Drug delivery assembly comprising: micro needles (151) capable of transdermal fluid delivery, a reservoir (13) containing the drug (14) and fluidly coupled to the micro needles, a plunger (132) coupled to the reservoir and operable to expel the drug from the reservoir, a housing (11) arranged to receive the reservoir, an actuation member (12) moveable relative to the housing (11), means (19) for storing energy, first retention means (17) configured for maintaining the reservoir (13) in a fixed position relative to the housing (11), and second retention means (18) configured for maintaining the plunger (132) in a fixed position relative to the reservoir (13). The first and second retention means are configured to change state in sequence, which releases respectively (A) the reservoir (13) from the housing (11) and (B) the plunger (132) from the reservoir (13). The means (19) for storing energy are operably coupled to the plunger (132) to provide a force on the plunger for moving the micro needles (151) against the skin upon the change of state (A) of the first retention means, as well as for moving the plunger to expel the drug (14) from the reservoir upon the change of state (B) of the second retention means.
