What is TSH?
Thyroid-stimulating hormone (TSH) is released by the pituitary gland to tell the thyroid how much thyroid hormone to produce. It works on a feedback loop: when thyroid hormone is low, TSH rises to stimulate more; when thyroid hormone is high, TSH falls. TSH is the most sensitive first-line screen for thyroid dysfunction.
Why it matters
TSH abnormalities are common and highly treatable. High TSH usually means an underactive thyroid (hypothyroidism); low TSH usually means an overactive thyroid (hyperthyroidism). Thyroid status affects metabolism, energy, mood, weight, and heart rate.
What it measures
Serum TSH concentration, typically the first test ordered, then followed by free T4 and free T3 if abnormal.
Reference & optimal ranges
Reference ranges vary by lab, assay, age, and sex. The ranges below reflect commonly published adult intervals and are for education only always interpret results with the range printed on your own lab report and a clinician.
High TSH indicates the pituitary is pushing an underperforming thyroid hypothyroidism.
Common symptoms
- Fatigue
- Weight gain
- Cold intolerance
- Dry skin, hair loss
- Constipation
- Depressed mood
Potential causes
- Hashimoto's thyroiditis (autoimmune)
- Iodine deficiency
- Thyroid surgery or radiation
- Certain medications
Low TSH indicates the thyroid is overproducing hormone hyperthyroidism.
Common symptoms
- Weight loss
- Rapid heartbeat, palpitations
- Anxiety, tremor
- Heat intolerance, sweating
- Insomnia
Potential causes
- Graves' disease (autoimmune)
- Toxic nodules
- Excess thyroid hormone medication
- Thyroiditis (early phase)
How to improve your TSH
Lifestyle
Take thyroid medication consistently
If prescribed levothyroxine, take it on an empty stomach at the same time daily and retest as advised.
Nutrition
Adequate iodine and selenium
Both support thyroid hormone production; avoid extremes.
Exercise
Regular activity
Supports metabolism and mood while thyroid status is optimized.
Sleep
Prioritize sleep
Thyroid dysfunction disrupts sleep; treating it usually helps.
Frequently asked questions
Scientific references
- Thyroid-Stimulating Hormone (TSH) Test Testing.com
- TSH (Thyroid-Stimulating Hormone) Test MedlinePlus, U.S. National Library of Medicine
Educational information, not medical advice. This page is for general education and does not replace diagnosis or treatment by a licensed clinician. Do not start, stop, or change any medication, supplement, or treatment based on this content. Reference and optimal ranges vary between laboratories interpret your results with the range on your own report and a qualified professional.