A drug delivery system, comprising: - a housing, - a drug-filled cartridge or means for receiving a drug-filled cartridge, the cartridge comprising an axially displaceable piston and a distal outlet portion, - drug expelling means comprising: - dose setting means allowing a user to set a dose of drug to be expelled, - an axially displaceable piston rod adapted to move the piston of a cartridge in a distal direction to thereby expel drug from the cartridge, and - a first rotational member adapted to rotate relative to the housing corresponding to a set and/or expelled dose and comprising a first force transmitting surface, - a second rotational member adapted to rotate relative to the housing corresponding to a set and/or expelled dose and comprising a second force transmitting surface, - wherein at least portions of the first and second force transmitting surfaces are adapted to engage each other during setting and/or expelling of a dose, and - wherein the first rotational member comprises a magnet producing a magnetic spatial field which varies corresponding to the rotational movement of the first rotational member, characterized in that - wherein the first rotational member is fully formed from a polymeric material containing magnetic particles, the polymeric material having been magnetized to provide a magnet producing the magnetic spatial field. - a housing, - a drug-filled cartridge or means for receiving a drug-filled cartridge, the cartridge comprising an axially displaceable piston and a distal outlet portion, - drug expelling means comprising: - dose setting means allowing a user to set a dose of drug to be expelled, - an axially displaceable piston rod adapted to move the piston of a cartridge in a distal direction to thereby expel drug from the cartridge, and - a first rotational member adapted to rotate relative to the housing corresponding to a set and/or expelled dose and comprising a first force transmitting surface, - a second rotational member adapted to rotate relative to the housing corresponding to a set and/or expelled dose and comprising a second force transmitting surface, - dose setting means allowing a user to set a dose of drug to be expelled, - an axially displaceable piston rod adapted to move the piston of a cartridge in a distal direction to thereby expel drug from the cartridge, and - a first rotational member adapted to rotate relative to the housing corresponding to a set and/or expelled dose and comprising a first force transmitting surface, - a second rotational member adapted to rotate relative to the housing corresponding to a set and/or expelled dose and comprising a second force transmitting surface, - wherein at least portions of the first and second force transmitting surfaces are adapted to engage each other during setting and/or expelling of a dose, and - wherein the first rotational member comprises a magnet producing a magnetic spatial field which varies corresponding to the rotational movement of the first rotational member, - wherein the first rotational member is fully formed from a polymeric material containing magnetic particles, the polymeric material having been magnetized to provide a magnet producing the magnetic spatial field.