A drive mechanism of a drug delivery device and a respective drug delivery device for setting and dispensing of a dose of a medicament are presented, where the drive mechanism has an elongated housing extending in an axial direction, a piston rod to operably engage with a piston of a cartridge containing the medicament, a dosing arrangement manually and axially displaceable relative to the housing for setting and dispensing of the dose, and an accessory drive operably engaged with the piston rod to support a manually operated dose dispensing displacement of the dosing arrangement.