Mate all this stuff can be given orally it takes a little longer to work but it is a lot safer. Don't be sucked in by the jab merchants there is always a chance of something going wrong with injections. Of course some times they can't be avoided. but I try to avoid myself and my animals being stuck by sharp objects
Plus greys are pretty smart he might get a bit leary next time he sees you coming at him with a needle! Fitness and nutrition is the go in the first instance. Good luck I hope you get plenty of wins with him!