In this letter, a novel pre-equalization method in the context of molecular communication via diffusion (MCvD) is proposed. Our method is based on the emission of two types of messenger molecules (MMs) from the transmitter in order to mitigate the high intersymbol interference (ISI), which critically hinders the performance of any MCvD system. In this approach, the difference between the number of received molecules of each MM type is considered as the actual signal at the receiver side. We model the underlying diffusion channel, and conduct an analysis on the error performance of the proposed method. We compare the proposed method with other modulation and ISI mitigation techniques in the literature, such as concentration shift keying, molecular shift keying, molecular concentration shift keying, and minimum mean squared equalization. Simulation results show that, by tuning the delay value between the emissions of the two MM types and their respective molecule counts, the proposed pre-equalization method outperforms the aforementioned methods and reduces the bit error rate of the MCvD system significantly.