T4 – Thyroxin

T4 (levothyroxine, also called thyroxine) is a synthetic version of the hormone the thyroid gland naturally produces. On its own it is largely inactive, but the body converts a portion of it into T3, the hormone that actually drives metabolic rate. That conversion is why users take T4 to nudge energy expenditure up during a cutting phase rather than expecting an immediate effect.

As a guide and not medical advice, this compound is commonly reported to be started at a low dose such as half a 100mcg tablet in the morning on an empty stomach, with any increase only considered after bloodwork confirms low T4 levels. Runs are usually kept short, in the region of six to eight weeks, since thyroid hormones affect the whole endocrine system and are not meant to be used indefinitely.

Pushing thyroid hormone above what the body needs can bring on a racing heart, palpitations, anxiety, sweating, heat intolerance, tremor and unwanted weight loss, since these are the classic signs of overactive thyroid function. Baseline and repeat bloodwork covering TSH, free T4 and free T3 is the standard way users keep an eye on this, alongside regular checks on resting heart rate and blood pressure.

T3 is the active hormone and works faster and more directly, while T4 has to be converted by the body first, which gives a slower, more gradual rise in metabolic effect. Some users find T4 easier to control for that reason, since sudden spikes in thyroid activity are less likely, though both still require careful monitoring rather than casual dosing.

T4 is a thyroid hormone rather than an anabolic steroid, so it does not suppress natural testosterone production and a dedicated PCT is not required on its own. If it is being run alongside actual anabolic compounds, PCT needs should be based on those compounds rather than the T4 itself.

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