T3 / T4 Thyroid (Liothyronine / Levothyroxine)
Evidence: ★★★★☆ · Status: Prescription
In plain English
The metabolic "master gain" hormone. Legitimate for underactive thyroid; taken by physique athletes to burn faster — but it burns muscle too and suppresses your own thyroid.
How it works
Thyroid hormones bind nuclear thyroid receptors (THRA/THRB), raising basal metabolic rate and thermogenesis genome-wide. Misused by bodybuilders to accelerate fat loss.
Molecular target & official sources
THRB thyroid hormone receptor beta (NCBI Gene) · Liothyronine (PubChem CID 5920)
Watch out
Muscle loss, cardiac strain, thyroid suppression. **Bottom line:** Treat deficiency; risky as a cutting tool.
Helps with: Build Muscle & Strength · Lose Fat · Hormones & Testosterone
Stacks with
Shares a pathway — often paired with: Omega-3 (EPA/DHA), Vitamin D3 (+ K2), Testosterone (TRT), Finasteride / Dutasteride.
Availability & where to buy
Prescription only. Prescription-only — a doctor must prescribe it. Not sold over the counter. (In Singapore: HSA-regulated.)
How it works: the Nuclear receptors pathway →
Used in these protocols
Common questions
Does T3 / T4 Thyroid (Liothyronine / Levothyroxine) actually work?
Human-evidence rating: 4 of 5. The metabolic "master gain" hormone. Legitimate for underactive thyroid; taken by physique athletes to burn faster — but it burns muscle too and suppresses your own thyroid.
What are the risks or side effects of T3 / T4 Thyroid (Liothyronine / Levothyroxine)?
Muscle loss, cardiac strain, thyroid suppression. Bottom line: Treat deficiency; risky as a cutting tool.
Is T3 / T4 Thyroid (Liothyronine / Levothyroxine) legal or approved?
Regulatory status: Prescription.