well, to add a little personal insight here.
i have a cat, she is 11 years old this summer, we got her as a kitten from the human society when she was only 7 weeks old. 2 days after bringing her home (well, it started at the humane society) she got super sick, she almost died, she never became a cuddly kitty, basically won't let anyone touch her (as a child, she would corner me and i would have to call me mom to help me get away from her without being bitten or scratched), we suspect that a lot of it stems from being so sick for so long and being ripped of the attachments that cats tend to get as kittens to people (she hated the meds, so she hated the people who gave them to her. . .ie-us)
she started to have major allergies last year, and she needed to go to the vet, problem was that nobody wanted to see her (and nobody here wanted to take her). we finally found a vet that would see her, and well, he suggested at the time to try a hormone shot. it was for our well being,as wellas her's as she was so aggressive that she would freak in the vets office andbecame overly stressed out at the vets, in the car, while being givin meds ect.
we got her the shot, and well, it really works. . .we got 1 shot, about a year ago this fall. she got so cuddly for the first 3 months after the shot, that we couldn't stand it, and vowed that she would never get one again. after years and years of fearing this cat being anywere near our face (for fear of getting attacked) all she wanted to do was cuddle into your neck.
in the end it really helped her out, it has worn off considerably, and i have a feeling that she is only nice now because she got use to being nice while the shot was in effect. but we can get her to the vet now without to many problems, and i can pick her up if i need to, meds aren't a problem. in the end, i am very glade we did it, the benifits at the time out ruled the weight of the problems that might come with the shot.
i would only suggest getting the hormone shot for an animal if they can benifit it medically like it did with my kitty bagerrah. . .if she hadn't had medical problems, and if her aggressivness hadn't caused her such stress, we would never had done it.
tranqs were an option for us also, but as we had so many issues getting any kind of meds into her, we would have been poppin her tranqs so much she would have been a little kitty zombie. . . nothing seemed to calm her down, but the shot.