Injector device comprising: (a) an injector body that includes a front assembly and a rear assembly that cooperate to define an interior, including the front assembly a forward housing, a needle holder (111) that is movable relative to the housing towards between a rearward position and a forward position, a first shock absorber (192) disposed on a rearward face of the forward housing and a second shock absorber (196) disposed on a rear part of the needle holder (111), where the needle holder it is coupled to the first shock absorber (192) when it is in the forward position, and the syringe holder (111) is separated from the first shock absorber (192) when it is in the rearward position； (b) a syringe (180) configured to engage the syringe holder (111) for movement with it, including the syringe (180) a vial, a needle and a plunger, the needle extending from a first end of the vial and extending the plunger from a second end of the vial, at least a portion of the vial being coupled to the second buffer (196), the vial being configured to contain a common volume of one or the other of at least two different medication formulation without modification of the injector device, a first of the two different drug formulations having a first viscosity and a second of the two different drug formulations having a second viscosity that is different from the first viscosity； and (c) an injection assembly (140) disposed within the interior of the injector body, the injection assembly being configured to dispense the medication formulation contained by the syringe (180), the injection assembly including a piston (141) actuated by a constant force spring (149), where the release of the constant force spring (149) drives the needle holder (111) from the rearward position to the forward position until the needle holder (111) engages the first damper (192), and wherein the constant force spring (149) drives the plunger inside the syringe vial after the syringe holder (111) is in the
