TSH (Thyroid Stimulating Hormone)

What is TSH?

Thyroid Stimulating Hormone (TSH) is produced by the pituitary gland in your brain. It tells your thyroid gland how much thyroid hormone to produce. TSH is the most sensitive marker for detecting thyroid dysfunction.

Think of TSH as a thermostat: when thyroid hormone levels are low, TSH rises to stimulate more production. When thyroid hormones are high, TSH drops.

Normal Ranges

Status	TSH Level (mIU/L)
Hyperthyroid	Below 0.4
Normal	0.4 – 4.0
Subclinical Hypothyroid	4.0 – 10.0
Hypothyroid	Above 10.0

Note: "Normal" ranges vary by lab and are debated. Many practitioners consider optimal TSH to be 1.0-2.0 mIU/L.

Why It Matters

Metabolism

Your thyroid controls your metabolic rate. Dysfunction can lead to unexplained weight gain or loss, fatigue, and temperature sensitivity.

Energy & Mood

Thyroid hormones affect brain function. Low thyroid is associated with depression, brain fog, and fatigue. High thyroid can cause anxiety and irritability.

Heart Health

Both hypo- and hyperthyroidism affect heart rate and can increase cardiovascular risk if left untreated.

Reproductive Health

Thyroid dysfunction can cause menstrual irregularities, fertility issues, and pregnancy complications.

Symptoms of Thyroid Dysfunction

Hypothyroidism (High TSH)

Fatigue and sluggishness
Weight gain
Cold intolerance
Dry skin and hair
Constipation
Depression

Hyperthyroidism (Low TSH)

Anxiety and irritability
Weight loss
Heat intolerance
Rapid heartbeat
Tremors
Insomnia

Beyond TSH: The Full Thyroid Panel

TSH alone doesn't tell the whole story. Consider testing:

Free T4 — The main hormone produced by the thyroid
Free T3 — The active form of thyroid hormone
Thyroid antibodies — To detect autoimmune thyroid disease (Hashimoto's, Graves')

How Often to Test

If healthy with no symptoms: Every 5 years after age 35
If you have symptoms: Get tested immediately
If on thyroid medication: Every 6-12 weeks when adjusting dose, then annually
During pregnancy: Each trimester