High tsh

Written to our editorial standards · reviewed against published research· Updated 2 Jun 2026
A medical finding, review with a doctor

A high TSH usually means the thyroid is underactive (hypothyroidism), which causes fatigue, weight gain, cold intolerance, and low mood. This is a medical diagnosis to discuss with a doctor.

TSH is the signal the brain sends to the thyroid, so it rises when the thyroid is sluggish and the body is trying to push it harder. The most common cause is autoimmune (Hashimoto's). Selenium supports thyroid enzymes and iodine is the raw material, but an underactive thyroid is treated by a doctor, often with thyroid hormone, not by supplements.

Common causes

  • Autoimmune thyroiditis (Hashimoto's)
  • Iodine deficiency or excess
  • Previous thyroid treatment
  • Certain medications
  • Recovery from illness (transient)

Associated symptoms

  • Fatigue
  • Weight gain
  • Feeling cold
  • Dry skin and hair
  • Constipation
  • Low mood

Nutrients that can help

Selenium
See the guide →
Vitamin D3 + K2
See the guide →
What to do

This is a result to take to your doctor. Selenium (and adequate, not excessive, iodine) supports thyroid function, but confirmed hypothyroidism is managed medically with monitoring.

When to see a doctor

Always review a high TSH with a doctor, who will repeat it, check thyroid antibodies and free T4, and decide on treatment. Do not mega-dose iodine, which can worsen thyroid problems.

Full marker
TSH: ranges, what it measures & both directions
Read the TSH guide →

Common questions

What does high tsh (underactive thyroid) mean?
A high TSH usually means the thyroid is underactive (hypothyroidism), which causes fatigue, weight gain, cold intolerance, and low mood. This is a medical diagnosis to discuss with a doctor. TSH is the signal the brain sends to the thyroid, so it rises when the thyroid is sluggish and the body is trying to push it harder. The most common cause is autoimmune (Hashimoto's). Selenium supports thyroid enzymes and iodine is the raw material, but an underactive thyroid is treated by a doctor, often with thyroid hormone, not by supplements.
What causes high tsh?
Autoimmune thyroiditis (Hashimoto's); Iodine deficiency or excess; Previous thyroid treatment; Certain medications; Recovery from illness (transient).
How do I lower my tsh?
This is a result to take to your doctor. Selenium (and adequate, not excessive, iodine) supports thyroid function, but confirmed hypothyroidism is managed medically with monitoring.
When should I see a doctor?
Always review a high TSH with a doctor, who will repeat it, check thyroid antibodies and free T4, and decide on treatment. Do not mega-dose iodine, which can worsen thyroid problems.

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Educational use only, not medical advice or diagnosis. Reference ranges vary by lab, age, sex, and medication, and a single result is read in context. Always review your results with a qualified clinician.