TSH (Thyroid-Stimulating Hormone)
TSH is a hormone produced by the pituitary gland that tells the thyroid gland how much thyroid hormone to produce. It is an exquisitely sensitive marker of thyroid function: when thyroid hormone levels fall, the pituitary releases more TSH to stimulate the thyroid; when thyroid hormone is high, TSH is suppressed. It is the first-line test for any suspected thyroid disorder.
Normal Range
0.4–4.0 mIU/L (standard adult range; optimal often cited as 0.5–2.5 mIU/L)
Reference ranges may vary slightly between laboratories. Always interpret your result in context with your doctor.
Why is TSH measured?
Thyroid disorders — particularly hypothyroidism (underactive thyroid) and hyperthyroidism (overactive thyroid) — are among the most common endocrine conditions, affecting 200 million people worldwide. TSH is tested for fatigue, weight changes, mood disturbances, menstrual irregularities, hair loss, and heart palpitations.
High TSH means…
A high TSH indicates your thyroid is underproducing hormones and the pituitary is working harder to stimulate it. This is hypothyroidism. Common in women over 60, it causes fatigue, weight gain, cold intolerance, constipation, and depression.
Low TSH means…
A low TSH means thyroid hormone levels are high — hyperthyroidism. The thyroid is overactive and the pituitary reduces TSH output. Causes include Graves' disease, toxic nodular goitre, or excess thyroid medication. Symptoms include weight loss, rapid heartbeat, anxiety, and heat intolerance.
Symptoms associated with abnormal TSH
When TSH is high:
- Fatigue and weakness
- Weight gain despite normal eating
- Cold intolerance
- Constipation
- Dry skin and hair loss
- Low mood or depression
- Heavy or irregular periods
When TSH is low:
- Unexpected weight loss
- Rapid or irregular heartbeat (palpitations)
- Anxiety and irritability
- Heat intolerance and sweating
- Tremor in hands
- Difficulty sleeping
- Frequent bowel movements
How to improve your TSH
- Take levothyroxine (if prescribed) consistently — same time each morning, 30–60 minutes before food, for reliable absorption.
- Avoid taking thyroid medication with calcium, iron supplements, or antacids as these block absorption.
- Adequate iodine intake is essential for thyroid health: seafood, dairy, and iodised salt are good sources.
- Selenium (found in Brazil nuts, tuna, eggs) supports thyroid enzyme function — 1–2 Brazil nuts per day provides your daily selenium.
Frequently asked questions about TSH
What is a normal TSH level?
The standard laboratory reference range for TSH is 0.4–4.0 mIU/L, though many endocrinologists consider an optimal range of 0.5–2.5 mIU/L. TSH naturally varies with age — older adults typically have slightly higher TSH. Pregnant women have lower reference ranges, especially in the first trimester.
Can stress affect TSH levels?
Yes. Acute psychological stress activates the hypothalamic-pituitary-adrenal axis and can temporarily suppress TSH. Chronic stress and cortisol elevation can impair the conversion of T4 to active T3 thyroid hormone. This can cause thyroid symptoms without a true thyroid disorder.
Medical Sources
This page is for informational purposes only and does not constitute medical advice. Always consult a qualified healthcare provider about your individual results.