TSH
The pituitary signal to the thyroid - first-line thyroid test, but optimization requires free T4 + T3 context.
How TSH ranges relate
The standard lab range vs the optimization-focused target. Illustrative trajectory shows what a 12-week improvement pattern looks like — not real user data.
What TSH Measures
TSH (thyrotropin) is secreted by the pituitary to stimulate thyroid hormone production. Because the hypothalamic-pituitary-thyroid axis uses negative feedback, TSH rises when thyroid output is low and drops when it's high - making TSH a very sensitive marker of thyroid function.
Reference ranges on most lab reports are wide (0.4–4.5) and reflect population distribution, not optimal function. Functional-medicine and longevity clinicians typically target <2.0. Values in the 3–4.5 range are "normal" on paper but often coincide with subclinical hypothyroid symptoms.
TSH alone is insufficient for full thyroid assessment. Always pull free T4, free T3, and reverse T3 alongside it for the full picture.
What Affects This Biomarker
TSH is influenced by: thyroid gland function, pituitary health, iodine status, selenium and zinc, chronic inflammation, acute illness (non-thyroidal illness syndrome), recent contrast-dye exposure, and pharmacologic agents - levothyroxine suppresses TSH; lithium, amiodarone, and estrogen can raise it.
In the Context of Peptide Protocols
Track TSH annually for general health and quarterly if any thyroid dysfunction is suspected. On GH protocols (tesamorelin, HGH), thyroid status can shift - GH increases peripheral T4→T3 conversion, which can lower TSH slightly and warrant a full panel. Sub-2.0 TSH is fine if free T4 and free T3 are both in range.
Peptides That Commonly Move TSH
Related Reading
Conditions That Track TSH
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Start tracking →Informational only - not medical advice. Reference ranges vary by lab and individual context. Work with a licensed provider to interpret your specific results.