An automatic medication injection device comprising: a housing; a syringe filled with medication and including a needle and a plunger; a driver shiftable proximally in said housing along a track from a ready position to a plunged position, said driver and said track and said plunger being complementarily configured for said driver, when shifted from said ready position to said plunged position, to advance said plunger to move said syringe proximally from a start position, at which said needle is disposed within said housing, to an injecting position, at which said needle projects external to said housing, and to advance the plunger to expel medication from the syringe through said needle, and to disengage from said plunger to permit axial movement of said driver relative to said plunger; a retractor (190, 200, 230) having an opening (192, 202, 232) in which said syringe extends, said retractor shiftable distally within said housing from a ready position to a retraction position to withdraw said syringe from said injecting position to a retracted position at which said needle is disposed within said housing; a blocking member having an opening in which said syringe extends, said blocking member rotatable within said housing from a first rotational orientation to a second rotational orientation, said blocking member complementarily configured with said retractor (190, 200, 230) to block movement of said retractor from said ready position to said retraction position when disposed in said first rotational orientation, and to permit movement of said retractor from said ready position to said retraction position when disposed in said second rotational orientation; at least one biasing member preloaded to urge said driver proximally and to urge said retractor (190, 200, 230) distally; a trigger actuatable to allow said at least one biasing member to move said driver from said ready position to said plunged position; and said driver and said blocking member having a complementary camming configuration (124, 304) for said blocking member to be forcibly rotated automatically from said first rotational orientation to said second rotational orientation when said driver shifts from said ready position to said plunged position. a housing; a syringe filled with medication and including a needle and a plunger; a driver shiftable proximally in said housing along a track from a ready position to a plunged position, said driver and said track and said plunger being complementarily configured for said driver, when shifted from said ready position to said plunged position, to advance said plunger to move said syringe proximally from a start position, at which said needle is disposed within said housing, to an injecting position, at which said needle projects external to said housing, and to advance the plunger to expel medication from the syringe through said needle, and to disengage from said plunger to permit axial movement of said driver relative to said plunger; a retractor (190, 200, 230) having an opening (192, 202, 232) in which said syringe extends, said retractor shiftable distally within said housing from a ready position to a retraction position to withdraw said syringe from said injecting position to a retracted position at which said needle is disposed within said housing; a blocking member having an opening in which said syringe extends, said blocking member rotatable within said housing from a first rotational orientation to a second rotational orientation, said blocking member complementarily configured with said retractor (190, 200, 230) to block movement of said retractor from said ready position to said retraction position when disposed in said first rotational orientation, and to permit movement of said retractor from said ready position to said retraction position when disposed in said second rotational orientation; at least one biasing member preloaded to urge said driver proximally and to urge said retractor (190, 200, 230) distally; a trigger actuatable to allow said at least one biasing member to move said driver from said ready position to said plunged position; and said driver and said blocking member having a complementary camming configuration (124, 304) for said blocking member to be forcibly rotated automatically from said first rotational orientation to said second rotational orientation when said driver shifts from said ready position to said plunged position.