GC-1
Sobetirome
GC-1 (Sobetirome) is a metabolic & fat loss research compound. Thyroid-hormone receptor-β selective agonist — drives lipid burning and metabolic rate without the cardiac β1 effects of T3.
GC-1 quick facts
| Reported research dose | 100mcg-500mcg |
| Route | Oral |
| Frequency | 1x Daily AM · 5 On 2 Off or Daily |
| Half-life | ~several hours (long tissue retention) |
| Forms | Oral |
| Evidence level | Animal + early human |
Thyroid-β selectivity is the whole point — metabolic push with less heart stress. Still early.
How GC-1 works
Thyroid-hormone receptor-β selective agonist — drives lipid burning and metabolic rate without the cardiac β1 effects of T3.
Proposed benefits
Researched for fat oxidation, appetite and energy regulation, insulin sensitivity and endurance capacity.
Where to get GC-1
Buy GC-1 at Disguised Alpha →The evidence for GC-1
Graded by what exists behind each claim.
✅ Clinically validated
- Reached phase 2 in humans as sobetirome, for hypercholesterolemia — where it lowered LDL cholesterol and lipoprotein(a). Development did not continue to approval.
- Later work repurposed the scaffold for X-linked adrenoleukodystrophy, using a CNS-penetrant prodrug — a rare disease application quite unrelated to how it is sold in the research market.
📊 Correlative data
- Research-market use for fat loss, on the reasoning that it delivers thyroid hormone's metabolic effects without the cardiac ones. Reported experience includes suppression of the thyroid axis, which is what any thyroid receptor agonist does and is the thing people underestimate.
- Beyond that the record is self-reported: community dosing logs are real information about tolerability and almost none about efficacy.
🧪 Theoretical / extrapolated
- A selective thyroid hormone receptor beta agonist. The distinction carries the whole rationale: TRβ predominates in liver and drives cholesterol clearance and metabolic rate, while TRα predominates in heart and mediates the tachycardia and arrhythmia that make T3 dangerous for weight loss.
- The same TRβ logic produced resmetirom, which was approved for MASH in 2024 — so the mechanism is validated in humans, just not in this molecule.
- Selectivity is relative, not absolute. At high enough doses TRβ agonists hit TRα, and the axis suppression happens regardless of selectivity because the pituitary uses TRβ to sense thyroid status.
What community dosing logs are worth →
How to read these tiers: they say how much human evidence exists, not how well something works — and ✗ flags harm, never a disappointing trial. How the evidence tiers work →
What GC-1 actually does
There are two thyroid hormone receptors and they sit in different organs. That is the entire design of this molecule. TRβ1 is the dominant form in the liver, where it drives LDL receptor expression, cholesterol clearance and bile acid synthesis. TRα1 is the dominant form in the heart, where it drives the tachycardia and arrhythmia that make T3 unusable as a metabolic drug. GC-1 — sobetirome — is a synthetic thyromimetic built to selectively bind and activate TRβ over TRα Scanlan 2010 Lammel Lindemann 2016, so it should reach the liver receptor and leave the cardiac one alone.
And the cardiac half of that claim has a named gene behind it, which almost nobody quotes. Trost 2000 gave hypothyroid mice equimolar doses of GC-1 and T3. GC-1 produced better triglyceride-lowering and similar cholesterol-lowering than T3 — and then the separation: T3, but not GC-1, increased heart rate, and T3 raised HCN2 messenger RNA. HCN2 is a subunit of the hyperpolarization-activated pacemaker channel that sets the sinoatrial firing rate. So thyroid tachycardia is not a vague “stimulant” effect; it is transcriptional upregulation of a specific pacemaker channel through TRα, and a TRβ-selective agonist does not do it. That is as mechanistically clean as a selectivity claim gets.
