cells with an $IC_{50}$ value of $58.7{pm}69.3$; in contrast doxazosin showed least activity with $IC_{50}=104.4{pm}115.7$. Repaglinide inhibited the growth of both HepG2 and HeLa cells with $IC_{50}$ values of $87.6{pm}117.5$ and $89.3{pm}119.5$, respectively. Oxcarbazepine showed a potent cytotoxicity against both HeLa ($IC_{50}=19.4{pm}43.9$) and MCF7 cancer cells (($IC_{50}=22{pm}35.7$).On the other hand the growth of EACC was completely inhibited by doxazosine (100% inhibition) while rosuvastatine had weak inhibitory activity (11.6%). Conclusions: The four tested drugs may have cytotoxic effects against hepatic, breast and cervical carcinoma cells; also doxazosine may inhibit the growth of endometrial cancer cells. Further investigations in animals are needed to confirm these results.