Abstract: An apparatus includes a cartridge having a liquid drug reservoir configured to hold a liquid drug and a volatile liquid reservoir configured to hold a volatile liquid. The cartridge is configured so that vaporization of at least some of the volatile liquid creates a flow of the liquid drug out of the liquid drug reservoir. The apparatus also includes a flow sensor configured to monitor the flow of the liquid drug, a liquid valve configured to regulate the flow of the liquid drug, and an insertion unit configured to deliver the liquid drug to a person. The cartridge may also include a vaporized gas chamber configured to hold the gas. The gas in the vaporized gas chamber expands and pushes the liquid drug out of the liquid drug reservoir.