Breast cancer is the most frequently diagnosed cancer among women worldwide, underscoring the critical need for developing innovative strategies to control tumor growth. Current research emphasizes the significance of combination therapies in enhancing efficacy, reducing toxicity, and mitigating drug resistance. One particularly promising approach is drug repurposing, where clinically approved drugs are identified for new therapeutic applications. Aberrant metabolic activity, a hallmark of cancer, contributes significantly to cellular immortality and sustained proliferative activity. Thus, compounds that can modulate energy metabolism present a potent strategy for controlling tumor growth. Among such compounds, metformin (Met) and alpha-lipoic acid (α-LA) have well-documented effects on cellular metabolism and are widely used to treat various pathologies. In our study, we investigated the effects of Met and α-LA on the viability of the breast tumor cell line 4T1. The cells were treated with different concentrations of Met (1, 5, and 10 mM) and α-LA (0.05 and 0.1 mM), both individually and in combination. Cell viability was then assessed using methyl thiazolyl tetrazolium (MTT) assays. Our findings revealed a statistically significant decrease in cell viability when treated with both Met and α-LA simultaneously, compared to individual treatments. This indicates a strong synergistic effect, as confirmed by a positive synergy score for all four algorithms analyzed in SynergyFinder. These results suggest that the combination of Met and α-LA exerts a potent antitumor activity, highlighting a promising therapeutic avenue for breast cancer treatment. The implications of this study could open new doors for leveraging existing drugs in innovative ways to combat one of the most challenging diseases worldwide.