The first thing I'd do is go back to the vet. Hyperthyroid can be a difficult condition, and I'd want to know exactly what's going on - especially as the meds are still relatively new to him. I hope everything goes ok [article="32998"][/article][article="33011"][/article]
If you have a facebook join the hyperthyroid cats group. Those people are super smart and can help with issues related to hyper t meds. Apparently, a lot of vet's over-medicate.
In the interim, make sure you get kitty back to the vet because not eating is a sign there's a problem.
My 15 year old cat had some trouble with the thyroid medication and did the same thing. I had to take him off the medication and syringe feed him because he became absolutely uninterested in the food. When it hit the 3rd day, the vet said to take him off the medication and then make sure he got at least 2.5 oz of the AD food twice a day. Luckily he started eating on his own after about 4 days of syringe feeding, but it was definitely the medication. It was complicated because he also had a sniffle and was on an antibiotic (high white blood count). So I personally wasn't sure which medication was causing the problem. But the vet should be able to figure out if it is the medication or something else.
Tuesday he stopped eating. The vet told me to continue his meds. Friday I come home from work and found he didn't touch his water. I had a bad feeling ...... I tried to give him a couple eye dropper fullls of water. After 10pm Mr. Pook passed away.
I had a feeling it could be kidneys as well.
I'm heart broken. He was in our life for a little over 17 years. I will miss him dearly.
Such sad news. We'll lock the thread now out of respect for your loss. We invite you to post a tribute to your sweet boy in our Crossing the Bridge forum.