DRUG DELIVERY DEVICE

A single-use auto-injector includes a housing and a dosing unit in at least part of the housing. The dosing unit includes a needle, a drug container with drug, a piston movable in the container, a first mechanical power supply for moving the piston to deliver the drug, an activation mechanism, and a mechanical escapement mechanism for controlling the movement of the piston. The auto-injector has a first state in which the needle is protected from needle damage or contamination, a second state in which the needle is ready to penetrate a human body, a third state in which the needle has penetrated the human body and is ready to dose, and a fourth state in which the needle is shielded to avoid unintended needle sticks. A second mechanical power supply is configured to shift state of the auto-injector from the third state to the fourth state.