There is only one way to treat hyperthyroidism without medication, radiation, or surgery: Speak with your veterinarian about Hills y/d diet. The real trick with this is that your cat can eat NOTHING else. Not a single bite of human food that falls in your kitchen. Not a single bite of another cat food. You can’t run out on the weekend and just run to the store for another food for a couple of days.
Some cats can maintain by severely restricting iodine intake. There is no other diet or supplement on the market that can do this. If it works for your cat, great! Then you don’t need more aggressive treatment, at least for now.
Don’t waste your time, your money, and your cat’s health on supplements to reduce thyroid levels. This is a scientific problem, with a scientific solution that works.