TSH (Thyroid Stimulating Hormone)
TSH is released by the pituitary to stimulate thyroid hormone production and provides negative feedback regulation of the thyroid axis. Elevated TSH typically indicates primary hypothyroidism as the pituitary tries harder to stimulate an underperforming thyroid, while low TSH suggests hyperthyroidism or central pituitary disease. TSH is the preferred first-line test for thyroid dysfunction.
Units: mIU/L; some labs report µIU/mL (same number in both units). Check the units on your report before comparing to any range here.
Optimal range: who says what
Institutions, researchers and practitioners draw the line in different places. Each position is listed with who holds it and, where a document states it, a link. How we verify ranges.
- Institution or study0.4-2.5 mIU/LNACB laboratory medicine practice guidelines: over 95% of rigorously screened healthy adults fall in this bandThe standard 0.4-4.5 reference range includes people with early thyroid dysfunction
- Named practitioner0.5-2.5 mIU/L (optimal vs 0.45-4.12 standard)Rupa Health · A Functional Medicine Approach to Thyroid Hormone Labs
- Named practitioner0.5-2.5 mIU/L, 60-80th percentile associated with lowest mortalityHealthline · Optimal Thyroid Levels for Males and Females
- Named practitioner1-2 μIU/mLLife Extension · Lab Testing Protocol (Suggested Optimal Ranges)Disclosure: Life Extension sells lab panels that appear in our blood-test comparisons.
- Named practitioner0.5-2.0 mIU/LTracey O'Shea (Kresser Institute) · Beyond TSH: How Functional Medicine Reads Thyroid Labs Differently
- Named practitioner1.8-3.0 mIU/LChris Kresser · Five Thyroid Patterns That Won't Show Up on Standard Lab Tests
- Lab reference interval0.45-4.5 mIU/L, adults (Labcorp)What a lab report flags against. A lab interval is not an optimal target.
Practitioner targets are individual positions, often tighter than guideline ranges. Each was checked against its article before publishing.
19 of 21 itemized panels
Thyroid Function
What is TSH (Thyroid Stimulating Hormone)?
TSH (Thyroid Stimulating Hormone) is a hormone produced by your pituitary gland that regulates your thyroid gland's production of thyroid hormones (T4 and T3). Think of TSH as the "thermostat" for your thyroid: when thyroid hormone levels drop, your pituitary releases more TSH to tell the thyroid to produce more hormone. When thyroid hormone levels are sufficient, TSH drops.
High TSH means your thyroid is underactive (hypothyroidism), while low TSH means your thyroid is overactive (hyperthyroidism). It's an inverse relationship—TSH goes up when thyroid function goes down, like a thermostat cranking up the heat when the house is too cold.
TSH is the single most important initial screening test for thyroid function. However, TSH alone doesn't tell the full story—you also need Free T4 and Free T3 to understand what's actually happening at the tissue level. Some people have normal TSH but low Free T3 due to conversion problems, and they'll have hypothyroid symptoms despite "normal" labs.
Why TSH Alone Isn't Enough
- Central hypothyroidism: Pituitary gland failure causes low TSH + low thyroid hormones (rare but serious)
- T4→T3 conversion problems: Normal TSH/T4 but low Free T3 due to stress, selenium deficiency, chronic illness
- Subclinical hypothyroidism: Elevated TSH with normal Free T4—controversial whether to treat
- Hashimoto's (autoimmune) thyroiditis: TSH may be normal early on but TPO antibodies are elevated
Interpretation bands (curated, PMID-backed)
Holder: OptimizeBiomarkers editorial synthesis of: The optimal healthy ranges of thyroid function defined by the risk of cardiovascular disease and mortality: systematic review and individual participant data meta-analysis (Xu et al., 2023); Prognostic impact of thyroid stimulating hormone levels in patients with cardiomyopathy (Azemi et al., 2013); Subclinical hypothyroidism and the risk of coronary heart disease and mortality (Rodondi et al., 2010). No single paper sets these cutoffs; for attributed targets see who says what.
