We first tried meds but they had side effects like itching and making him
want to bite himself, then he was put on a med for the side effects and it
made him a zombie cat.   We then brought my Toby to Radiocat (do a search).
It cost $1,000 but he was cured of any thyroid condition and bought us 10
more years with Toby.

The medication is the simplest and least expensive way to go, and if
you are fortunate, it will fix all.  Side effects include nausea,
vomiting and diarrhea, which so far, my cat has had none.  Masked
effects include a suppression of the white blood cell count, so you
need to do lab work from time to time to know that the WBC count is not
so low that the cat is vulnerable to infection which could be lethal.
Also, if your cat is a bit older, or has severe hyperthyroid, then high
blood pressure could have damaged the kidneys, in which case you will
also need periodic blood work to assess the renal function (ideally
every six months or so, once kitty is stable on the meds).  The newest
meds, however, rarely cause this effect (the WBC effect), unlike the
original PTU (propothiouracil).  The current favourite is Tapazol
(methimazole) and so far, we are sailing on it.  By the way, both these
meds are used in humans too for the same thing.

The other option is radioactive iodine treatment, which the other
poster opted for, it sounds like.  A dose of Iodine-131 is given, which
is absorbed almost exclusively by the thyroid, hence no consequences
for other tissues, and the radioactivity sits there and works just like
radiotherapy for a cancer patient, killing off thyroid cells.  If you
are lucky and all calculates out well, the dose given will be just
enough to stop the hyperthyroidism, but the calculated risk of this
treatment is that if the amount of the dose is *not* just right, you
can inadvertently kill off the entire thyroid gland, and the cat then
ends up on medicine anyway, though it will only be thyroxine, or
thyroid hormone replacement.

Like the other poster, you should try the meds first and see if your
cat is a sensitive one who can't cope with the meds,  Radiation therapy
is an expensive but not unreasonable alternative in that case, but
don't be disappointed if you spend all that money and your cat ends up
on medicine anyway.

---tension