TSH (thyroid-stimulating hormone) is a pituitary signal that tells your thyroid how much hormone (T3 and T4) to make. When thyroid hormones are too high, TSH levels drop as part of your body’s feedback system. A low TSH can therefore mean your thyroid is producing too much hormone — a condition called hyperthyroidism — or it may simply reflect recent medication or health changes.
Tip: TSH can drop temporarily after illness or thyroid hormone dose adjustments. Always check
free T4 and
T3 before assuming a thyroid disorder.
Common causes of low TSH
- Graves’ disease (autoimmune hyperthyroidism)
- Toxic multinodular goiter or thyroid nodules
- Excessive thyroid medication (levothyroxine or liothyronine)
- Early pregnancy
- Recovery phase of thyroiditis
- Pituitary or hypothalamic disorders (rare)
Symptoms that may accompany low TSH
- Rapid heartbeat or palpitations
- Weight loss despite normal eating
- Anxiety or tremors
- Heat intolerance or sweating
- Sleep difficulties
How to interpret TSH with other thyroid markers
- TSH ↓ + T4/T3 ↑ → hyperthyroidism (active overproduction)
- TSH ↓ + T4/T3 normal → subclinical hyperthyroidism (monitoring often recommended)
- TSH ↓ + T4/T3 ↓ → possible pituitary dysfunction (secondary hypothyroidism)
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