I didn't overhear this at the vets but when i worked in a pet shop a woman came in and asked for sedatives. When i asked why she need them she told me that she works all day and would like to give the dog sedatives so it sleeps until she gets home.
I told her that she needed to think seriously about rehoming the dog.

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Grandma to Jinja Dog, Mum to Tilly the Cavalier, Tattycat, Moomy, Choo, Sonic, Niven Mc Twisp and Lawna the rabbits and 1 guinea,17 budgies, 4 Cockatiels, 8 Goldfish.

Not that long back someone in here asked about sedating a cat for flying (in a plane) …. I replied that as far as I was a aware this was dangerous and not ever done (something to do with the effect pressurized cabins have on the metabolic rate of cats. The sedation could kill them). I advised them to check with a vet and a pet relocation company and they did and were told the exact same thing I told them. No sedatives for cats in planes. The person then PMed me to say they had sedatives left over from some other thing at the vets and did I think it would be ok to just give one (after a vet had told them NO, ABSOLUTELY NOT).