As the disease progresses, you would need to adjust
thyroid replacement medication, periodically,
in order to keep up with the decline
in thyroid function.
Once properly diagnosed, and started on medication, it can take a while to get things adjusted to where YOU need them, not just "in range". Some people can accomplish this in 6 months, for others, that's way too optimistic, but it depends a lot on your doctor and the tests s/he runs.