Opie

I have a 13 year old Tabby - he was recently diagnosis with Hypothyroid condition.   We are still waiting on test results to come back on his urine so we have not started a medical treatment yet.  They have prescribed Mirtazapine to increase his appetite - first pill was given last evening - so I thought we would wake up today to him starving  - no such luck.  Today has been a heart ache in trying to get him to eat - he has been drinking but as for eating - in total it hasnt even been a 1/4 cup and I have tried everything.  He acts hungry and comes running to you but smells the food and walks away.  And what little he did eat today - he vomited it all up.  My next try is to get him baby food and syringe feed.   I have been hearing to cut this with Pedialyte but am unsure of how much to feed at each time.  His normal diet was a 1/2 can / 2x per day of Fancy Feast - classic.  Any suggestions.

Is he hypothyroid or hyperthyroid?

They has advised it is Hypothyroid

Hypothyroidism in cats is actually very rare.  When it does occur it is usually caused by too high of a dose of the medication to treat hyperthyroidism.  Does your vet have plans to give hormone replacement?  

It sounds like your cat is nauseated.  The behavior of acting excited smelling the food and walking away happens a lot with nausea.  It could be the appetite stimulant rather than the thyroid condition.  I wouldn't give him anymore than see if he is able to keep food down tomorrow. 

It is actually difficult to find anything on hypothyroidism in cats.  I did find this https://www.vetinfo.com/feline-hypothyroidism-symptoms.html    When I would try to google it there are one or two articles on it and the rest are about hyperthyroidism.