A measured look at liothyronine (T3), why it is used for fat loss, and the muscle and cardiac risks that come with suppressing your own thyroid.
At a glance
Liothyronine is synthetic triiodothyronine (T3), the active thyroid hormone. Medically it treats hypothyroidism and certain other thyroid conditions. Non-medically it is used to accelerate fat loss, usually during a contest prep or aggressive cut, because raising circulating T3 raises metabolic rate directly. The catch is that exogenous T3 suppresses your own thyroid output, and used carelessly it burns muscle alongside fat.
This is an educational tracking guide, not a recommendation. T3 is a real hormone with real feedback loops, and misuse has real consequences.
Doses are reported in micrograms and are commonly titrated up from a low starting point and then tapered down at the end rather than stopped abruptly, to give the suppressed thyroid time to recover. Many users pair it with adequate protein and resistance training specifically to blunt muscle loss. These are patterns described in the literature, not a dose recommendation.
T3 speeds fat loss only on top of a diet that already works. What it does not do is spare muscle on its own - if anything it accelerates loss of lean tissue when calories and protein are low. Strength often dips. The tapered exit matters as much as the run.
Exogenous T3 suppresses your natural thyroid function, can strain the heart, and can drive muscle loss when misused. Excess thyroid hormone can cause arrhythmia, and long or high-dose use risks bone loss and lasting axis disruption. It is prescription-only for good reasons, and anyone using it should have real thyroid bloodwork and ideally medical oversight rather than guessing.
Peptid AI is an educational and self-tracking tool. Nothing in this post is medical advice. Doses mentioned reflect what is commonly reported in research literature — they are not recommendations. Always consult a qualified physician before starting, changing, or stopping any protocol.