Don't be surprised if the vet responds with either "I don't know if that will help" (as few medical studies have actually been done on it) or "I'm not allowed to advise you on that" (in some states, vets cannot recommend CBD).
I bought some for my big dog but it was too sporadic for us to get good results as her anxiety was noticeable all the time (you need to dose a certain amount of time before you're leaving or whatever else may be causing anxiety) so she's now on Prozac, but the CBD does work really well for my middle dog who is scared of fireworks or other loud noise - it doesn't make him lethargic, but takes off the edge.