Then the selectivity was quantified, and the numbers are the most useful thing on the page. Grover 2004 worked in cholesterol-fed rats and in cynomolgus monkeys. In rats GC-1 lowered cholesterol about 30 times more potently than it induced tachycardia — an ED50 of 190 nmol/kg for the lipid effect against an ED15 of 5,451 nmol/kg for heart rate. In monkeys, no tachycardia was observed for GC-1, unlike T3. But read the third number in that paper carefully, because it is the one that undercuts the sales pitch: GC-1 showed only approximately 10-fold selectivity for increasing metabolic rate over tachycardia. Thirty-fold for cholesterol. Ten-fold for metabolic rate. The lipid effect and the fat-burning effect are not the same dose, and they are not even close.
The selectivity that is not achievable is at the pituitary, and this is where people get caught. The pituitary thyrotroph senses circulating thyroid hormone through TRβ — the very receptor this drug is designed to hit. So a TRβ-selective agonist suppresses TSH by design, not as an off-target effect, and cardiac selectivity does nothing to protect against it. Axis suppression is the one consequence that follows from the mechanism working exactly as intended.
Cell, rodent, human — and where it stops
Step one, mice, and the comparison is equimolar. Hypothyroid mice given GC-1 or T3 at matched molar doses: better triglyceride-lowering, similar cholesterol-lowering, and no heart rate increase and no HCN2 induction on GC-1 Trost 2000.
Step two, rats and monkeys, seven days each. Grover 2004 dosed cholesterol-fed rats and cynomolgus monkeys for 7 days, producing the 30-fold cholesterol-versus-tachycardia separation and the absence of tachycardia in a primate. Two species, consistent direction.
Step three, and this is the result the marketing skips. Columbano 2006 gave rats GC-1 at 50 or 100 µg per 100 g body weight and found it strongly stimulates hepatocyte proliferation and induces massive pancreatic cell proliferation, with bromodeoxyuridine incorporation as the read-out and a rapid rise in cyclin D1 messenger RNA. Cyclin D1 is the G1/S checkpoint driver — this is cells being pushed into division, in two organs, by a compound sold for fat loss. It is not a toxicity finding in the usual sense; it is the receptor doing something nobody wanted.
Step four, humans, and it is thinner than people assume. The review of sobetirome’s own development reports that it progressed through preclinical animal studies and Phase I human clinical trials with excellent results and without obvious harmful side effects Lammel Lindemann 2016. Phase I. Not phase 3, not an efficacy program, and no published outcome data.
Step five, the class’s one large controlled trial, in a different molecule, and it stopped early. Sjouke 2014 — AKKA — randomized 236 patients with familial hypercholesterolemia to placebo (80), eprotirome 50 µg (79) or 100 µg (77). LDL cholesterol fell 12% (−28 to 4%) at 50 µg and 22% (−32 to −13%) at 100 µg against placebo. The trial was prematurely terminated at 6 weeks when another study found eprotirome causes cartilage damage in dogs, and in the trial itself there were statistically significant increases in AST, ALT, conjugated bilirubin and gamma-glutamyltransferase. The review of sobetirome names both concerns explicitly — fears of thyrotoxic effects in the heart and the emergence of cartilage defects in dogs after long-term use of eprotirome Lammel Lindemann 2016.
The obstacle, stated exactly. The mechanism is real and it has since been validated in humans by a different molecule reaching approval — but not by this one, and the two adverse findings that matter came from long-term dosing rather than from the short studies that produced the good numbers. Every favorable GC-1 result above ran for seven days Grover 2004. The proliferation finding Columbano 2006 and the cartilage and liver findings Sjouke 2014 are what appear when the exposure is extended. Nobody has run GC-1 in a human for long enough to know which category it falls into, and the compound as sold is taken for 4 to 16 weeks.
