This paper investigates the effect of demand side management (DSM) program in distribution network on network losses and loading margin. The composite load model comprising constant impedance, constant current, constant power and induction motor loads is used to model the loads in the network. This enables a more accurate analysis of the changes in load flow and network loadability limit after applying a DSM program across all the buses in a distribution network with distributed generation. The applied DSM programme aims at maintaining as close to self-sufficient operation of the network as possible, by adjusting flexible demand in the network to the volatile distributed generation, and minimizing its reliance on the upstream network. The analysis shows how shifting different load components (namely constant impedance load or induction motors), and reconnecting them at different times following a DSM action (the so called load payback) affect the network performance. The network used in this paper is a modified IEEE 33 bus distribution network