Low TSH: What It Means and What to Do Next
A low TSH level (below 0.4 mIU/L) means your thyroid is overactive — hyperthyroidism. Your pituitary reduces TSH because it detects excess thyroid hormone. Low TSH requires medical evaluation, as causes range from Graves' disease to thyroid medication overreplacement.
What Causes Low TSH?
Graves' Disease
The most common cause of hyperthyroidism. Autoimmune antibodies stimulate your thyroid to overproduce hormone.
Thyroid Nodules
Overactive nodules (toxic adenoma) can produce excess thyroid hormone independently of TSH control.
Thyroiditis
Inflammation of the thyroid can cause stored hormone to leak into the blood, temporarily suppressing TSH.
Excess Thyroid Medication
Taking too much levothyroxine or other thyroid medication is a common cause of low TSH.
Pituitary Dysfunction
Rarely, pituitary problems can reduce TSH production (central hypothyroidism — low TSH with low Free T4).
Associated Symptoms
What to Do Next
1. Retest to confirm
A single abnormal result should be confirmed with a repeat test. Temporary factors like stress, illness, or medications can affect results.
2. Related tests to consider
3. When to see a doctor
If your TSH is significantly abnormal, if you have severe symptoms, or if repeated results confirm the abnormality, consult a healthcare professional for appropriate evaluation and treatment.
Related Conditions
Frequently Asked Questions
Related Articles
Which thyroid tests you actually need to monitor Hashimoto's and track antibody levels.
How to get TSH, Free T4, and Free T3 tested affordably without insurance coverage.
Why Free T3 matters for thyroid health and when to add it to your panel.
This page is for informational purposes only and does not constitute medical advice. Consult a healthcare provider for interpretation of your results.
Content reviewed for accuracy by the JustLabs editorial team.