The invention provides a drive mechanism for an autoinjector, configured to be coupled to a drug containing portion to form a complete autoinjector, the drive mechanism comprising: a housing (20); a drive means coupled to the housing, the drive means comprising a resilient member (22); a retaining means coupled to the housing, the retaining means (60) engaging the drive means in a first position to retain the resilient member in a deformed condition, and releasing the drive means in a second position; and a coupling means (24) for coupling with a drug containing portion (10). The drug containing portion retains the drive means in a second deformed condition when the retaining means is in the second position, the drive means storing enough energy in the second deformed condition to drive needle insertion and/or drug delivery.