Hair loss while taking levothyroxine is common, usually temporary, and in most cases not actually caused by the medication itself. The shedding you’re noticing is almost always a consequence of the thyroid imbalance that led you to need levothyroxine in the first place, or a short-lived side effect of your body adjusting to treatment. The good news: hair loss from hypothyroidism is fully reversible with proper thyroid hormone replacement.
Why You’re Losing Hair on Levothyroxine
Hypothyroidism triggers a type of shedding called telogen effluvium, where a large number of hair follicles shift into their resting phase at the same time. Instead of the normal cycle where only a small percentage of hairs rest and fall out on any given day, a much bigger batch enters that phase together, then sheds weeks later. This happens because your body didn’t have enough thyroid hormone to keep follicles actively growing.
Here’s where the timing gets confusing: when you start levothyroxine, your body may actually shed more hair during the first month or so. That’s because the medication wakes up dormant follicles. The old, weakened hairs get pushed out as new, healthier ones start growing underneath. Many people see this burst of shedding, blame the medication, and stop taking it. That’s the worst thing you can do, because discontinuing treatment lets the underlying hypothyroidism worsen and the hair loss continue.
Get Your Dose Right First
The single most important thing you can do to stop hair loss is reach and maintain the correct levothyroxine dose. Hair follicles are sensitive to thyroid hormone levels, and if you’re undertreated (your dose is too low) or your levels are swinging up and down because of inconsistent dosing or frequent adjustments, your hair will keep shedding. Stable, optimized thyroid levels are the foundation everything else builds on.
Take your levothyroxine the same way every day, ideally on an empty stomach 30 to 60 minutes before eating. Calcium, iron supplements, and coffee can all interfere with absorption if taken too close to your dose. Inconsistent absorption means inconsistent hormone levels, and that instability alone can prolong shedding. If your TSH levels have been bouncing around at recent blood draws, work with your prescriber to find a stable dose before assuming something else is causing the problem.
The Realistic Timeline for Regrowth
Hair doesn’t bounce back overnight. Once your thyroid levels stabilize in the normal range, most people notice shedding slows down within about two months. Visible regrowth, where you start seeing shorter new hairs coming in, typically takes four to six months. Full recovery of thickness and density can take closer to a year, because hair grows roughly half an inch per month and follicles need time to cycle back into their active growth phase.
This timeline frustrates a lot of people because it feels like nothing is changing. But if your levels are stable and the shedding has slowed, regrowth is already underway. You just can’t see it yet.
Nutrients That Support Hair During Treatment
Several nutrient deficiencies overlap with hypothyroidism and can worsen hair loss independently. Addressing them won’t replace proper levothyroxine dosing, but it removes additional barriers to regrowth.
- Iron and ferritin: Low iron stores are one of the most common causes of hair shedding in women and frequently coexist with hypothyroidism. If you haven’t had your ferritin (stored iron) checked recently, it’s worth asking for. Many people with “normal” iron levels still have ferritin low enough to contribute to hair loss. Just remember to take iron supplements at least four hours apart from levothyroxine, since iron blocks its absorption.
- Selenium: This mineral plays a direct role in thyroid function, and deficiency is linked to hair loss. In people with Hashimoto’s thyroiditis (the most common cause of hypothyroidism), selenium supplementation alongside levothyroxine has been shown to significantly reduce thyroid antibody levels within three months, with continued improvement at six and twelve months. Lower antibody levels suggest less ongoing damage to the thyroid gland, which helps stabilize hormone levels.
- Zinc: Zinc deficiency is associated with both thyroid dysfunction and hair loss. If your diet is low in meat, shellfish, or legumes, a modest zinc supplement may help. High-dose zinc over long periods can deplete copper, so moderation matters.
- Vitamin D: Deficiency is extremely common in people with hypothyroidism and has been independently linked to hair shedding. A simple blood test can tell you where you stand.
Be Careful With Biotin
Biotin is one of the most popular supplements marketed for hair health, and many people taking levothyroxine reach for it. There’s an important catch: biotin interferes with the blood tests used to measure thyroid hormones. It can make your results look artificially normal (or abnormal), which may lead your doctor to adjust your dose incorrectly. The American Thyroid Association recommends stopping biotin for at least two days before any thyroid blood work.
The evidence that biotin actually improves hair growth in people who aren’t biotin-deficient is thin. True biotin deficiency is rare. If you do take it, the timing around lab work is critical, because a misleading test result could keep you on the wrong dose for months, prolonging the very hair loss you’re trying to fix.
Protect the Hair You Have
While waiting for regrowth, minimizing mechanical damage keeps thinning less visible and prevents breakage that makes the problem look worse than it is.
Avoid tight ponytails, buns, and braids that pull on weakened follicles. Reduce heat styling or use a heat protectant when you do. Switch to a wide-tooth comb on wet hair instead of brushing, since wet hair is more elastic and more prone to snapping. Sulfate-free shampoos are gentler on fragile strands, and washing every other day rather than daily reduces the physical handling that loosens resting hairs prematurely.
Some people find that volumizing products or shorter haircuts create the appearance of fuller hair during the regrowth phase. These are cosmetic fixes, not medical ones, but they can make a real difference in how you feel while waiting for your follicles to catch up.
When Hair Loss Persists Despite Stable Levels
If your thyroid levels have been stable in the normal range for six months or more and you’re still losing hair at an unusual rate, something else may be contributing. Iron deficiency, hormonal changes (including perimenopause or postpartum shifts), stress-related telogen effluvium, and androgenetic hair loss (pattern thinning) can all overlap with thyroid-related shedding. These have different mechanisms and different treatments, so identifying the right cause matters. A dermatologist who specializes in hair loss can examine your scalp, check additional labs, and distinguish between these possibilities.