Turns out, poor Bruiser falls into the minority who have side effects from the meds. It's pretty much scrubbed his white blood cell count, and his thyroid has gone back up again, which means the meds stopped working at some point. He's asymptomatic otherwise, and his weight was even slightly higher than it was in February which is good. Except for this, he's incredibly healthy and very energetic. So energetic, in fact, that the vet was a little shocked to find out he's 12 years old. He doesn't act like a 12-year-old cat, that's for sure.
We have three options, which is really only two because surgery just isn't a real option because too much can go wrong. There's a diet means of helping his thyroid, but that's a) expensive, and b) hard to do in a multi-cat household like ours. Plus, if he doesn't like it because, hello, he's a cat, it's a waste of time.
So we're going for the iodine treatment, which is actually a cure. It requires hospitalization, and it's $1500 upfront, but it's almost always effective and he won't have to worry about it afterward. I'm going to call tomorrow and see when we can get it scheduled. I imagine with the upcoming holiday, we'll have to wait until the week after.
I'm just glad he's so healthy otherwise. He might annoy me sometimes--I swear, I have never owned such a vocal or social cat--but he's my baby.