Combination of Cannabidiol with Cisplatin or Paclitaxel Analysis Using the Chou–Talalay Method and Chemo-Sensitization Evaluation in Platinum-Resistant Ovarian Cancer Cells

Background/Objectives: Cannabidiol (CBD) is known for its anti-cancer properties in preclinical models and is increasingly used alongside conventional chemotherapy in cancer treatment. This study aims to evaluate the anti-cancer activity of CBD from Lebanese Cannabis sativa as a monotherapy and in combination with cisplatin or paclitaxel on human ovarian adenocarcinoma cells. Methods: Cytotoxicity of CBD was tested on OVCAR-3 and SK-OV-3 cell lines using the MTS assay. The Chou–Talalay method and CompuSyn software were used to determine the combination indices (CIs) for predicting interactions between CBD and chemotherapeutic agents. CBD showed dose-dependent tumor growth inhibition at 72 h with comparable IC50 values for both cell lines. Results: The combination of CBD with cisplatin or paclitaxel showed significant antagonistic interaction in SK-OV-3 cells (CI > 1), but mild synergism (CI < 1) at high growth inhibition rates (95% and 97%) was observed in SK-OV-3 cells with CBD/cisplatin. Pure antagonism was found in OVCAR-3 cells with CBD/cisplatin. Priming SK-OV-3 cells with CBD reduced the IC50 values of both drugs significantly, with a similar effect seen when cells were primed with cisplatin or paclitaxel before CBD treatment. Conclusions: Integrating CBD with chemotherapy could improve cancer therapy and address drug resistance. Sequential administration of CBD and chemotherapeutic agents is more beneficial than simultaneous administration. Further in vivo studies are necessary to validate these findings and understand CBD’s interactions with other drugs fully.