We introduce a full duplex multiuser multiple-input multiple-output (FD MU-MIMO) system, and consider the total throughput maximization problem under a sum power constraint in the downlink (DL) channel and per-user power constraints in the uplink (UL) channel. Due to the nature of asymmetric DL/UL capacity, a trivial method to this problem is to optimize the DL and UL channels sequentially. However, when the self-interference (SI) is large, the sum rate of the UL channel in this sequential design is dramatically degraded. Herein, a joint design is proposed, in which the DL and UL channels are optimized simultaneously. Since the objective function of the throughput maximization problem is non-convex, it is difficult to find the optimal solution. Thus, we propose a joint iterative algorithm to find a suboptimal design, using a local optimization strategy. Simulation results demonstrate that the iterative joint design outperforms the sequential design, and the FD MU-MIMO system is superior to the conventional half duplex (HD) system in terms of the total system throughput when the SI is sufficiently small. This makes the FD MU-MIMO techniques promising for small cell deployments where the transmit power is relatively small.