What Is TSH?
TSH stands for Thyroid Stimulating Hormone. It's produced by the pituitary gland in your brain and tells your thyroid gland to produce thyroid hormones (T3 and T4). Think of TSH as the thermostat for your thyroid.
The Counterintuitive Part
Here's what confuses most people: high TSH usually means your thyroid is underactive (hypothyroidism), not overactive. When your thyroid isn't producing enough hormones, your pituitary sends more and more TSH to try to stimulate it — like turning up the thermostat when the room is cold.
Normal TSH Ranges
| Range | Interpretation |
|---|---|
| 0.4 – 4.0 mIU/L | Normal |
| 4.0 – 10.0 mIU/L | Mildly elevated (subclinical hypothyroidism) |
| Above 10.0 mIU/L | Significantly elevated (likely hypothyroidism) |
| Below 0.4 mIU/L | Low (possible hyperthyroidism) |
Symptoms of Hypothyroidism
If your TSH is elevated, you might experience:
- Fatigue and low energy
- Unexplained weight gain
- Feeling cold all the time
- Dry skin and hair loss
- Brain fog and poor concentration
- Constipation
- Low mood or depression
- Muscle aches and stiffness
What Causes High TSH?
- Hashimoto's thyroiditis — An autoimmune condition and the most common cause in the UK
- Iodine deficiency — Uncommon in developed countries but still possible
- Medications — Lithium, amiodarone, and some others can affect thyroid function
- Pituitary disorders — Rarely, the pituitary itself can be the issue
- Recovery from illness — TSH can temporarily rise after being unwell
What to Do If Your TSH Is High
1. Don't panic — A mildly elevated TSH often just needs monitoring 2. Retest in 6–8 weeks — TSH can fluctuate, so a single reading isn't definitive 3. Request a full thyroid panel — Ask for free T4 (fT4) and thyroid antibodies if not already tested 4. Track it over time — Use CheckMyBloods to spot trends in your thyroid markers 5. See your GP — If TSH is above 10.0 or you have symptoms, discuss treatment options
Treatment
The standard treatment for hypothyroidism is levothyroxine, a synthetic thyroid hormone taken daily. Once on the right dose, most people feel significantly better within weeks.
