Cytomel (Liothyronine) Hair and Skin Changes: What T3 Actually Does to Your Integument

Does liothyronine cause hair loss?

The Cytomel label puts hair loss in its dermatologic list, next to flushing [1]. It introduces that list by saying the reactions are primarily those of hyperthyroidism due to therapeutic overdosage [1]. Read plainly, the label places hair loss in the overdosage picture.

The label also warns that the drug has a narrow therapeutic index. It says over- or undertreatment can affect growth and development, cardiovascular function, bone metabolism, reproductive function, cognitive function, emotional state, gastrointestinal function, and glucose and lipid metabolism [1]. Hair and skin are not named in that warning.

What the label says about skin

Flushing is the other dermatologic reaction listed with hair loss [1]. The label also has a hypersensitivity section: reactions to inactive ingredients have included urticaria, pruritus, skin rash, flushing, angioedema, abdominal pain, nausea, vomiting, diarrhea, fever, arthralgia, serum sickness and wheezing [1]. The label's list of most common adverse reactions ends with skin rash [1].

What hypothyroidism does to skin

Generalized myxedema is still the classic cutaneous sign of hypothyroidism. It comes from deposition of dermal acid mucopolysaccharides, notably hyaluronic acid, and the skin does not pit with pressure despite its appearance [2].

At the epidermal level, normal human epidermis makes TSH and transcribes the TSH receptor. Intraepidermal TSH is increased by TRH and decreased by thyroid hormones. Treating organ-cultured human scalp skin with TSH increased expression of involucrin, loricrin and keratins 5 and 14 [3]. That is laboratory work on cultured skin, not a clinical measurement in people taking liothyronine.

Myxedema coma is a separate emergency. The label says oral thyroid hormone products are not recommended to treat it and that intravenous products should be used [1].

Do trials of T3 show any hair or skin benefit?

Fourteen clinical trials had not shown a consistent benefit of levothyroxine plus liothyronine over levothyroxine alone [4]. An 11-trial meta-analysis of 1,216 adults found no difference in bodily pain, depression, anxiety, fatigue, quality of life, body weight or lipids, and adverse events did not differ [5]. Hair and skin are not among the outcomes it lists.

Bunevicius et al. (New England Journal of Medicine, 1999) studied 33 adults with hypothyroidism over two five-week periods in randomized order. In one period they took their usual thyroxine. In the other, 50 mcg of thyroxine was replaced with 12.5 mcg of liothyronine. Six of 17 cognitive and mood scores and 10 of 15 visual-analogue scales were better or closer to normal on the combination. Pulse rate and sex hormone-binding globulin were slightly higher, while blood pressure, lipids and neurophysiologic tests were similar [6]. The abstract reports no hair or skin outcome.

Is T3 with levothyroxine approved, and is it recommended?

The label describes Cytomel as replacement therapy for hypothyroidism. When switching a patient, it says to discontinue levothyroxine and start Cytomel at a low dose, increasing gradually [1]. The label does not describe a levothyroxine plus liothyronine regimen, so combining the two is off-label.

The American Thyroid Association's 2014 guideline kept levothyroxine as the standard of care. It recommended against routine combination therapy (weak recommendation, moderate-quality evidence) and said the evidence was insufficient to support a routine trial of combination therapy outside a formal trial or an N-of-1 trial [7]. A 2023 joint statement from the British Thyroid Association and the Society for Endocrinology said a trial of combined therapy may be warranted for some patients with confirmed overt hypothyroidism and persistent symptoms despite optimized levothyroxine, as a shared decision [8]. A 2021 ATA/BTA/ETA consensus found equipoise for a new trial and proposed a design for one [4].

What to watch for

The label's overdosage section lists the signs and symptoms of hyperthyroidism plus confusion and disorientation. It notes that cerebral embolism, seizure, shock, coma and death have been reported, and that symptoms may not appear until several days after ingestion [1]. The label directs overdose questions to the National Poison Control Center at 1-800-222-1222 [1].

Where the evidence stops

Neither the label nor the studies cited here tie liothyronine to hair density, shedding counts or skin quality, in either direction. The label also has no statement about taking Cytomel on an empty stomach, with coffee, or about biotin interfering with thyroid lab tests [1]. For the absorption interactions it does cover, bile acid sequestrants and ion exchange resins, the label says to give Cytomel at least 4 hours before them or to monitor TSH [1].