The fact is, there is no 100% way of preventing such crimes, aside from completely separating the sexes.
I suppose that a woman COULD refuse any drink or food if she needs to leave a table for any reason. After all, if her current paramour WANTED to, he could have slipped in a drug.
But, such women tend to be very unpopular with young men because they become paranoid to the point of being unable to trust. Most young men want the object of their affections to be able to trust them.
Therefore, greater onus is on the man for NOT drugging the food than for the woman to assume (as she must, to ensure her safety 100%) that any food or drink that she hasn’t watched during the duration of their time together is potentially drugged.
It sounds like we’re pretty much on the same page here.