Wearable automatic injection device and related methods of assembly and use

)isclosed herein is a wearable automatic injection device for providing an injection of a lerapeutic agent into a patient, the wearable automatic injection device comprising: a ousing comprising a contact portion securable to the patient; an injection assembly moveably isposed in the housing holding an injection needle for insertion into the patient, the injection ssembly movable between a retracted position in which the injection needle does not rotrude outside the housing and an extended position in which the injection needle protrudes utside the housing; and a prefilled container assembly disposed in the housing for holding le therapeutic agent, the prefilled container assembly comprising a barrel with a sealed distal nd, the barrel having a first stopper, a second stopper spaced from and movable relative to le first stopper, and a dispensing member coupled to a distal portion of the second stopper nd configured to engage the first stopper, wherein the dispensing member is in fluid ommunication with the injection needle.