GC-1 pharmacokinetics — how much of it actually gets in
Route: oral, and the tissue-selectivity claim is partly a distribution claim rather than a receptor claim. Sobetirome is described as having tissue-selective thyromimetic properties with preferential hepatic accumulation Scanlan 2010 Lammel Lindemann 2016. That matters: some of the cardiac sparing is the molecule not reaching the heart in quantity, rather than the receptor refusing to bind it — and a distribution-based selectivity is the kind that erodes as the dose rises.
What degrades it: not published for this molecule. There is no CYP assignment, no human clearance fraction, no metabolite identification and no published human half-life for sobetirome. What is known about disposition is the hepatic uptake preference above. That absence is itself a finding: interactions with anything else being taken cannot be reasoned about, and the half-life that would set the dosing interval has never been measured in a person.
The oral barrier and the one hard human statement. The molecule is a small carboxylic-acid thyromimetic and it is dosed orally throughout its literature; the review confirms it reached Phase I human trials Lammel Lindemann 2016, which means human pharmacokinetics were generated — they were simply never published in a form this page can cite. The closest published human exposure–response data for the class comes from the 50 and 100 µg eprotirome arms of AKKA Sjouke 2014, which is a different molecule and cannot be converted into a sobetirome dose.
The arithmetic, done out loud, because it is the only way to size the vault dose against anything. The proliferation dose in rats was 50–100 µg per 100 g, which is 0.5–1 mg/kg Columbano 2006. Converting by the standard body-surface-area factors (rat 6, human 37) gives a human-equivalent dose of roughly 80–160 µg/kg, or about 5.7–11 mg for a 70 kg adult. Set that against the 100–500 µg this site records and the vault dose is roughly 11 to 110 times below the scaled proliferative dose. That is genuinely reassuring on its face — and it is a milligram-per-kilogram conversion applied to a nuclear receptor agonist, where the effect depends on receptor occupancy rather than on body surface area, and where nobody has measured occupancy in either species. Treat it as a bound, not a clearance.
What would have to be true, and how you would know it was not
Four predictions. The first two are the on-target effects, the third is the one people underestimate, and the fourth argues that the reason most people take this compound is the wrong reason.
1. The lipid panel should move, and it should move first. Hepatic TRβ activation raises LDL receptor expression, so run a lipid panel, ApoB and Lp(a) at baseline and at 6 weeks. The class benchmark to beat is eprotirome’s 22% LDL reduction at 100 µg Sjouke 2014. If ApoB has not moved at 6 weeks, the compound is not engaging hepatic TRβ at that dose, and nothing else on this page is going to be happening either.
2. TSH should be suppressed, and free T4 should follow it down. Draw TSH and free T4 at baseline, 4 weeks and 8 weeks. This is not a side effect to watch for — it is the mechanism, because the pituitary senses thyroid status through the same TRβ the drug is built to hit. The falsifiable claim is sharp: a TRβ agonist that leaves TSH untouched is not reaching its receptor. And the corollary matters more than the test: suppressed TSH with a falling free T4 is drug-induced central hypothyroidism, and the axis does not necessarily restart the day the compound stops.
3. Resting heart rate should NOT rise, and this is the selectivity test. Take a resting morning heart rate for 14 days before starting and continuously afterwards. Trost 2000 found no heart-rate increase and no HCN2 induction on GC-1 where T3 produced both; Grover 2004 found no tachycardia in monkeys and a 30-fold separation in rats. A climbing resting heart rate therefore means the TRα margin has been crossed — which is a dose statement, not a tolerance statement, and the response the data support is stopping rather than adjusting.
4. The prediction that cuts against the reason people buy it: at a dose that moves lipids, body weight should barely move. Grover 2004 measured both and the selectivity ratios differ by threefold — 30-fold for cholesterol lowering versus tachycardia, about 10-fold for increasing metabolic rate. In plain terms the metabolic-rate effect needs a substantially higher dose than the lipid effect, and it sits closer to the cardiac one. So the honest prediction is that a dose safe enough to avoid tachycardia will produce a clear ApoB fall and an unimpressive weight change, and anybody who escalates until the scale moves is walking the margin down deliberately. Log weight weekly against the 6-week ApoB draw and the two curves should visibly disagree.
