There provided a drug delivery device adapted for providing a plurality of discrete doses of a medicament including a disposable delivery unit (2) adapted to be worn by a user, comprising a reservoir (10b) for holding a medicament to be delivered, an injection member (22) adapted for trans-dermal drug delivery, and a pump (12) adapted for pumping the medicament to be delivered from the reservoir (10b) to the injection member (22); and a separate reusable base unit (4) comprising a drive module for driving the pump (12). The pump in the disposable delivery unit is activated to deliver a dose of the medicament by bringing the base unit temporarily into communication with the delivery unit.