The present invention relates to a drug delivery device and in particular to temperature sensitive labelling of such devices. The drug delivery device is designed for dispensing of a dose of a medicinal product and comprises a housing, and a drive mechanism comprising an axially displaceable piston rod to act on a piston of a cartridge containing the medicinal product to be dispensed. The device is further provided with a protective cover arranged across a functional component of the device, and adapted to irreversibly change at least one of its visually perceptible properties in response to the ambient temperature rising above or dropping below at least one predefined threshold.