Optimal (Longevity)0.5-2.5 mIU/L▼
- Best metabolic function, energy, and symptom control
- Many functional medicine doctors target this range
Low-Normal (Borderline Low)2.5-4.0 mIU/L▼
- Within standard range but may have subtle hypothyroid symptoms
- Consider retesting in 3-6 months or checking antibodies
Subclinical Hypothyroidism4.0-10.0 mIU/L▼
- Thyroid struggling but Free T4 still normal
- Controversial treatment threshold
- Consider treatment if symptomatic or trying to conceive
Overt Hypothyroidism>10.0 mIU/L▼
- Clear thyroid failure; requires treatment
- Free T4 will be low
- Start levothyroxine and retest in 6-8 weeks
- The optimal healthy ranges of thyroid function defined by the risk of cardiovascular disease and mortality: systematic review and individual participant data meta-analysis.
- Prognostic impact of thyroid stimulating hormone levels in patients with cardiomyopathy.
- Subclinical hypothyroidism and the risk of coronary heart disease and mortality.
What raises or lowers TSH
Causes of high TSH
- Hashimoto's thyroiditis: Autoimmune attack on thyroid gland. Most common cause of hypothyroidism in iodine-sufficient countries (5-10% prevalence, 7:1 female:male ratio). Check TPO antibodies.
- Iodine deficiency: Rare in developed countries (iodized salt) but most common cause worldwide. Thyroid can't make T4/T3 without iodine.
- Thyroid surgery or radioactive iodine treatment: Surgical removal or ablation of thyroid gland for cancer, nodules, or hyperthyroidism.
- Medications: Lithium (bipolar disorder), amiodarone (heart arrhythmias), high-dose iodine, interferon.
- Pituitary or hypothalamus disorders: Rare. Tumor, trauma, or Sheehan's syndrome (postpartum pituitary necrosis) causes low TSH despite hypothyroidism ("central hypothyroidism").
- Congenital hypothyroidism: Born with absent or malfunctioning thyroid gland. Screened at birth in developed countries.
Causes of low TSH
- Graves' disease: Autoimmune condition where antibodies stimulate thyroid to overproduce hormone. Most common cause of hyperthyroidism. Associated with bulging eyes (Graves' ophthalmopathy).
- Toxic nodular goiter: Thyroid nodules autonomously produce excess thyroid hormone independent of TSH control.
- Thyroiditis (inflammation): Subacute, postpartum, or silent thyroiditis causes stored thyroid hormone to leak out, temporarily suppressing TSH. Usually self-limited.
- Excessive thyroid hormone medication: Over-replacement with levothyroxine or taking thyroid hormone without medical supervision (weight loss abuse).
- Pituitary adenoma (rare): TSH-secreting tumor causes high thyroid hormones + high TSH (opposite of usual pattern).
Symptoms when TSH is high or low
When high
- Persistent fatigue, low energy despite adequate sleep
- Weight gain or inability to lose weight
- Cold intolerance (always feeling cold, cold hands/feet)
- Brain fog, poor concentration, memory problems
- Depression, low mood, anxiety
- Dry skin, brittle nails, hair loss or thinning (especially outer third of eyebrows)
- Constipation, sluggish digestion
- Slow heart rate (bradycardia)
- Muscle weakness, joint pain
- Heavy or irregular menstrual periods
- Infertility or difficulty conceiving
- Puffy face, swelling around eyes
- High cholesterol (especially LDL)
High TSH = hypothyroidism (underactive thyroid). These are the symptoms when TSH is elevated.
When low
- Rapid or irregular heartbeat (palpitations, atrial fibrillation)
- Anxiety, nervousness, irritability
- Tremors (especially hands)
- Unexplained weight loss despite normal or increased appetite
- Heat intolerance, excessive sweating
- Insomnia, difficulty sleeping
- Frequent bowel movements or diarrhea
- Muscle weakness (especially in upper arms and thighs)
- Eye problems (bulging eyes in Graves' disease)
- Light or absent menstrual periods
- Increased energy initially, followed by fatigue and burnout
Low TSH = hyperthyroidism (overactive thyroid). These are the symptoms when TSH is suppressed.
How to move TSH
Effect sizes (how much something moves the marker) appear only where the paper cited under the item states them. Talk to your clinician before starting or changing any medication or supplement.
Treat Underlying Hypothyroidism
- Levothyroxine (Synthroid, generic T4): Standard treatment. In overt hypothyroidism the usual starting dose is about 1.6 mcg/kg/day, and the dose is then titrated to the TSH target your clinician sets, commonly within the lab reference interval: Chiovato et al. (2019) give 0.4-4.0 mIU/L as the usual titration target. Take on empty stomach, 30-60 minutes before food.
- T4/T3 combination therapy: Some patients feel better adding T3 (liothyronine/Cytomel) to levothyroxine, especially if Free T3 remains low. Typical ratio: 4:1 or 5:1 (T4:T3).
- Natural desiccated thyroid (NDT): Armour Thyroid, NP Thyroid. Contains both T4 and T3 from pig thyroid. Some patients prefer it but evidence is mixed.
Source: Hypothyroidism in Context: Where We've Been and Where We're Going.
Optimize Thyroid-Supporting Nutrients
- Iodine (150-300 mcg/day): Essential building block of thyroid hormones (T4 has 4 iodine atoms, T3 has 3). Seaweed, iodized salt, seafood. Caution: Excess iodine (>400 mcg) can worsen Hashimoto's in susceptible individuals.
- Selenium (200 mcg/day): Critical for thyroid hormone synthesis and T4→T3 conversion. Also reduces TPO antibodies in Hashimoto's. Brazil nuts (2-3/day), seafood, organ meats.
- Zinc (15-30 mg/day): Required for thyroid hormone production and conversion. Oysters, red meat, pumpkin seeds.
- Iron: Iron deficiency impairs thyroid peroxidase enzyme, worsening hypothyroidism. Check ferritin; supplement if low.
- Vitamin D: Deficiency linked to higher risk of Hashimoto's and hypothyroidism.
Address Hashimoto's Thyroiditis (if TPO antibodies elevated)
- Hashimoto's is the most common cause of hypothyroidism (90% of cases in iodine-sufficient countries). It's an autoimmune attack on the thyroid gland.
- Selenium supplementation: 200 mcg/day lowered TPO antibodies in several small trials; the effect on thyroid function is less clear.
- Gluten-free diet: Some Hashimoto's patients improve on gluten-free diet due to molecular mimicry between gliadin and thyroid tissue.
- Stress management: Chronic stress exacerbates autoimmune conditions. Meditation, sleep, adaptogenic herbs may help.
Lifestyle Factors
- Avoid goitrogens in excess: Raw cruciferous vegetables (broccoli, kale, cauliflower) contain goitrogens that can interfere with iodine uptake. Cooking inactivates them. Not a problem unless iodine-deficient or eating massive amounts raw.
- Avoid soy in large amounts: Soy isoflavones may interfere with thyroid hormone synthesis if iodine intake is marginal.
- Timing of levothyroxine: Take 30-60 minutes before breakfast on empty stomach. Avoid calcium, iron supplements, coffee within 4 hours (impair absorption).
Treat Hyperthyroidism (if TSH <0.4)
- Low TSH indicates overactive thyroid. Check Free T4/T3 (will be elevated). Causes include Graves' disease, toxic nodular goiter, thyroiditis.
- Treatment options: Antithyroid medications (methimazole, PTU), radioactive iodine ablation, or surgery. Work with endocrinologist.
When to retest
- If starting or adjusting thyroid medication: Retest TSH, Free T4, Free T3 after 6-8 weeks of any dose change.
- Once stable on treatment: Retest every 6-12 months to ensure dose remains appropriate.
- If subclinical hypothyroidism (TSH 4-10): Retest in 3-6 months to see if it progresses. Check TPO antibodies to assess autoimmune risk.
- If optimizing for longevity/symptoms: Retest 3 months after implementing iodine, selenium, or lifestyle changes to assess impact.
- Routine screening: Every 5 years starting at age 35, or sooner if family history, autoimmune disease, or symptoms.
Scientific Evidence
TSH as the First Screening Test
The AACE/ATA guideline names serum TSH as the single best screening test for primary thyroid dysfunction in most outpatient settings. Standard treatment for hypothyroidism is levothyroxine, and the decision to treat subclinical hypothyroidism with TSH below 10 mIU/L should be made patient by patient.
The Case for a Narrower TSH Range
Wartofsky and Dickey argue that older TSH reference ranges were inflated by people with undiagnosed thyroid disease. They cite National Academy of Clinical Biochemistry guidance that more than 95% of people without thyroid disease have TSH below 2.5 mU/L, and propose that most people above that have underlying Hashimoto's thyroiditis. This is one side of an open debate, not a consensus reference range.
Source: The evidence for a narrower thyrotropin reference range is compelling.
Hypothyroidism Prevalence and Treatment Target
Hypothyroidism affects up to 5% of the general population, with an estimated further 5% undiagnosed. Where iodine intake is sufficient, Hashimoto's disease is the most common cause. Levothyroxine is usually titrated to a TSH of 0.4-4.0 mIU/L, and nearly one-third of treated patients still report symptoms.
Source: Hypothyroidism in Context: Where We've Been and Where We're Going.
Subclinical Hypothyroidism: Treat or Monitor?
A 2019 BMJ guideline panel, drawing on 21 trials with 2,192 participants, recommends against thyroid hormone for most adults with subclinical hypothyroidism (raised TSH, normal free T4). Treatment gave no meaningful benefit for quality of life, fatigue, depressive symptoms, or body mass index. The recommendation does not cover women trying to conceive or people with TSH above 20 mIU/L, and may not apply to young adults or people with severe symptoms.
Source: Thyroid hormones treatment for subclinical hypothyroidism: a clinical practice guideline.
Which Providers Test TSH (Thyroid Stimulating Hormone)?
Cheapest: Empirical Health at $190/year. Most comprehensive: Function Health, 160+ biomarkers for $365/year.
19 panels that include it, cheapest first
| Provider | Annual Cost | Total Biomarkers | $/Biomarker |
|---|---|---|---|
| $190 | 100+ | $1.90 | |
| $297 | 100+ | $2.97 | |
 Labcorp OnDemand | $338 | 50+ | $6.76 |
 Superpower | $349 | 100+ | $3.49 |
| $349 | 75+ | $4.65 | |
 WHOOP Advanced Labs | $349 | 65 | $5.37 |
 Function Health | $365 | 160+ | $2.28 |
| $365 | 100+ | $3.65 | |
| $375 | 108 | $3.47 | |
| $449 | 83 | $5.41 | |
| $495 | 80+ | $6.19 | |
| $499 | 100+ | $4.99 | |
| $700 | 138 | $5.07 | |
| $829 | 54 | $15.35 | |
| $895 | 100+ | $8.95 | |
| $996 | 59 | $16.88 | |
| $1188 | 70+ | $16.97 | |
| $1198 | 40+ | $29.95 | |
| $1950 | 130+ | $15.00 |
$/Biomarker is annual cost divided by the panel's advertised biomarker count, not the price of this one test. We track 23 blood test providers (32 plans); 21 of those plans are itemized marker by marker. Compare all of them.
2 itemized panels do not include TSH (Thyroid Stimulating Hormone)
11 providers not itemized in our matrix
We have not itemized these marker by marker (some sell tests one at a time), so this page cannot say whether they offer TSH (Thyroid Stimulating Hormone). Check with them directly.
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Experts discussing TSH (Thyroid Stimulating Hormone)
Podcast episodes where clinicians and researchers cover this marker in depth. Curated by hand; an episode is listed only when the marker is a substantial topic, not a passing mention.
- Check These Biomarkers on Your Next Blood Test
- A Deep Dive Into How To Interpret The Results Of Your Blood Testing
- Testosterone Replacement Therapy, Hormone Testing 101, and More
- Which Lab Tests are Essential?
- Understanding the Gut-Thyroid Axis, Hypothyroidism, and Hashimoto's
- Your Lab Tests Are Normal But You Feel Sick: What Your Doctor Is MissingDisclosure: Hyman co-founded Function Health, which appears in our blood-test comparisons.
Frequently Asked Questions
What is the optimal range for TSH (Thyroid Stimulating Hormone)?
Published position: 0.4-2.5 mIU/L (NACB laboratory medicine practice guidelines: over 95% of rigorously screened healthy adults fall in this band). Named practitioners target: 0.5-2.5 mIU/L (optimal vs 0.45-4.12 standard) (Rupa Health); 0.5-2.5 mIU/L, 60-80th percentile associated with lowest mortality (Healthline); 1-2 μIU/mL (Life Extension); 0.5-2.0 mIU/L (Tracey O'Shea (Kresser Institute)); 1.8-3.0 mIU/L (Chris Kresser). Lab reference interval: 0.45-4.5 mIU/L, adults (Labcorp). That is what a lab report flags against, not an optimal target.
Which blood test providers include TSH (Thyroid Stimulating Hormone)?
19 of the 21 blood testing panels we itemize marker by marker include TSH (Thyroid Stimulating Hormone) in their panels. This biomarker is widely available across major providers.
Related: YouBoost rates lifestyle and supplement interventions by evidence.
Medical Disclaimer
This information is for educational purposes only and is not medical advice. Always consult with a qualified healthcare provider about your specific health needs.
Last reviewed Sep 23, 2026 · First published Sep 30, 2025