Sobetirome (GC‑1)
Orally active, selective thyroid hormone receptor beta (TRβ) agonist thyromimetic (research code: GC-1). Binds selectively to TRβ-1 (EC50 ~0.16 μM), sparing the cardiac TRα, aims to mimic the beneficial metabolic/lipid effects of T3 without the typical hyperthyroid cardiac side effects. INVESTIGATIONAL: completed Phase 1 (~2008); Phase 2 was NOT conducted for the metabolic indication.
WHAT IS SOBETIROME (GC-1)?
Detailed overview
Sobetirome (research code: GC-1) is an orally active, selective thyroid hormone receptor beta (TRβ) agonist – a so-called thyromimetic. It binds selectively to the TRβ-1 receptor (EC50 ~0.16 μM) while sparing the cardiac TRα receptor. Thanks to this selectivity, Sobetirome aims to mimic the beneficial metabolic and lipid-lowering effects of thyroid hormone (T3) without the typical hyperthyroid (thyroid-overactivity) cardiac side effects. Clinical status: Sobetirome completed Phase 1 trials (~2008) that showed lipid-lowering effects with both single and multiple dosing; Phase 2 was NOT conducted for the metabolic indication. The compound was studied alongside other TRβ agonists – resmetirom (MGL-3196), VK2809, eprotirome – for dyslipidaemia and NASH/MASH (fatty liver disease). Documented effects: it lowers LDL-cholesterol and lipoprotein(a), and stimulates steps of reverse cholesterol transport (shown in primate preclinical studies). It modulates genes for cholesterol and fatty-acid biosynthesis/metabolism. Fat-loss relevance: a TRβ-selective thyromimetic raises hepatic lipid handling and metabolic rate (lipid oxidation) more safely than full T3. A CNS-penetrant prodrug of the molecule, Sob-AM2, has also been studied for myelin/CNS indications (X-linked adrenoleukodystrophy, demyelination, MCT8 deficiency) – meaning the molecule's TRβ agonism has been explored beyond metabolism. STATUS FRAMING: investigational / research compound, NOT an approved drug; available on the research-chemical market with label-claim/purity caveats. Honest about the thyromimetic risks: suppression of the HPT axis (hypothalamic-pituitary-thyroid), potential bone/muscle effects at high doses, and NOT for anyone with thyroid disease without medical supervision.
Mechanism
Selective TRβ-agonist thyromimetic (thyroid hormone receptor beta), spares the cardiac TRα
Binding selectivity
TRβ-1 EC50 ~0.16 μM (selective vs. cardiac TRα)
Clinical status
Phase 1 completed (~2008, lipid-lowering effect); Phase 2 NOT conducted for the metabolic indication
Documented effects
LDL-cholesterol + lipoprotein(a) lowering, reverse cholesterol transport stimulation (primate preclinical)
Legal status
Investigational / research compound, NOT an approved drug (FDA + EMA never approved); available on the research-chemical market
Data console
Lab data
Safety
Side effects, stop signs, contraindications
Side effects · 6
- Investigational compound with limited human safety data: only a closed Phase 1 (~2008), no Phase 2 for the metabolic indication, so the side-effect profile is poorly characterized.
- HPT-axis (hypothalamus-pituitary-thyroid) suppression: thyromimetic signaling can downregulate TSH and the body's own thyroid hormone production.
- Thyroid hormone excess (thyrotoxicosis-like) symptoms on overdose: palpitations, tachycardia, sweating, heat intolerance, irritability, weight loss, even though TRβ-selectivity aims to spare cardiac TRα.
- Risk of bone and muscle loss at high doses: chronic thyroid hormone excess is a known driver of bone loss (osteoporosis) and muscle catabolism; long-term human data have not excluded this for sobetirome.
- Possible thyromimetic side effects uncharacterized beyond Phase 1: fatigue, mood changes, GI symptoms (diarrhea) that can accompany accelerated thyroid-hormone-driven metabolism.
- Contamination and under/over-dosing risk from research-chemical sourcing: never FDA/EMA approved, so no pharmaceutical-grade product exists; declared content may be HPLC-unverified.
Contraindications · 6
- Pregnancy and breastfeeding: thyroid hormone signaling is critical for fetal and infant development (especially the nervous system); disrupting it carries teratogenic/developmental risk, so it must be strictly avoided.
- Any thyroid disease (hyper- or hypothyroidism, Graves', nodular goiter) without medical supervision: the thyromimetic load affects the axis unpredictably.
- Pre-existing cardiovascular disease (arrhythmia, coronary artery disease, heart failure): although TRβ-selectivity aims to spare cardiac TRα, long-term human cardiac safety data are lacking.
- Osteoporosis or high fracture risk: thyroid hormone excess accelerates bone loss, which can worsen in these patients.
- Concurrent thyroid hormone replacement (levothyroxine/T4 or liothyronine/T3): additive TRβ signaling and hyperthyroid risk; combine only under close medical supervision with thyroid monitoring (TSH, fT3, fT4).
- Competitive athletes: although sobetirome is not explicitly on the WADA prohibited list, the non-approved status can trigger the 'S0 catch-all non-approved substance' clause; NADA consultation advised.
Related Performance Compounds
Same therapeutic category
Studies
Related research and clinical findings
Maternal Administration of the CNS-Selective Sobetirome Prodrug Sob-AM2 Exerts Thyromimetic Effects in Murine MCT8-Deficient Fetuses
Valcárcel-Hernández V, Guillén-Yunta M, Scanlan TS, Bárez-López S et al.
Promyelinating drugs promote functional recovery in an autism spectrum disorder mouse model of Pitt-Hopkins syndrome
Bohlen JF, Cleary CM, Das D, Sripathy SR et al.
Sobetirome rescues α-synuclein-mediated demyelination in an in vitro model of multiple system atrophy
Mészáros L, Himmler M, Schneider Y, Arnold P et al.
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