 Your thyroid has a finite output, and it's just not going to be enough to power your metabolism. So an effort was made to put you on thyroid medication. So let's explain that TSH. TSH is usually high when you have a low thyroid. I know that sounds paradoxical, but it's what's called a reflex test. It's high when your thyroid is low, and it's low when you suffer from hyperthyroidism or Graves' disease or when you're getting too much thyroid medication.