Optimizing fluid transport in pipelines is essential to increase operational efficiency and reduce associated costs. The high friction characteristic of these flows leads to significant energy losses and substantially raises operating expenses. In this context, the use of polymers as drag-reducing agents emerges as a promising solution, capable of increasing throughput and lowering energy consumption. Predicting the drag-reduction potential is crucial not only during the design phase of new pipelines-sized to meet specific demands-but also in the operation of existing systems. Such predictions guide the determination of the frequency and dosage of polymer injections, thereby optimizing system performance. This work aims to analyze, via numerical simulation, the performance of friction-reduction factors derived from single-phase flows when applied to pipelines operating under two-phase flow conditions, in slug pattern, to predict drag reduction. Various flow scenarios were considered to evaluate the effects of polymer addition on pressure-drop reduction as well as on slug-flow statistics - such as slug length, its propagation velocity, and frequency. Good agreement was obtained with experimental measurements of these quantities. It was shown that polymer injection significantly reduces pressure loss and, consequently, energy consumption. The results underscore the potential of employing the Two-Fluid Model augmented with single-phase drag-reduction factors to predict the performance of polymer additives in complex two-phase flows.