A combination of a wearable medical device in contact with a user's body for administering drug therapy to the user and a wearable host device adapted to communicate with the medical device, the medical device comprising: a microcontroller electrically coupled to a pump mechanism, a first transceiver, and a power supply system, wherein: the microcontroller commands the pump mechanism to administer a drug to the user; the first transceiver comprises a first electrode capacitively coupled to an outer surface of the user's skin and a second electrode coupled to a reference potential, wherein the impedance between the second electrode and the reference potential is higher than the impedance between the first electrode and the outer surface of the user's skin, and wherein the second electrode provides an oscillating potential to cause a displacement current in the user's body, and communicates with a host device on or near the user's body via a personal area network that transmits data across the user's body by modulating the displacement current, wherein said host device monitors or controls the medical device; and the power supply system selectively provides power to the microcontroller, pump mechanism and first transceiver supplied from an energy harvesting component that harvests energy from the user's body, the host device comprising a second transceiver capacitively coupled to the first transceiver and comprising a third electrode capacitively coupled to an outer surface of the user's skin and a fourth electrode, wherein a first capacitor C ist provided to connect the first transceiver to ground, a second capacitor D is provided to connect the second transceiver to ground and a third capacitor G is provided to connect the user's skin to ground. a microcontroller electrically coupled to a pump mechanism, a first transceiver, and a power supply system, wherein: the microcontroller commands the pump mechanism to administer a drug to the user; the first transceiver comprises a first electrode capacitively coupled to an outer surface of the user's skin and a second electrode coupled to a reference potential, wherein the impedance between the second electrode and the reference potential is higher than the impedance between the first electrode and the outer surface of the user's skin, and wherein the second electrode provides an oscillating potential to cause a displacement current in the user's body, and communicates with a host device on or near the user's body via a personal area network that transmits data across the user's body by modulating the displacement current, wherein said host device monitors or controls the medical device; and the power supply system selectively provides power to the microcontroller, pump mechanism and first transceiver supplied from an energy harvesting component that harvests energy from the user's body, the microcontroller commands the pump mechanism to administer a drug to the user; the first transceiver comprises a first electrode capacitively coupled to an outer surface of the user's skin and a second electrode coupled to a reference potential, wherein the impedance between the second electrode and the reference potential is higher than the impedance between the first electrode and the outer surface of the user's skin, and wherein the second electrode provides an oscillating potential to cause a displacement current in the user's body, and communicates with a host device on or near the user's body via a personal area network that transmits data across the user's body by modulating the displacement current, wherein said host device monitors or controls the medical device; and the power supply system selectively provides power to the microcontroller, pump mechanism and first transceiver supplied from an energy harvesting component that harvests energy from the user's body, the host device comprising a second transceiver capacitively coupled to the first transceiver and comprising a third electrode capacitively coupled to an outer surface of the user's skin and a fourth electrode, wherein a first capacitor C ist provided to connect the first transceiver to ground, a second capacitor D is provided to connect the second transceiver to ground and a third capacitor G is provided to connect the user's skin to ground. a second transceiver capacitively coupled to the first transceiver and comprising a third electrode capacitively coupled to an outer surface of the user's skin and a fourth electrode, wherein a first capacitor C ist provided to connect the first transceiver to ground, a second capacitor D is provided to connect the second transceiver to ground and a third capacitor G is provided to connect the user's skin to ground.