The nature of molecular transmitter imposes some limitations on the molecule production process and its storage. As these molecules act the role of the information carriers, their limitation affect the transmission process and the system performance considerably. In this paper, we focus on these limitations at the transmitter, the limited production rate and finite storage capacity. We consider a time-slotted communication where the transmitter opens its outlet and releases the stored molecules for a time duration to send bit “1” and remains silent to send bit “0”. By changing the duration molecules are released, we propose an adaptive pulse-width modulation. The objective is to find the optimal transmission pulse-widths to minimize the probability of error. We characterize the properties of the optimal pulse-widths and use them to derive upper and lower bounds on the performance.