why would he NEED to?
I've watched the first two episodes, and I can't believe no one on the show is asking this question. He is a handsome AND successful man, plenty of women would go to bed with him willingly, in fact probably younger and prettier women than she. And why would he have needed to drug this woman specifically - it's not like *she* was unwilling. If not on the first date, then surely on the second or the third.
I just don't see how this makes sense.