Which kind of drug slows down the functioning of the nervous system?

Answer 1

Are you talking about legal drugs? I'm going to assume so.

Butalbital is one prescription drug I know of that slows down the central nervous system. I'm currently taking Fioricet for my tension headaches, which contains butalbital, acetaminophen, and caffeine. I've found it to be pretty helpful.

Here's a little information on butalbital:
http://en.wikipedia.org/wiki/Butalbital

Answer 2

Alcohol and marijuana are the most commonly used.