What scruples bother Macbeth's conscience when he thinks about killing Duncan?

Macbeth's main scruple is his loyalty and duty to Duncan as king, as well as his gratitude for being named Thane of Cawdor and his close relationship with Duncan as his kinsman and guest. He is also troubled by the prospect of the consequences of his actions, both in terms of his own fate and the chaos it may unleash on Scotland.