From wikipedia...
A study in the UK found that only 2 percent of a pool of 1,014 rape victims had their drinks spiked with sedatives.[6][7] Another UK study of 75 patients, most of them women, who thought their drinks had been tampered with in pubs or clubs found that none had been given a surreptitious drug. They had simply become intoxicated.[8] Similarly, a 2009 Australian study concluded that, of 97 patients admitted to hospital claiming to have had their drinks spiked, none had in fact been drugged.[9]
I honestly believe it is largely an urban legend and that most people just drink themselves ****faced then get taken advantage of