A wearable drug delivery device includes a housing, a needle assembly at least partially disposed in the housing, and a drive assembly at least partially disposed in the housing and coupled to the needle assembly. The needle assembly includes a needle or cannula and a sterile barrier disposed proximal to the needle or cannula in a first configuration where the sterile barrier is intact. The drive assembly includes a container that contains a medicament to be administered, a first plunger disposed in the container, and a drive mechanism that forces the first plunger to urge the medicament through the container. Upon engaging the drive mechanism, the needle or cannula and the sterile barrier move relative to each other from the first configuration to a second configuration where the needle or cannula breaks the sterile barrier, thereby allowing the medicament to be administered via the needle or cannula.