A wearable drug delivery device that can deliver a liquid drug stored in a container to a patient or user is provided. A soft needle or cannula can be placed in fluid communication with the liquid drug and can be coupled to a needle insertion component that provides access to the patient. A drive system of the drug delivery device can expel the liquid drug from the container to the patient through the soft needle or cannula. The wearable drug delivery device can include components for preventing backflow and eliminating air within the liquid drug. As a result, the comfort of the patient can be enhanced and correct drug dosages can be provided when using the drug delivery device.