An automatic drug delivery device comprising: a housing; a skin sensor element coupled to the housing and movable relative to the housing, wherein the skin sensor element is biased into a front position relative to the housing and is movable to a rear position relative to the housing when the skin sensor element is pressed against an injection site; a needle assembly (9, 11) comprising a hypodermic needle, the hypodermic needle extending outside of the housing when the device is in a needle insertion position; a drug delivery mechanism comprising a first stored energy source, within the housing, a drive member positioned between the first stored energy source and the needle assembly, wherein the drive member comprises a resilient portion and engages the needle assembly to drive the needle assembly to the needle insertion position; wherein the drug delivery mechanism is released when the skin sensor element is moved from the front position towards the rear position and wherein the first stored energy source is arranged to expand along an axis that is offset from an axis of travel of the needle assembly in use, and wherein in operation the drug delivery mechanism moves the needle assembly from an initial position to the needle insertion position, a needle retraction mechanism configured to withdraw the hypodermic needle into the housing when the needle retraction mechanism is released, wherein the needle retraction mechanism is coupled to the skin sensor element such that when the skin sensor element is moved from the rear position towards the front position, and the needle is in the needle insertion position, the needle retraction mechanism is released; and wherein the resilient portion is deflected to disengage the drive member from the needle assembly when the needle assembly reaches the needle insertion position and the skin sensor element is moved from the rear position to the front position, so as to uncouple the first stored energy source from the needle assembly. a housing; a skin sensor element coupled to the housing and movable relative to the housing, wherein the skin sensor element is biased into a front position relative to the housing and is movable to a rear position relative to the housing when the skin sensor element is pressed against an injection site; a needle assembly (9, 11) comprising a hypodermic needle, the hypodermic needle extending outside of the housing when the device is in a needle insertion position; a drug delivery mechanism comprising a first stored energy source, within the housing, a drive member positioned between the first stored energy source and the needle assembly, wherein the drive member comprises a resilient portion and engages the needle assembly to drive the needle assembly to the needle insertion position; wherein the drug delivery mechanism is released when the skin sensor element is moved from the front position towards the rear position and wherein the first stored energy source is arranged to expand along an axis that is offset from an axis of travel of the needle assembly in use, and wherein in operation the drug delivery mechanism moves the needle assembly from an initial position to the needle insertion position, a needle retraction mechanism configured to withdraw the hypodermic needle into the housing when the needle retraction mechanism is released, wherein the needle retraction mechanism is coupled to the skin sensor element such that when the skin sensor element is moved from the rear position towards the front position, and the needle is in the needle insertion position, the needle retraction mechanism is released; and wherein the resilient portion is deflected to disengage the drive member from the needle assembly when the needle assembly reaches the needle insertion position and the skin sensor element is moved from the rear position to the front position, so as to uncouple the first stored energy source from the needle assembly.