Thyroid medication and its effect on hair
Both underactive and overactive thyroid disease cause hair loss, and so, confusingly, can starting treatment for them.
Both underactive and overactive thyroid disease cause hair loss, and so, confusingly, can starting treatment for them. Hair generally recovers once thyroid function is stable, which is why stability matters more than the direction of the initial change.
Why does thyroid disease affect hair?
Thyroid hormones regulate the body's metabolic rate, and hair follicles are highly metabolically demanding, so both too little and too much thyroid hormone disrupt the growth cycle and push follicles into a resting phase, causing diffuse scalp thinning rather than a pattern, sometimes with eyebrow changes in hypothyroidism.
Why does starting or adjusting thyroid medication cause hair shedding?
The approved prescribing information for levothyroxine notes that partial hair loss may occur rarely during the first few months of treatment, and that it is usually temporary. It says nothing about dose adjustments, and no published study has tested whether changing the dose triggers shedding. Untreated thyroid disease is itself a well-documented cause of diffuse shedding, so stopping the medication is rarely the answer.
What should you expect for hair recovery after thyroid treatment changes?
Once thyroid function stabilises, hair recovery generally takes months rather than weeks. Telogen effluvium generally follows its trigger by two to five months, so hair is a slow indicator and blood tests normalise long before hair does. Persistent loss despite stable thyroid function points to another cause running alongside it.
- Recovery generally follows once thyroid function is stable, over months rather than weeks
- Telogen effluvium generally follows its trigger by two to five months
- Hair is a slow indicator; blood tests normalise long before hair does
- Persistent loss despite stable thyroid function suggests another cause running alongside
Why should thyroid function be checked before a hair transplant?
Undiagnosed or unstable thyroid disease is a treatable cause of hair loss, so operating on it addresses the symptom rather than the problem, and it's one of the tests worth having before attributing diffuse loss to pattern baldness, especially in women. High-dose Biotin interferes with thyroid assays, so disclose supplements before testing.
Thyroid disease is one of the non-hereditary causes listed under causes of hair loss.
Sources
- Hussein RS, Atia T, Bin Dayel S. Impact of Thyroid Dysfunction on Hair Disorders. Cureus, 2023;15(8):e43266. pubmed.ncbi.nlm.nih.gov/37692605
- Asghar F, Shamim N, Farooque U, Sheikh H, Aqeel R. Telogen Effluvium: A Review of the Literature. Cureus, 2020;12(5):e8320. pubmed.ncbi.nlm.nih.gov/32607303
- Kumar A, Karthikeyan K. Madarosis: a marker of many maladies. International Journal of Trichology, 2012;4(1):3-18. pubmed.ncbi.nlm.nih.gov/22628984
- Grover C, Khurana A. Telogen effluvium. Indian Journal of Dermatology, Venereology and Leprology, 2013;79(5):591-603. pubmed.ncbi.nlm.nih.gov/23974577
- Li D, Radulescu A, Shrestha RT, et al. Association of Biotin Ingestion With Performance of Hormone and Nonhormone Assays in Healthy Adults. JAMA, 2017;318(12):1150-1160. pubmed.ncbi.nlm.nih.gov/28973622
This article summarises published research. It is general educational information, not medical advice, and it is not a recommendation to start, stop or change any medication. Prescription drugs carry contraindications and interactions; discuss them with a doctor who knows your medical history.
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