An injection device for injecting medicament in a patient includes a syringe coupled to a housing and radially retained by a retaining rib. A needle guard is slideably coupled to the housing and spring biased in a distal direction by a return spring. A ram is slideably coupled to the housing and spring biased in the distal direction by a main spring. An initial position is defined by a retaining arm being disposed in the longitudinal path of the ram preventing firing. A released position is defined by the retaining arm being clear from the longitudinal path of the ram allowing the ram to extend distally. A locked position is defined by the retaining arm being disposed in the longitudinal path of the ram and a lock arm of the ram being disposed in the longitudinal path of the needle guard preventing the needle guard from being retracted.
