I think it was in England about 5 years ago that they did a big study about gals who came in saying they had been given a date-rape drug and then raped. They did the study for a couple of years; everyone who showed up within 8 hours of saying this happened, they tested to see if there was any trace of the drug in their system. In something like 95%, no drug other than alcohol (and lots of it) was found in their system. Blackouts and/or passing out from good old booze is generally what happens.