Exemplary embodiments provide wearable automatic injection devices for subcutaneously injecting a therapeutic agent into a patient's body at controlled rates, for example, in a single bolus. Exemplary embodiments provide methods for assembling wearable automatic injection devices for subcutaneously injecting a therapeutic agent into a patient's body at controlled rates. Exemplary embodiments provide methods for using wearable automatic injection devices for subcutaneously injecting a therapeutic agent into a patient's body at controlled rates.