When used at the correct dose, Essential T2 should not have an impact on thyroid lab tests. This is based on studies that show that using doses of up to 300mcg per day does not significantly impact TSH, free T3, and free T4 levels. Whenever you are trying to improve your thyroid function, though, whether that be through natural therapies or with the use of thyroid medications, it's always a good idea to keep an eye on your thyroid lab tests. If you notice a change in how you are feeling then rechecking your thyroid lab tests (with a complete thyroid lab panel) would be a good idea after 6-8 weeks of continuous use. With physician supervision, if you see changes in your thyroid function then you can make appropriate changes to your thyroid medication at that time.