My 15yr old feline has hyperthyroidism, cannot tollerate ...

There is no effective natural approach to hyperthyroidism, according to a leading holistic veterinarian (Dr. Susan Wynn). It is a VERY treatable disease these days, with the use of I-131 therapy (radiotherapy). You do not have to just "keep him comfortable". The iodine treatment is very successful, and can return cats to normal within a month after treatment. If the oral medication is not tolerated, this is the best option for giving your cat a long life. If you do not treat it, there are several side effects that can be life threatening, including heart disease and liver disease.

Cats that are hyperthyroid will eat and eat and eat, and they will NOT gain weight unless the thyroid problem is addressed. If you want him to gain some weight and feel better then you need to treat the disease.

I hope you consider finding a vet who will do the iodine therapy. Here is some info on this disease/treatment:
http://www.marvistavet.com/html/thyroid.html

I unfortuinately can not afford 800$$, the pills made him so sick he seemed worse, constipated & vomiting, even when we lowered the dose.
What will happen to him?? will he someday just go to sleep? or should I consider putting him to sleep:-(

I'm sorry, I didn't know this was a financial issue :(

There are many cats who unfortunately cannot tolerate the oral medication. The side effects are sometimes very serious. So, I understand that this cannot be used for your cat.

I consulted an herbal medicine book written by Dr's Wynn and Mardsen (holistic vets). Here are some of their suggestions for alternative therapies. You will need to find a holistic vet to work with, hopefully you can find one in your area.

Carnitine: found in humans to prevent symptoms of hyperthyroidism. Starting dose for cats 250-500 mg divided daily.

Herbs bugleweed and melissa: a combination of these herbs has been found to normalize the T4 levels and can extend life without conventional therapies.

There are also other alternative therapies that were listed, but you need a vet experienced in alternative/holistic medicine to guide you through the treatment. I doubt this would be inexpensive in the long run, but it certainly might be something to look into.

I can't say for sure what will happen to your cat without treatment. I think the worse side effect it has on the body is affecting the heart. It is possible he could die of a sudden heart attack, or experience heart failure, but I can't predict that for you. If I were to guess, I would say the heart might give out first.

I don't think he needs to be put to sleep unless you think he is suffering. If he is eating well and acting normal, I would continue with what you are doing for now. Perhaps trying to find a holistic vet near you also for alternative therapies.

You might also check this out: www.carecredit.com
They offer financing for veterinary treatments, and might be an option for getting the radiotherapy paid for.