What nobody has tested yet
Nobody has published a human pharmacokinetic profile for sobetirome. Phase I trials were run Lammel Lindemann 2016, so the data exist somewhere, but there is no citable human half-life, no clearance route and no exposure–response curve. Without a half-life the dosing interval is guesswork, and for a nuclear receptor agonist — where the effect is transcriptional and outlasts the plasma concentration — that guesswork runs in the direction of accumulation.
Nobody has checked whether the rat proliferation finding happens in a primate. Columbano 2006 is the single most important negative fact about this molecule and it exists in one species. Grover 2004 already dosed cynomolgus monkeys for seven days for cardiac endpoints — the proliferation question needs the same design with a longer duration and a liver and pancreas BrdU or Ki-67 read-out. It has never been reported.
Nobody has established whether the cartilage signal is a class effect or a molecule effect. Eprotirome caused cartilage damage in dogs and that finding stopped a phase 3 trial in humans Sjouke 2014 Lammel Lindemann 2016. Whether sobetirome does the same thing has not been published. The two molecules share a target and not a structure, so the question is genuinely open, and it is the kind of finding that only appears with long dosing — which is exactly the exposure pattern of somebody running a 16-week cycle.
And nobody has measured how long the thyroid axis takes to recover. Suppressing TSH through pituitary TRβ is the predictable consequence of the mechanism, and yet there is no published time course of TSH and free T4 recovery after stopping a TRβ agonist in a human. That is a series of blood draws over eight weeks in a handful of people, it is the question most likely to affect somebody who used this compound, and the literature has nothing to say about it.
GC-1 — its own safety story, not its class's
The proliferation finding comes first, because it is specific to this molecule and it is not in any class safety block. Columbano 2006 reports that GC-1 strongly stimulates rat hepatocyte proliferation and induces massive pancreatic cell proliferation, with a rapid rise in cyclin D1, at 50–100 µg per 100 g body weight. Two organs, driven into the cell cycle. It has not been shown to cause tumors and it has not been shown not to; what it establishes is that this receptor, in this tissue, at that exposure, is a growth signal. Nothing about the thyroid-selectivity argument addresses it, because the proliferation is happening in the liver — the organ the drug was designed to reach.
The class’s human safety signals, from the one large controlled trial that exists. AKKA was stopped early, and it was stopped for a dog finding rather than a human one: cartilage damage in dogs on long-term eprotirome Sjouke 2014. Inside the trial itself, the human signal was hepatic — statistically significant increases in AST, ALT, conjugated bilirubin and GGT. Conjugated bilirubin rising alongside the transaminases is a more serious pattern than an isolated ALT bump, and it appeared within a trial that ran only six weeks before termination.
Thyroid axis suppression is not a risk of overdosing — it is what success looks like. The pituitary reads thyroid status through TRβ, so TSH falls whenever the drug is working. Someone who stops after a 16-week cycle can have a suppressed axis with a low free T4 and the symptoms of hypothyroidism while their own thyroid output recovers, and no published data says how long that takes. A TSH and free T4 drawn before starting is the only way to know afterwards what normal looked like.
What is genuinely reassuring, and it is worth stating precisely. The cardiac sparing is real and quantified: no heart rate rise at equimolar T3 doses in mice with no HCN2 induction Trost 2000, a 30-fold potency separation in rats and no tachycardia in monkeys Grover 2004, and Phase I human trials without obvious harmful side effects Lammel Lindemann 2016. That is a better cardiac safety story than T3 has, and it is the one claim for this compound that the data actually support. It is also, on its own, an argument about the heart — not about the liver, the pancreas, the cartilage or the pituitary.
