Hair changes on Synthroid: thinning, loss, regrowth
Medication-related hair changes are a common cause of distress and a frequent reason for switching therapy. Synthroid (Levothyroxine) at 25mcg, 50mcg, 75mcg, 100mcg, 150mcg may or may not affect hair depending on Levothyroxine; this page summarises the typical pattern, the timeline and what can be done short of stopping the medication.
Hair effects of Synthroid
Medications can cause hair thinning through telogen effluvium (a delayed shedding 2–4 months after a stressor), direct interference with hair-cycle hormones, or accelerated growth-phase termination. Conversely, some medications stimulate hair regrowth as a primary or secondary effect. Whether Levothyroxine affects hair, and in which direction, is in the prescribing information. Levothyroxine replaces deficient endogenous thyroxine, which is converted in tissues to the active hormone triiodothyronine (T3) by deiodinase enzymes.
Practical guidance
According to dermatology practice, mild medication-induced hair thinning typically stabilises within months and reverses partially or fully on stopping the trigger. The decision to continue Synthroid at 25mcg, 50mcg, 75mcg, 100mcg, 150mcg despite hair changes is individual: the underlying condition's severity, the alternatives and the patient's tolerance all weigh in. Topical minoxidil, nutritional review and dermatology consultation are reasonable adjuncts.
Frequently asked questions
Will Synthroid cause hair loss? ▾
For some users, yes — the prescribing information for Levothyroxine lists hair-related side effects when documented. Most medication-induced hair thinning is mild, gradual and reversible. Sudden severe hair loss is uncommon and warrants prompt review with the prescriber.
Will my hair grow back after stopping Synthroid? ▾
For most users, yes — medication-induced hair changes typically reverse over months after stopping the trigger, though full restoration can take 6–12 months. Other causes (genetic pattern, thyroid, iron deficiency) may also contribute and should be evaluated if hair does not recover.
More on Synthroid
- With alcoholSynthroid and alcohol — is it safe to drink?
- With foodShould Synthroid be taken with food?
- Side effectsSynthroid side effects: common, rare and warning signs
- Dosage guideSynthroid dosage guide: how much to take and when
- OnsetHow fast does Synthroid start working?
- DurationHow long does Synthroid last?
The information on this website is provided for reference and educational purposes only. It does not replace consultation with a qualified healthcare professional.