For the thyroid system to be working at peak levels, the body must be able to convert most of the hormone the thyroid gland secretes, called T4, into a five-times more active substance, called T3. The body then signals itself not to convert the T4 into T3. Instead, it makes an inactive chemical called reverse T3. This problem is called Wilson's syndrome, or low-T3 syndrome. Here's where your thermometer comes in handy.
Body temperature is the most reliable way to determine thyroid activity.
This will also correspond to more symptoms and greater severity. That could be anything from starting a new diet, or becoming pregnant to going through a major illness or emotional crisis. The T3 corrects the thyroid slowdown. Because the gland itself functions normally, you often will be able to end the medication and remain healthy. Thyroid system malfunctions are very common, but not nearly so readily diagnosed.