Our ferrets get an overdose of Phenobarbital in the stomach.  There
doesn't seem to be any pain other than the initial stick and they just
go to sleep and then their heart stops.  Doing heart sticks it seems to
me to be very painful and I wouldn't have that done for anything.
 
I'm not a vet but have had many ferrets euthanized when there was no hope
and they quit eating and taking their medicine
 
Win and our living ferts
[Posted in FML issue 4877]