When on the meds Toby developed a habit of biting himself, pulling his hair
out.  He would be walking across a room and all of a sudden sit down and
start viciously licking and biting himself like he was being attacked by
invisible bugs.  The vet then put him on another med for the side effects,
though I don't remember what, but it was probable something like valium or
an anti-anxiety med.  He then was a zombie and just slept all the time.
Then we opted for the radiation treatment and he was wonderful for 8 more
years of his life.

Tapazole is also known for causing vomiting, and diarrhea.  It isn't
because of the taste, as Phil mentioned, but a direct side effect of
the medication.  It apparently happens often enough that the vets
forewarn of it, which is important because one needs to sort out
vomiting as a side effect of the med, vs. vomiting as a symptom
of hyperthyroidism.  That's partly why following levels is so
important.

Luthien is 14 years old, and just got diagnosed this
summer.  Her initial T4 levels were 19.6, apparently the highest
her vet has ever seen.  Her little heart was banging away at
240 bpm, poor thing.  She started on 5mg daily
(half-tab twice a day), and that got her T4 down to 4.63 which is
just above normal for this lab.  And her heart rate is down to 120 bpm,
at home when she is calm.  But her Free T4 was still greater than
100 (normal is 10-50) so vet has asked us to increase the dose
by fifty percent.  I was a bit skeptical, since her heart rate was
back to normal, but I followed directions.  We'll see her levels
again, but fortunately she is having no side effects on meds
at 7.5mg per day.  For now, the criteria for me is to follow
her heart rate, which is a quite sensitive indicator for thyroid
levels.  If you can get kitty to sit still long enough to measure
it.

Medicine time is quite a show in this house.  I felt bad popping
pills down Luthien twice a day, knowing it would be for life,
even though she is a great pill taker.  But it was ruining the
fun of her treat time, knowing she had to take the meds, so
now I crunch it up in her food, because she always finishes
the whole plate, so I know she gets all the meds, and the
food hides the taste quite well, and the kitten gets a plate
of treats at the same time so as not to get jealous, and they
never horn in on each other's food and now everybody's happy.

--tension