Originally Posted by DaDOKin DC

As a physician, I will echo ermdjdsj's comment -- first TALK TO YOUR DOCTOR. You might be taking another med or have a medical condition that makes even the 'safe' OTC drugs dangerous.

For OTC meds, your choices boil down to
Benedryl/diphenydramine (get the generic, the extra $$ is not worth it) -- however, the paradoxical effect of revving you up, that cejkwj mentioned is true.
Chor-Trimeton/chlorpheniramine may also work
Dramamine/dimenhydrinate, usually used for motion sickness, also makes people drowsy
Melantonin -- max dose of 3 mg may work

For US prescription meds, the best choices are
Ambien, Sonata -- be aware these should be used for short-term use only, as there is a possible for dependency if taken for an extended time (to be safe, not beyond 7-10 days)

Whatever you choose, try it out before you travel, to be sure you get the intended effect and it neither lasts too long (hangover effect) or too short. Although many people swear by Ambien and Sonata, there are some people for whom they do not work (like myself, I get too zonked by Ambien).