really, anything in the classification of central nervous system depressants, except for alcohol. I tend to lean toward the ones that cause respiratory depression as well, even though i've almost not woke back up many of times and sometimes i'll suddenly freak out and wake up because i quit breathing. I highly do not recommend it though. Bad idea for a sleep solution, but sleep isn't my reason for it, thats just an added benefit... otherwise i'd never get any damned sleep.