The injection brings his senses to a jittery, useless sort of energy, all awake at once with nowhere to go. And he can see and feel magical energies as though he'd put the Sight on himself, but everything is so nervous, so agitated, he can't quite focus.
While the drug certainly took effect, it seems Miach's mind is a bit more formidable than his captor would like. Oh well, just means it will take longer to bend him to her will.