An osmotic system for delivering a beneficial 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 means for increasing the amount of agent delivered from the system. The means comprises a film surrounding an osmagent with the film formed of a material permeable to fluid, impermeable to osmagent and movable from an initial to an expanded state. 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 imbibition by the means causing it to concentrate the solution or suspension, expand and fill the compartment, whereby agent is released at a rate controlled by the permeability of the wall, the oosmotic pressure gradient across the wall, and the rate of imbibition and expansion of the means over a prolonged period of time.