What Are Thyroid Stimulating Hormones?

Q: What Are Thyroid Stimulating Hormones?

TSH (thyroid-stimulating hormone) explained: how the pituitary regulates the thyroid, normal ranges, and what abnormal TSH levels indicate about thyroid function.

TSH (thyroid-stimulating hormone) is produced by the pituitary gland and tells the thyroid how much hormone to produce.

How It Works

Hypothalamus releases TRH → pituitary releases TSH → thyroid releases T3/T4
Negative feedback: when T3/T4 are adequate, TSH is suppressed

Normal Range

0.4–4.0 mIU/L for adults

What Abnormal TSH Means

High TSH = thyroid underperforming (hypothyroidism)
Low TSH = thyroid overperforming (hyperthyroidism)

Source: American Thyroid Association, NLM MedlinePlus.

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