An osmotic system for delivering an agent is disclosed. The system comprises a wall surrounding a compartment and has a passageway through the wall for delivering agent from the compartment. The wall is formed of a material permeable to the passage of an external fluid and impermeable to the passage of agent. The compartment contains an agent that is soluble in the fluid and exhibits an osmotic pressure gradient across the wall against the fluid, or the compartment contains an agent that has limited solubility in the fluid and exhibits a limited osmotic pressure gradient across the wall against the fluid. The compartment also contains a suspending agent and a delivery member for increasing the amount of agent delivered from the system. The delivery member comprises a semipermeable film surrounding an osmotically effective compound and it is able to increase in volume over time. In operation, agent is delivered from the system through the passageway at a controlled rate by fluid being imbibed through the wall into the compartment to produce a solution or suspension containing agent, and for urging the member to increase in volume and fill the compartment, whereby agent is released at a rate controlled by the permeability of the wall, the osmotic pressure gradient across the wall, and the increase in volume of the member over a prolonged period of time.