What does TSH measure and what is an optimal range?
TSH (thyroid stimulating hormone) is the pituitary signal that drives thyroid hormone production. It is the most sensitive screening marker of thyroid function. Conventional ranges run roughly 0.4–4.5 mIU/L; many optimization frameworks target the lower-mid range when reading TSH with free T3, free T4, and TPO antibodies.
Full answer
TSH is produced by the pituitary in response to circulating thyroid hormone and is the most sensitive single screening marker for thyroid dysfunction. A high TSH suggests the pituitary is pushing harder because thyroid output is falling (hypothyroidism); a suppressed TSH suggests too much thyroid hormone (hyperthyroidism or over-replacement). Conventional reference ranges span roughly 0.4–4.5 mIU/L, but provider-reviewed wellness rarely reads TSH alone. Free T3, free T4, reverse T3, and TPO antibodies build the full picture — including whether an autoimmune driver (Hashimoto's) is present. Many optimization frameworks target a TSH in the lower-mid range when symptoms persist at the upper end of 'normal', individualized to the patient.
Educational. Not a substitute for individualized provider review.
- TSH — Primary source · oMeds
- Thyroid intelligence — Reference · oMeds Learn
- Reviewed by Dr. Laura Purdy, MD, MBA · Clinical Director, oMeds · Last reviewed 2026-05-29