Will my eyebrows grow back too?

Often they do. Thinning of the outer eyebrows is a known sign of hypothyroidism, and it tends to improve with the rest of the hair once levels are normal. Eyebrow hair also grows in cycles, so recovery takes months.

Why is my hair falling out more after starting levothyroxine?

Hairs pushed into the resting phase while you were untreated can shed months later, even after treatment starts. The Synthroid label also notes rare, usually temporary partial hair loss in the first few months. If shedding continues, ask for a blood test to check whether your dose is too high.

Should I switch to a different thyroid medicine to stop hair loss?

Not on your own. Hair loss on levothyroxine is more often about dose or another cause than about the specific pill. Talk with your clinician, who can check your levels and look for other reasons.

Does hair texture go back to normal on treatment?

Coarse, dry, brittle hair is a common feature of low thyroid hormone. Many people see texture improve as their levels normalize and new hair grows in. The change is gradual because the old hair has to be replaced.

When should I see a dermatologist?

See one if you have round bald patches, loss of eyelashes, a scalp that is itchy or scarred, or thinning that continues after several months of normal thyroid tests. These can point to alopecia areata or another condition that needs its own treatment.

Will Hair That Fell Out From Hypothyroidism Grow Back on Levothyroxine?

The short answer: Usually, yes. Hair thinning from an underactive thyroid tends to reverse once levothyroxine brings your levels back to normal. The American Academy of Dermatology says treating the thyroid disease can reverse the hair loss. Expect it to take months, not weeks, because hair grows on a slow cycle. If thinning continues after your levels have been normal for a while, look for a second cause.

How does hypothyroidism affect your hair?

Thyroid hormone acts directly on the hair follicle. In a 2008 lab study in the Journal of Clinical Endocrinology and Metabolism, T4 prolonged the growth phase of human scalp follicles and increased cell growth in the hair root. When hormone levels fall, that support drops too.

The changes people notice are fairly typical. A 2023 review in Cureus describes slow-growing, coarse, dry, brittle hair in hypothyroidism. It also lists diffuse thinning across the scalp and loss of the outer third of the eyebrows. The same review cites hair loss in about 33% of people with hypothyroidism. MedlinePlus lists thin, brittle hair among common symptoms and thinning eyebrows as a later sign.

The pattern matters. Thyroid-related loss is usually spread evenly over the scalp, not in round bald patches. For the full list of symptoms, see our guide to hypothyroidism warning signs.

Does levothyroxine make hair grow back?

In most cases it does, once your dose is right. MedlinePlus says that when levothyroxine is taken correctly, it reverses the symptoms of low thyroid hormone, and it names hair loss among them. The 2023 Cureus review adds that replacement therapy often halts the hair loss. It notes one exception: follicles that have wasted away after long-standing, untreated hypothyroidism may not fully recover.

The key word is "correct." Hair recovers when your thyroid levels are back in range and stay there. The Synthroid label says the peak effect of a given dose may take 4 to 6 weeks. It advises dose changes every 6 to 8 weeks in some adults until levels are normal. So the first few months are often spent finding the right dose. Hair regrowth usually starts only after that. Our levothyroxine guide covers how that dose-finding process works.

How long does it take for hair to grow back?

Most people should plan on several months. Each hair follicle runs on a cycle: a long growth phase, a short transition phase, and a resting phase. The 2023 review puts the resting phase at 2 to 3 months, after which the old hair falls out and a new one starts.

This creates a delay in both directions. A 2015 review of telogen effluvium in the Journal of Clinical and Diagnostic Research notes that diffuse shedding starts 3 to 4 months after a trigger. So hairs that were pushed into rest while you were untreated can keep falling out after treatment begins. New hairs then need time to grow long enough to see.

For shedding after illness or stress, the AAD says most people regain normal fullness within 6 to 9 months after the shedding stops. No study we found gives a precise timeline for thyroid-related loss. A reasonable way to think about it: the clock starts when your levels are stable, not on the day you fill the prescription.

Can levothyroxine itself cause hair loss?

It can, but the label calls it rare and usually temporary. The patient counseling section of the FDA-approved Synthroid label reads: "partial hair loss may occur rarely during the first few months of SYNTHROID therapy, but this is usually temporary." The current label does not limit that statement to children. MedlinePlus also lists hair loss as a side effect to report if it is severe or does not go away.

The label lists a second link. Its adverse reactions are mainly those of hyperthyroidism from too high a dose, and "hair loss" appears in that list. So hair loss on levothyroxine can mean two different things:

Early shedding in the first few months, which usually settles on its own.
Overtreatment, where the dose is too high. A blood test shows this, usually as a suppressed TSH.

Do not stop or cut your dose on your own because of shedding. Untreated hypothyroidism is itself a cause of hair loss.

What else could explain hair that keeps falling out?

If your levels have been normal for several months and hair is still thinning, the thyroid may not be the whole story. The telogen effluvium review says finding the cause requires ruling out endocrine, nutritional, and autoimmune disorders. Common suspects include:

Iron deficiency. A review in the Journal of the American Academy of Dermatology found mixed evidence linking iron deficiency to hair loss. It notes that serum ferritin is used to confirm iron deficiency. Heavy periods, which are a hypothyroid symptom, are a common cause of low iron in premenopausal women.
Alopecia areata. This autoimmune condition causes patchy loss. A 2020 meta-analysis of 17 studies found thyroid disease was more common in people with alopecia areata (odds ratio 3.66). A 2019 meta-analysis found the link was mainly with thyroid antibodies, the kind seen in Hashimoto's thyroiditis.
Telogen effluvium from other triggers. Childbirth, surgery, illness, a crash diet, or major stress can each cause heavy shedding a few months later.
Hereditary thinning. Pattern hair loss is the most common cause of hair loss worldwide, per the AAD. It can show up alongside thyroid disease.

A dermatologist can often tell these apart by the pattern and a scalp exam. Ask your clinician whether your TSH and free T4 are in range and whether iron studies make sense.

What can you do while you wait for regrowth?

Take levothyroxine the same way each day. The label says to take it on an empty stomach, one-half to one hour before breakfast.
Keep it 4 hours apart from iron and calcium supplements and antacids, as the label directs.
Get your follow-up blood tests. Hair tends to track your levels, so a stable, normal TSH comes first.
Be careful with biotin "hair" supplements. The Synthroid label says to stop biotin at least 2 days before a TSH or T4 test because it can distort results. Look up the evidence on biotin and iron at supplements.md before you buy.
Be gentle with your hair. Avoid tight styles and harsh treatments while new growth comes in.
Take photos in the same light once a month. Slow regrowth is easier to see in pictures than in the mirror.

The bottom line

Hair lost to hypothyroidism usually grows back once levothyroxine brings your thyroid levels into range. The recovery is slow. Dose adjustment takes weeks to months, and the hair cycle adds several more months before you see fuller hair. Some shedding in the first few months of treatment is described on the label as rare and usually temporary. If thinning persists once your levels are stable, check for overtreatment, low iron, alopecia areata, or other causes.

Last updated: September 2026. This article is for informational purposes only and does not constitute medical advice. Talk with your clinician or a dermatologist about ongoing hair loss before you change your levothyroxine dose or start supplements.