Sources read for this page
- Scanlan TS. Sobetirome: a case history of bench-to-clinic drug discovery and development.. Heart Fail Rev 2010 · PMID 19002578
- Lammel Lindemann J, Webb P. Sobetirome: the past, present and questions about the future.. Expert Opin Ther Targets 2016 · PMID 26565124
- Trost SU, Swanson E, Gloss B, Wang-Iverson DB, Zhang H, Volodarsky T, Grover GJ, Baxter JD, Chiellini G, Scanlan TS, Dillmann WH. The thyroid hormone receptor-beta-selective agonist GC-1 differentially affects plasma lipids and cardiac activity.. Endocrinology 2000 · PMID 10965874
- Grover GJ, Egan DM, Sleph PG, Beehler BC, Chiellini G, Nguyen NH, Baxter JD, Scanlan TS. Effects of the thyroid hormone receptor agonist GC-1 on metabolic rate and cholesterol in rats and primates: selective actions relative to 3,5,3'-triiodo-L-thyronine.. Endocrinology 2004 · PMID 14701670
- Columbano A, Pibiri M, Deidda M, Cossu C, Scanlan TS, Chiellini G, Muntoni S, Ledda-Columbano GM. The thyroid hormone receptor-beta agonist GC-1 induces cell proliferation in rat liver and pancreas.. Endocrinology 2006 · PMID 16574785
- Sjouke B, Langslet G, Ceska R, Nicholls SJ, Nissen SE, Ohlander M, Ladenson PW, Olsson AG, Hovingh GK, Kastelein JJ. Eprotirome in patients with familial hypercholesterolaemia (the AKKA trial): a randomised, double-blind, placebo-controlled phase 3 study.. Lancet Diabetes Endocrinol 2014 · PMID 24731671
GC-1 — safety, predicted from mechanism
Predicted from mechanism, not from a human safety trial. How that reasoning works →
What the mechanism predicts
Derived from the molecule, not a trial.
- Beta-2 agonists (clenbuterol, albuterol) and central stimulants (tesofensine) share one predicted problem: cardiac load. Raised heart rate, palpitations, tremor and insomnia are the mechanism showing up, not an idiosyncratic reaction.
- Beta-2 agonists drive potassium into cells, so hypokalemia is predicted — and low potassium is itself arrhythmogenic, which is how a stimulant side effect becomes a cardiac one.
- Clenbuterol's half-life is long (well over a day in humans), so it accumulates across daily dosing. The dose that felt fine on day one is not the exposure you have on day five.
- Beta-2 receptors downregulate within around two weeks — the thermogenic effect fades while the cardiac effect persists longer. That is the worst possible combination and it is why escalating the dose to chase the original effect is the dangerous move.
What has actually been reported
- Cardiac hypertrophy is documented in animal models at sustained high doses. Human data comes largely from poisoning case reports — tachycardia, tremor, hypokalemia, and arrhythmia.
- Tesofensine raised blood pressure and heart rate in trials, which is part of why its development for obesity stalled.
How to reduce the risk
Same mechanism as the prediction.
- Take a resting heart rate every morning. It moves before anything else does and it is a better early signal than any quarterly panel.
- Potassium and magnesium intake matter here specifically because of the intracellular shift — this is one of the few places a supplement addresses the actual mechanism rather than a vague deficiency.
- Do not escalate to recover a faded effect. The fade is receptor downregulation, and the answer is a break, not more.
What it does to your bloodwork
A fact about the assay.
- Potassium and magnesium (a CMP covers potassium). Blood pressure and resting heart rate are the real monitoring and they are free.
Don't run this if
- You have any arrhythmia, structural heart disease, or uncontrolled hypertension.
- You are already taking another stimulant, including high-dose caffeine — the cardiac effects are additive and people do not count coffee.
The honest unknown
- Whether the cardiac hypertrophy seen in animals occurs at the doses and durations used in humans is not established, and it would be difficult to study ethically.
