lol, the root of the problem is something about driving around is causing him to be nervous. You shouldn't need to drug the dog.
If you have a significant other, get them to drive, and spend time with the dog in the back, making it an enjoyable experience. Also, if you drive more to dog parks and fun places, the dog will start to think the car is awesome again. Car = fun!
With cookie, for the first few car rides he got sick so when I was around I had the wife drive while I played with him in the back of the SUV. Its not exactly safe to not be wearing a seat belt, but it shows him that if we are not scared, he shouldn't be either.