Detailed definition
Thyroid-stimulating hormone (TSH), also called thyrotropin, is a glycoprotein hormone secreted by the anterior pituitary in response to hypothalamic thyrotropin-releasing hormone (TRH). TSH stimulates the thyroid follicular cells to take up iodide and produce thyroxine (T4) and triiodothyronine (T3). T4 and T3 then feed back negatively on both the pituitary and hypothalamus. TSH is the most sensitive single test for thyroid dysfunction because the pituitary amplifies small changes in circulating thyroid hormone — a 50% drop in T4 produces roughly a 100-fold rise in TSH. Reference ranges vary by laboratory but typically run 0.4–4.5 mIU/L. Subclinical hypothyroidism (elevated TSH with normal T4) is common in women over 50, with prevalence around 5–10%. Symptoms of hypothyroidism — fatigue, weight gain, cold intolerance, dry skin, hair thinning, depression, cognitive slowing — overlap heavily with perimenopausal symptoms.
Why it matters in menopause
Hypothyroidism is the most common imitator of perimenopause. A woman who comes in with brain fog, fatigue, and weight gain may have low estrogen, low thyroid, or both. Treating only the menopause when thyroid is also off underwhelms the patient. The minimum baseline workup before starting menopause treatment should include TSH; ClearedRx and most evidence-based menopause practices include this in their intake.