There is also another med called Acepromazine. I think that is the correct spelling. It calms them down...makes them sleepy and tends to help with any upset tummies. But the best thing to do is to talk to you vet about the best thing to do. The trouble with Valium is that it doesn't ALWAYS work like it is suppose to. Some cats do not relax on it at all. They lose their inhibitions but become more wired. It is also a appetite stimulant. Not always a good thing on a long car trip. You want to feed your cat smaller amounts of food but make sure he does still eat and get plenty of water. Good Luck!

Denyce