Can tirzepatide or levothyroxine (thyroid hormone replacement medication) cause hair thinning or loss, especially in patients with a history of thyroid issues?

Hair Loss and Levothyroxine vs. Tirzepatide

Levothyroxine can cause temporary hair loss during the first few months of therapy, but this is usually transient and resolves with continued treatment; conversely, untreated hypothyroidism itself is a major cause of hair loss that improves with proper levothyroxine replacement. 1 Tirzepatide is not documented to cause hair thinning or loss in the available evidence.

Levothyroxine and Hair Loss: The Paradox

Hair Loss as an Adverse Effect of Levothyroxine

The FDA label for levothyroxine explicitly lists hair loss as a dermatologic adverse reaction, particularly when therapeutic overdosage occurs 1. This hair loss is part of the hyperthyroid symptom complex that can develop with overtreatment 1.

• Partial hair loss may occur rarely during the first few months of levothyroxine therapy, but this is usually temporary 1
• The mechanism involves drug-induced telogen effluvium, where levothyroxine precipitates hair follicles into premature rest phase 2
• Hair loss typically becomes evident 2 to 4 months after starting treatment when telogen effluvium is the mechanism 2

The Critical Distinction: Hypothyroidism Causes More Hair Loss Than Treatment

Untreated hypothyroidism is itself a major cause of hair loss, listed among the cardinal symptoms including fatigue, muscle cramps, constipation, and cold intolerance 3. This creates a clinical paradox where both the disease and its treatment can cause hair loss.

• A 13-year-old girl with juvenile hypothyroidism presented with significant hair loss leading to balding involving frontal, temporal, and occipital areas of the scalp 4
• After 2 months of levothyroxine treatment, there was substantial improvement in hair growth as TSH normalized from >100 mIU/mL to 1.51 mIU/mL 4
• Extensive hair loss is a cardinal symptom of hypothyroidism and should improve within 3-4 months of adequate levothyroxine replacement 5

Clinical Management Algorithm

When Hair Loss Occurs in Patients on Levothyroxine

Step 1: Check TSH and Free T4 Levels

• If TSH is suppressed (<0.1 mIU/L), the patient is overtreated and experiencing iatrogenic hyperthyroidism causing hair loss 1
• Reduce levothyroxine dose by 25-50 mcg immediately to prevent continued hair loss and other complications 5
• If TSH is elevated (>4.5 mIU/L), the patient is undertreated and hair loss is from persistent hypothyroidism 3, 5
• Increase levothyroxine dose by 12.5-25 mcg to normalize thyroid function 5

Step 2: Timing Assessment

• If hair loss began within the first 2-4 months of starting levothyroxine and TSH is in normal range (0.5-4.5 mIU/L), this represents temporary drug-induced telogen effluvium 1, 2
• Reassure the patient that this is usually self-limited and will resolve with continued therapy 1
• If hair loss persists beyond 6 months despite normal TSH, consider other causes unrelated to thyroid dysfunction 2, 6

Step 3: Recheck Thyroid Function

• Monitor TSH and free T4 every 6-8 weeks while adjusting doses 5
• Target TSH within reference range (0.5-4.5 mIU/L) with normal free T4 5
• Approximately 25% of patients on levothyroxine are unintentionally maintained on doses sufficient to fully suppress TSH, increasing risk of hair loss and other complications 5, 7

Tirzepatide and Hair Loss

No evidence exists in the provided literature linking tirzepatide to hair thinning or loss. The available evidence focuses exclusively on thyroid-related medications and their effects on hair. Tirzepatide, a GLP-1 receptor agonist used for diabetes and weight management, operates through entirely different mechanisms than thyroid hormones and is not documented to affect hair follicle cycling.

Critical Pitfalls to Avoid

• Never assume hair loss in a hypothyroid patient is from levothyroxine without checking TSH levels first 5, 1
• The hair loss may be from inadequate treatment rather than the medication itself 3, 4
• Do not discontinue levothyroxine due to early hair loss without confirming overtreatment, as this temporary side effect usually resolves 1
• Stopping treatment will worsen hypothyroidism-related hair loss 3, 4
• Recognize that drug-induced hair loss is usually reversible after dose adjustment or interruption of treatment 2

Special Considerations for Patients with Thyroid History

For patients with a history of thyroid issues experiencing hair loss on levothyroxine:

• Hashimoto's thyroiditis patients may have experienced initial hair loss during the hypothyroid phase 5
• Hair loss should improve with adequate thyroid hormone replacement targeting TSH 0.5-4.5 mIU/L 5
• If hair loss persists despite normal TSH, consider checking vitamin B12 levels, as autoimmune thyroid disease patients should be screened periodically 5
• Overtreatment risks are substantial: approximately 25% of patients are inadvertently maintained on excessive doses causing iatrogenic hyperthyroidism with associated hair loss 5, 7

The key clinical principle: levothyroxine-induced hair loss is typically temporary and self-limited, while hypothyroidism-induced hair loss requires adequate treatment to resolve 1, 4.