Your trainer sounds like a moron who has no idea how to train a horse why on earth would you ride a green horse drugged, that's just dangerous... The vet says he can't be taken out of his stall unless he's drugged... wth........... how is he hurt?
if the trainer is still drugging himand riding him he must not be injured that bad, if he is injured so bad that the vet says he can't come out of his stall unless he's drugged, then he should NOT be ridden
until he heals
Btw routinely drugging your horse can have serious health problems