A single-use auto-injector for injection of a dosage of a drug into a human body, comprising: - a housing, and - a dosing unit arranged in at least part of the housing, the dosing unit comprising: - a needle, - a drug container comprising the drug, - a plunger movable in the container, - a first mechanical power supply for supplying a first mechanical force for moving the plunger via a shaft to deliver a drug to the human body, - an activation mechanism configured to release the first mechanical power of the first mechanical power supply, and - a mechanical escapement mechanism for controlling the movement of the plunger via the shaft, wherein the auto-injector comprises a second mechanical power supply for supplying a second mechanical force, the auto-injector having: - 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 the human body for dosing the drug, - 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, wherein the second mechanical power supply is configured to shift state of the auto-injector from the third state to the fourth state by releasing the second mechanical power. - a housing, and - a dosing unit arranged in at least part of the housing, the dosing unit comprising: - a needle, - a drug container comprising the drug, - a plunger movable in the container, - a first mechanical power supply for supplying a first mechanical force for moving the plunger via a shaft to deliver a drug to the human body, - an activation mechanism configured to release the first mechanical power of the first mechanical power supply, and - a mechanical escapement mechanism for controlling the movement of the plunger via the shaft, wherein the auto-injector comprises a second mechanical power supply for supplying a second mechanical force, the auto-injector having: - 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 the human body for dosing the drug, - 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, wherein the second mechanical power supply is configured to shift state of the auto-injector from the third state to the fourth state by releasing the second mechanical power. - a needle, - a drug container comprising the drug, - a plunger movable in the container, - a first mechanical power supply for supplying a first mechanical force for moving the plunger via a shaft to deliver a drug to the human body, - an activation mechanism configured to release the first mechanical power of the first mechanical power supply, and - a mechanical escapement mechanism for controlling the movement of the plunger via the shaft, - 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 the human body for dosing the drug, - 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,