Generally speaking, I believe that's it's true, the MD's order the drugs, HOWEVER, in our hospital, if you are ACLS certified, (as I am) I can run a code without an MD, or rather until the MD gets there.
I have run many codes, someone has to call the shots and keep things orderly, since most people shy away from that, I would usually step up to the plate. I would never deviate from ACLS protocol though.
I'm always very happy to give up running the code when the MD arrives.