This letter proposes a simple and novel method for mitigating inter-symbol interference (ISI) in molecular communication via diffusion (MCvD). In MCvD applications, the messenger molecules released from the transmitter need some time to reach the receiver. Therefore, the molecules absorbed at the beginning of a transmission interval can only belong to the previous transmissions. Therefore, if a receiver shifts its absorption interval, ISI can be potentially reduced. We find the optimal delay time that the receiver shifts its absorption interval both numerically and analytically to minimize the ISI in the channel. We demonstrate the improved performance of the proposed shift-τ method in molecular communication over conventional concentration shift keying modulation. The major benefits of the proposed method are its simplicity and applicability to many other schemes in the literature.