T2

A natural thyroid metabolite one step downstream of T3 in the hormone cascade. Your body makes it from the T3 and T4 your thyroid produces, though how much is genuinely uncertain: immunoassays give antibody-dependent values, and pilot mass spectrometry found serum concentrations below quantification in most samples. Until the 2000s nobody paid it much attention. Then rodent work showed T2 could boost mitochondrial fat oxidation and resting metabolic rate through pathways that overlap with T3’s but are not identical, acting partly through AMPK and SIRT1 rather than the classical thyroid receptor route.

That partial independence from the main thyroid axis is the pitch: a metabolic nudge without the full T3 ride of suppressed TSH, muscle wasting, and cardiac stress. The pitch held up in short rodent studies. In longer ones, the axis suppression came back. Whether T2 is genuinely sparing or just slower to suppress is the open question, and the human evidence is nowhere near answering it.

The human evidence is one report that barely qualifies as a study. The animal base is older and mixed.

The community runs T2 during cuts, usually alongside training and a calorie deficit, as a metabolic nudge rather than a standalone fat-loss agent. The logic: raise resting metabolic rate without the thyroid suppression and muscle cost of full-dose T3. Whether that logic holds past a few weeks is the open question from the rat data. Since T2 is sold as a supplement with no manufacturing oversight, source from a vendor with a COA. Keep runs short, get a thyroid panel before you start and after you finish, and do not stack T2 with liothyronine or levothyroxine unless you are monitoring closely with bloodwork.

The side profile looks mild in short use, but the thyroid axis is the thing to respect: