Can levothyroxine really make my hair fall out, or is something else going on?

By Sina Hartung, MMSC-BMI, Harvard Medical SchoolReviewed by Eureka Health Medical Group
Published: June 16, 2025Updated: June 16, 2025

Summary

Levothyroxine itself rarely causes permanent hair loss, but sudden shedding can occur when the dose is too high, too low, or changed too quickly. Transient thinning is most common in the first 3–6 months after starting or adjusting therapy and usually improves once thyroid hormone levels stabilize. If hair loss continues beyond six months, ask your clinician to review your thyroid labs, iron status, and other potential causes.

Does levothyroxine itself trigger hair shedding?

Most people blame the pill, yet the real culprit is usually an imbalanced thyroid level rather than the medication molecule. Both hypothyroidism and hyperthyroidism can push hair follicles into a resting phase, leading to diffuse shedding called telogen effluvium.

  • Hair loss peaks during dose changesClinical studies show up to 30 % of patients report increased shedding within 12 weeks of starting levothyroxine or having their dose altered.
  • Steady levels protect folliclesOnce TSH stabilizes between 0.5–2.5 mIU/L, shedding typically stops within one to two hair cycles (6–12 months).
  • True drug allergy is extremely rareLess than 0.1 % of users have reported eruption-type rashes or alopecia linked to filler sensitivity, not to the hormone itself.
  • Quote from Sina Hartung, MMSC-BMI"In most cases, hair loss signals that the thyroid dose hasn’t caught up with the body’s needs yet—not that levothyroxine is toxic to the follicle."
  • Excess hormone dosing can precipitate reversible diffuse alopeciaA case report showed that an infant given 14 µg/kg/day of levothyroxine developed sudden scalp hair loss that resolved after the dose was corrected, underscoring that supratherapeutic levels—not the drug itself—disrupt the follicle cycle. (PMC)
  • Nearly 1 in 7 Synthroid reviewers report hair loss as a side effectAnalysis of user reviews found 14.1 % mentioning hair loss, reflecting how patients often notice shedding while dosage is still being optimized. (Drugs.com)

References

When is thyroid-related hair loss a red flag that needs urgent attention?

Occasional extra strands in the brush are common, but some patterns demand prompt evaluation to avoid permanent thinning.

  • Rapid loss of eyebrow outer thirdsThis classic sign may mean severe hypothyroidism and warrants same-week testing.
  • Clumps coming out within days of a dose increaseA TSH that has swung to suppressed levels (<0.1 mIU/L) can trigger acute telogen effluvium.
  • Visible scalp redness or scaly patchesCould indicate alopecia areata or fungal infection co-existing with thyroid disease.
  • Quote from the team at Eureka Health"Any hair loss accompanied by heart palpitations, weight changes over 5 lb in two weeks, or new tremor should trigger an urgent thyroid panel."
  • Diffuse shedding plus fatigue or cold intolerance is a warning signExcessive hair coming out all over the scalp together with weight gain, dry skin, low energy, or feeling unusually cold for several weeks is flagged by The Independent Pharmacy as a reason to seek immediate thyroid testing. (TIP)

References

How can I tell if the dose, not the drug, is the problem?

Matching symptoms with lab results is the fastest way to identify dose-related hair loss. Keep a timeline of dose changes and shedding episodes.

  • Look for a 6–8 week delayHair follicles react a few weeks after hormone shifts; timing helps pinpoint the cause.
  • TSH outside 0.5–2.5 mIU/L rangeBoth high and low levels correlate with increased shedding in cohort analyses.
  • Free T4 rising faster than TSH normalizesThis lab pattern often appears when titration happens too quickly in seniors.
  • Quote from Sina Hartung, MMSC-BMI"I ask patients to bring a calendar of dose changes and hair-wash photos—pattern recognition is powerful."
  • Patient-reported data show 14 % experience hair loss that often lessens after dose adjustmentIn Drugs.com user reviews, 14.1 % of Synthroid reporters listed hair loss, and many note that shedding eased once their physician fine-tuned the dosage rather than discontinuing therapy. (Drugs.com)
  • Over-replacement at 14 µg/kg/day caused diffuse alopecia that reversed when the dose was correctedA published case of a 10-month-old on an excessive levothyroxine regimen developed significant scalp hair loss, which fully regrew within months after reducing the hormone dose—illustrating dose-driven, not drug-driven, shedding. (PMC)

References

Practical steps at home to protect and regrow your hair

While your provider fine-tunes the dose, several evidence-based measures can reduce shedding and support regrowth.

  • Ensure 18–20 mg of iron dailyFerritin below 40 ng/mL doubles the risk of telogen effluvium in thyroid patients—consider iron-rich foods or supplements if recommended.
  • Add 2,500 mcg of biotin only if deficientRoutine high-dose biotin can skew thyroid labs; test levels first.
  • Use mild, sulfate-free shampoosHarsh detergents increase breakage and can mimic ongoing loss.
  • Limit heat styling to under 150 °CHigh heat weakens the hair shaft already stressed by hormonal shifts.
  • Quote from the team at Eureka Health"Small tweaks like lowering flat-iron temperature often give patients visible improvement within a month."
  • Revisit your levothyroxine dose if shedding persistsConsensus reports that dosage mis-adjustment can provoke anagen effluvium and notes that “monitoring and adjusting levothyroxine dosage” helps prevent and reverse medication-related loss. (Consensus)
  • Rule out scalp conditions such as seborrheic dermatitisEureka Health highlights that persistent thinning accompanied by a greasy or flaky scalp may signal treatable issues like fungal infection or seborrheic dermatitis, and that addressing them can halt further fallout. (Eureka)

References

Which labs and medication adjustments matter most for thyroid-related alopecia?

Targeted testing guides precise dose correction and uncovers other reversible causes.

  • Full thyroid panel every 6–8 weeks after changesTSH, Free T4, and sometimes Free T3 provide the clearest picture during titration.
  • Check ferritin, vitamin D, and zincLow levels are present in 40 % of women with chronic telogen effluvium.
  • Consider switching formulationsPatients sensitive to certain dyes or fillers may improve when moved to a dye-free tablet or gel cap.
  • Avoid abrupt dose jumps over 25 mcgGradual steps prevent transient hyperthyroidism that shocks follicles.
  • Quote from Sina Hartung, MMSC-BMI"A single ferritin result under 30 ng/mL can undo months of perfect TSH control in terms of hair outcomes."
  • Early levothyroxine titration can trigger temporary sheddingMild telogen effluvium is a known adverse effect and usually resolves within the first few months as hormone levels stabilize. (Drugs)
  • Hair regrowth can take several months after thyroid balance returnsThe British Thyroid Foundation notes that regrowth is typical once thyroid status is corrected, but the process may be delayed for several months and may be erroneously attributed to the medication itself. (BTF)

References

How Eureka’s AI doctor supports fine-tuning your thyroid treatment

Eureka’s virtual doctor uses guideline-based algorithms to interpret your labs, symptoms, and hair-loss patterns, suggesting questions to bring to your clinician.

  • Personalized dose-adjustment suggestionsEureka flags when your trend predicts a TSH out of range before labs are drawn.
  • Photo-based shedding trackerUpload scalp photos; the AI measures density changes as small as 5 %.
  • Integrated nutrient reminderThe app nudges you to take iron or vitamin D at times that won’t block levothyroxine absorption.
  • Quote from the team at Eureka Health"People using the dosing-trend feature reach target TSH 30 % faster than those using paper logs."

Using Eureka to track hair regrowth and medication effects over time

Once your dose stabilizes, ongoing monitoring keeps shedding from sneaking back.

  • Symptom scores plotted against lab resultsSee in one graph how fatigue, palpitations, and hair density shift with every TSH point.
  • Secure messaging with cliniciansAsk whether a 12.5 mcg adjustment is safer than 25 mcg; a doctor reviews within 24 hours.
  • Automated refill and lab remindersMissing a single pill can raise TSH by 10 %—the app prevents gaps.
  • High user satisfactionUsers managing thyroid-related hair loss rate Eureka 4.7 / 5 for helping them feel heard.
  • Quote from Sina Hartung, MMSC-BMI"Consistent tracking turns a frustrating guessing game into a data-driven plan patients can trust."

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Frequently Asked Questions

How long does hair loss last after starting levothyroxine?

Most people notice shedding for 6–12 weeks, with regrowth beginning once TSH stabilizes, usually by month six.

Should I stop levothyroxine if my hair keeps falling out?

Stopping suddenly can worsen thyroid imbalance and make hair loss worse; talk to your clinician about dose adjustment first.

Can I switch to a natural desiccated thyroid to stop hair loss?

Some patients feel better on other formulations, but benefits for hair are not proven; switching requires new labs and careful titration.

Will biotin interfere with my thyroid tests?

High-dose biotin (>5 mg) can falsely lower TSH and raise T4; stop it 2–3 days before blood draws unless your doctor advises otherwise.

Does coloring my hair affect thyroid-related shedding?

No, but avoid harsh bleach during active telogen effluvium; gentle semi-permanent dyes are safer while follicles recover.

Is hair loss worse if I take levothyroxine with coffee?

Coffee can cut absorption by up to 30 %, leading to under-treatment and increased shedding; take the pill with water on an empty stomach.

Can men on levothyroxine get the same hair loss?

Yes, although male-pattern balding may coexist; checking thyroid labs and ferritin applies to all genders.

How soon after a dose change should I repeat labs?

Guidelines advise 6–8 weeks to allow TSH equilibrium, unless severe symptoms develop sooner.

This content is for informational purposes only and is not intended as medical advice. Always consult with a qualified healthcare provider for diagnosis, treatment, and personalized medical recommendations.

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