What specific sedative did your vet have in mind? We really need that information to talk about effectiveness and side effects intelligently. You can view part of an avian medicine book published in 2015 at https://books.google.com/books?id=LK...ots%22&f=false
It talks about psychoactive drugs starting at the bottom of page 219. It starts talking about specific drugs at the bottom of page 221, breaking them into five categories where the first one and possibly the second one seem like they would be the most relevant. There are a number of different types within each category, and they probably have different levels of effectiveness and side effects. If we have the name of a specific drug we can research it to see how good or bad it looks.
Edited to add: they start talking about feather destructive behavior on page 226 and get into treatment on page 231. In terms of drugs, they suggest antihistamines (which seems to be a common treatment for plucking problems), and on page 233 they mention other drugs that can be used.
I'm not sure exactly why antihistamines would be helpful. Birds can have allergies just like humans can, and antihistamines would be useful if the plucking was caused by an undiagnosed allergy. I don't know whether there are other reasons that antihistamines might help.