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Thyroid hormones (T3 / T4)

Liothyronine / Cytomel / T3, Levothyroxine / Synthroid / T4, Sobetirome / GC-1 · Thyroid hormone (metabolic)

Research reference only. Pepdex does not sell, supply or track this compound, and nothing here is guidance to use it — this page exists so the evidence and the risks are visible.

What it is

Prescription thyroid hormones — levothyroxine (T4) and liothyronine (T3) — taken without thyroid disease in an attempt to raise metabolic rate during diets. Unapproved thyromimetics like GC-1 (sobetirome) circulate under the same umbrella.

What human evidence shows

The metabolic effect is textbook endocrinology. Historical studies in euthyroid people exist, but they do not establish an acceptable benefit-risk profile for weight loss — hyperthyroid states burn muscle alongside fat.

Risks

Excess exogenous thyroid hormone can cause iatrogenic thyrotoxicosis: muscle catabolism (a meaningful share of the weight lost is tissue you wanted to keep), bone-density loss, arrhythmia and cardiac strain, heat intolerance, anxiety. Exogenous hormone suppresses your own axis; transient suppression and hypothyroid-pattern symptoms can follow stopping, with recovery time varying. Unapproved thyromimetics add unknown-compound risk on top.

Stacking interactions

Documented interactions with other things people research. A compound not listed here does not mean the combination is safe — only that no specific interaction is on file.

CautionClenbuterol

Concurrent exposure to agents with sympathomimetic cardiovascular effects may further increase heart rate, blood pressure, or arrhythmia risk; pair-specific evidence varies.

CautionAdderall

Concurrent exposure to agents with sympathomimetic cardiovascular effects may further increase heart rate, blood pressure, or arrhythmia risk; pair-specific evidence varies.

CautionDMAA

Concurrent exposure to agents with sympathomimetic cardiovascular effects may further increase heart rate, blood pressure, or arrhythmia risk; pair-specific evidence varies.

CautionTesofensine

Concurrent exposure to agents with sympathomimetic cardiovascular effects may further increase heart rate, blood pressure, or arrhythmia risk; pair-specific evidence varies.

CautionCaffeine

Concurrent exposure to agents with sympathomimetic cardiovascular effects may further increase heart rate, blood pressure, or arrhythmia risk; pair-specific evidence varies.

Legal status

US: prescription drugs — legal only through a clinician. GC-1 is not FDA-approved for human use. Products outside licensed dispensing are unapproved and quality-unverifiable.

Evidence base

Not auto-graded. This entry covers several different drugs, or a use the published research was never about, so no single letter honestly describes it. The reading below is real literature — read it against what this page says, not as a score.

Research (12)

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Where next

Every compound in the catalogThe full non-peptide index, with evidence grades.→The peptide indexInjectable peptides, half-lives and what trials used.→Spotting a scam vendorRed flags, COA checks and what traceability looks like.→