I began levothyroxine therapy for hypothyroidism and am now experiencing hair loss; what is causing this and how should I evaluate and adjust my treatment?

Hair Loss with Levothyroxine: Evaluation and Management

Primary Cause and Immediate Action

Hair loss after starting levothyroxine is most commonly a temporary side effect of the medication itself, occurring rarely during the first few months of therapy, but you must also rule out inadequate thyroid replacement or overtreatment as potential causes. 1

Diagnostic Evaluation

Check Thyroid Function Status

• Measure TSH and free T4 levels immediately to determine if you are adequately replaced, under-replaced, or over-replaced 2
• Multiple tests over a 3-6 month interval should be done to confirm thyroid status, as TSH levels can be highly variable 2
• Under-treatment (persistent hypothyroidism) can cause ongoing hair loss, while over-treatment (iatrogenic hyperthyroidism) can also trigger hair shedding 3

Assess for Nutritional Deficiencies

• Check serum zinc levels, as zinc deficiency is required for thyroid hormone synthesis and absorption 4
• Hypothyroidism impairs zinc absorption, creating a vicious cycle where hair loss attributed to hypothyroidism may not improve with levothyroxine alone unless zinc is supplemented 4

Understanding the Hair Loss Pattern

Medication-Related Hair Loss

• The FDA label explicitly states that "partial hair loss may occur rarely during the first few months of levothyroxine sodium tablets therapy, but this is usually temporary" 1
• Drug-induced hair loss typically presents as diffuse, non-scarring telogen effluvium beginning 1-3 months after medication initiation 5
• Resolution occurs within 3-6 months as the body adjusts, with hair regrowth at approximately 1 cm/month 6, 5

Disease-Related Hair Loss

• Untreated or inadequately treated hypothyroidism itself is a well-recognized cause of diffuse hair loss 4, 3
• Thyroid hormones control hair follicle growth, differentiation, and metabolism 3

Treatment Algorithm

If TSH is Elevated (Under-Replaced)

1. Increase levothyroxine dose to achieve adequate thyroid hormone replacement 2
2. Add zinc supplementation (specific dose not provided in evidence, but supplementation is necessary) 4
3. Reassess thyroid function in 6-8 weeks 2

If TSH is Suppressed (Over-Replaced)

1. Reduce levothyroxine dose to avoid iatrogenic hyperthyroidism 2
2. Hyperthyroidism can cause widespread hair shedding 3
3. Recheck TSH in 6-8 weeks 2

If TSH is Normal (Adequately Replaced)

1. Reassure the patient that this is likely temporary medication-related hair loss that will resolve 1
2. Add zinc supplementation regardless, as hypothyroidism impairs zinc absorption even when adequately treated 4
3. Continue current levothyroxine dose without interruption 1
4. Monitor for improvement over 3-6 months, expecting hair regrowth at 1 cm/month 6, 5

Critical Management Points

Do Not Discontinue Levothyroxine

• Levothyroxine is life-maintaining replacement therapy that must be taken for life 1
• Stopping therapy will worsen hypothyroidism and paradoxically worsen hair loss 4, 3
• Case reports demonstrate that proper levothyroxine therapy leads to "substantial improvement in hair growth" when hypothyroidism is adequately treated 7

Set Realistic Expectations

• Hair growth occurs at approximately 1 cm/month, so patience is required when evaluating treatment response 6
• Improvement typically takes 3-6 months 5
• The hair loss is non-scarring and reversible 5

Common Pitfalls to Avoid

• Do not assume all hair loss is from the medication - inadequate thyroid replacement is a more common cause of persistent hair loss 4, 3
• Do not overlook zinc deficiency - this is an often-missed contributor that prevents hair regrowth despite adequate thyroid replacement 4
• Do not make treatment decisions based on a single TSH value - thyroid function should be confirmed with multiple tests over 3-6 months due to high variability 2
• Do not stop levothyroxine - this will worsen the underlying hypothyroidism and exacerbate hair loss 1, 7