Not medical advice. If you take prescription medication or have a diagnosed condition, check this with a pharmacist or doctor.
GC-1 — interference & stacking
Predicted from mechanism, not from an interaction study. How mechanism-predicted claims are made →
What GC-1 moves on your bloodwork
Expected direction, not a measured one.
- TSH (Thyroid-Stimulating Hormone) — ↓ expected to fall
Exogenous thyroid hormone or a thyromimetic suppresses TSH by feedback. A suppressed TSH here is the expected consequence, not evidence of thyroid disease.
What to do: TSH alone is uninterpretable on these. Run free T3 and free T4 with it or the panel means nothing. - Free T3 (Triiodothyronine) — ↑ expected to rise
Rises with dosing, and this is the number driving both the benefit and the risk.
What to do: The gap between 'metabolically effective' and 'losing muscle and beating up your heart' is narrow. Test, don't estimate. - Complete Blood Count (CBC) with Differential — ◆ worth watching
Not the marker itself — but resting heart rate and blood pressure are the real-time readouts of over-dosing here, and they move before any lab does.
What to do: Take a resting heart rate every morning. It is a better early signal than a quarterly panel. - Comprehensive Metabolic Panel (CMP) — ◆ worth watching
Uncouplers and strong thermogenics raise metabolic demand and can stress liver enzymes.
What to do: Baseline liver function before, and again at 8 weeks.
- How to work up to it, and when not to
- When to take it, and why that window
- Cycle length
- Time off between cycles
- Fasted or fed, and when in the day
- Coach Cam's personal notes
- Which compounds push the same lever, and why the dose adds up faster than people count
- What blunts it — the stacks that waste your money
- What compounds the risk, so a side effect arrives sooner than any one of them suggests
- Coach Cam's read on running it alongside the rest of your protocol
Everything above is free and stays free. Skool is where it becomes a plan — GC-1 in an order, with the rest of what you're running.
Unlock in Skool — $10/mo →Bloodwork to run alongside GC-1
Baseline first, then again at 8–12 weeks.
| Marker | What it’s watching for |
|---|---|
| HbA1c (Hemoglobin A1c) | Where you started, so you can prove the change was real |
| Fasting Insulin | Moves years before HbA1c does — the earliest signal you get |
| Lipid Panel (Cholesterol, HDL, LDL, Triglycerides) | Rapid fat loss shifts triglycerides fast, in both directions |
| Comprehensive Metabolic Panel (CMP) | Liver, kidney and electrolytes while intake is restricted |
The Metabolic Health & Prediabetes panel covers these in one order — 8 markers, $81.45 with the discount applied.
Check results you already have → · All 103 markers A–Z
GC-1 — frequently asked questions
What is GC-1?
GC-1 (Sobetirome) is a metabolic & fat loss research compound. Thyroid-hormone receptor-β selective agonist — drives lipid burning and metabolic rate without the cardiac β1 effects of T3.
Is the full GC-1 protocol on this page?
The reported research dose is on this page, along with how GC-1 works and the evidence behind it. The protocol — how to work up to it, frequency, cycle length, time off, what not to stack it with and Coach Cam's notes — is inside Skool.
What is the half-life of GC-1?
GC-1 has an approximate half-life of ~several hours (long tissue retention), which is part of what determines how often it's dosed.
What's the evidence behind GC-1?
Current evidence level: Animal + early human. GC-1 is offered for research purposes only and is not an approved medicine.
GC-1 inside a finished plan
One arm of 2 Protocol Blueprints, free to read in full.
What GC-1 is used for
GC-1 appears under 2 goals in the goal router.
Related Metabolic & Fat Loss compounds
Where this goes next
GC-1 is the thyroid-substrate arm of this plan. The page above is the free breakdown of one compound; the plan it belongs to — the dosing, the order to correct things in, the week-by-week schedule and what to retest — is a lesson inside Skool.