Hypothyroidism
An underactive thyroid
What it is
Hypothyroidism is insufficient thyroid hormone production. It is usually autoimmune (Hashimoto's thyroiditis), is common — particularly in women and with age — and produces fatigue, weight gain, cold intolerance, constipation, dry skin, and low mood. It is diagnosed by a raised TSH with a low free T4, and treated effectively with levothyroxine.
Why it matters
Overt hypothyroidism is one of endocrinology's clearest wins: cheap, safe, effective treatment that transforms how people feel. The difficulty lies at the margins. Subclinical hypothyroidism — a raised TSH with a normal free T4 — is frequently treated without benefit, while over-replacement causes atrial fibrillation and bone loss. And a genuine subset of properly treated patients remain symptomatic, a problem that is real, commonly dismissed, and not solved.
What BioSignal knows about treating this
What works for Hypothyroidism
BioSignal’s clinical summary, most important first.
- Levothyroxine, titrated to TSH — effective, cheap, usually lifelong
- Taken fasting, separated from coffee, calcium, and iron (absorption is genuinely sensitive)
- Careful dose review to avoid over-replacement (which causes atrial fibrillation and bone loss)
- In subclinical disease: often monitoring rather than treatment, particularly in older adults
- Investigating other causes when symptoms persist despite a normal TSH
Signal Records relevant to this condition
Interventions and contributing factors — some of these records describe a cause rather than a cure. The rating shown is BioSignal’s confidence in that Signal Record, not a claim about how well it treats this condition. Open any of them for the full evidence.
- LevothyroxineHigh confidence
Highly effective for overt hypothyroidism. Frequently over-prescribed for subclinical disease, where trials show no symptom benefit.
- AshwagandhaLimited evidence
The best-evidenced hormone supplement — a modest stress effect. Weak testosterone evidence, and a real liver-injury signal that the label won't mention.
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How this usually unfolds
- Recognize risk factors
- Get diagnosed
- Track key biomarkers
- Lifestyle first
- Evidence-based treatment
- Long-term monitoring
Who is at risk
- Female sex
- Older age
- Autoimmune disease (personal or family history)
- Previous thyroid surgery or radioiodine
- Certain medications (amiodarone, lithium)
- Iodine deficiency (globally the leading cause; uncommon where salt is iodised)
- Postpartum period
How it's diagnosed
Diagnosis rests on TSH and free T4 read together. A raised TSH with a LOW free T4 is overt hypothyroidism and warrants treatment. A raised TSH with a NORMAL free T4 is subclinical hypothyroidism, where the case for treatment is much weaker. TPO antibodies identify an autoimmune cause. Biotin supplements interfere with many thyroid assays and should be stopped before testing.
Key biomarkers
Lifestyle
Explore this condition across BioSignal
Related Foundations
Related Signal Records
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Frequently asked questions
My TSH is slightly high but my T4 is normal. Do I need levothyroxine?
Often not. That is subclinical hypothyroidism, and a randomised trial in older adults found levothyroxine gave no improvement in symptoms or tiredness compared with placebo. Treating it exposes you to the risks of over-replacement for a benefit that hasn't been shown. Exceptions exist — a markedly raised TSH, positive antibodies, or pregnancy — so it's a discussion, not a rule.
I take levothyroxine and my TSH is normal, but I still feel awful. Why?
This is real, it happens to a genuine subset of patients, and being told it's impossible is not good medicine. What we must also say honestly is that the popular fixes — adding T3, or switching to desiccated thyroid extract — have not been shown to work in trials. It's worth checking the other things that cause these symptoms: anaemia, low B12, sleep apnoea, and depression all overlap heavily with hypothyroidism.
Will more levothyroxine help my fatigue?
No — and this is where real harm occurs. Pushing your dose above what you need creates a state like an overactive thyroid, raising the risk of atrial fibrillation and thinning your bones. Over-treatment is common, and tiredness has many causes.
Evidence summary
Levothyroxine for overt hypothyroidism is highly effective and well established. In subclinical hypothyroidism, randomised evidence (notably the TRUST trial in older adults) found no symptom benefit, and routine treatment is not supported. T4/T3 combination therapy has not been shown superior in trials, and desiccated thyroid extract is not recommended.
References & sources
- ATA Guidelines for the Treatment of Hypothyroidism
- TRUST trial (levothyroxine in subclinical hypothyroidism in older adults)
Educational information — not medical advice
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