An apparatus includes a housing, an actuator, a lock mechanism, and a medicament container. The lock mechanism selectively engages a portion of the housing such that (1) the lock mechanism is maintained in a substantially fixed position when the housing is in a first orientation and (2) the lock mechanism is removable from the housing when the housing is in a second orientation. The medicament container is moved in a proximal direction when the lock mechanism is removed from the housing to mix a first medicament portion contained within the medicament container with a second medicament portion contained within the medicament container. The actuator can be moved from a first position to a second position when the lock mechanism is removed from the housing to release energy stored within an energy storage member such that the medicament container is moved in a distal direction.