How is the T3 hormone used in bodybuilding to lose weight?

Triiodothyronine (T3) is a thyroid hormone involved in regulating metabolism and fat burning. Because of this, there is a growing interest in knowing how to use T3 to lose weight, especially among bodybuilders whose primary goal is to change their body.

In this text, we will see what T3 is for, how it works (in practice), its positive effects and, most importantly and ignored: the side effects associated with its use.

The hormone T3, or triiodothyronine, is a hormone produced by the thyroid and plays a central role in regulating metabolism.

In simple terms, the hormone alters metabolism by acting within cells, stimulating the production of proteins that increase mitochondrial activity — where calories are burned.

When there is more T3 than normal in the body, energy and heat production increases, causing the body to burn more calories, even at rest and without making changes to diet.

The presence of T3 in cells also reinforces the action of other hormones that help burn fat, such as adrenaline, which, among its many functions, can facilitate the breakdown of fat to be used as energy.

You don't need to delve too deeply into the subject to understand why many people look to T3 as a way to accelerate fat burning, especially in the context of bodybuilding and weight training.

However, it is important to emphasize that T3 is a hormone naturally produced by the body and, as such, requires a balance, where having less or more than necessary will have adverse effects on health, both in the short and long term.

We all produce enough T3 to maintain a healthy metabolism. Therefore, to obtain the benefits of the hormone for weight loss, it is necessary to increase your levels above the natural level.

This can only be done by adding (supplementing) extra T3 hormone in its synthetic form, something that is done through the use of liothyronine sodium, which is a “copy” of the hormone in oral tablet form.

By increasing T3 levels, the effects usually appear quickly, within a matter of days or a few weeks, as it acts directly on the metabolism and the response is usually rapid.

Despite this, and even if its effects occur at rest (without doing physical activity) and without changes in diet, the best results can only be obtained in combination with physical activity and changes in eating habits.

The use of T3 in the context of body change should be seen more as an “accelerator” of results and less as the main cause.

The most common use of T3 for fat burning tends to be in the form of pyramid-type cycles, starting with lower doses — between 12.5 and 25 mcg per day — and progressively increasing every one to two weeks, reaching 75 or even 100 mcg per day (1).

As genuine T3 is not easily obtained, many products available on the market are of dubious origin and there may be significant variation in potency, which leads many to use doses much higher than those mentioned, which involves considerable risks.

Regarding the time of use, a common cycle does not usually last more than 6 weeks (2), with interruption done gradually, reducing the dosage weekly to allow the body to adapt.

This is because T3 suppresses the body's natural production of the hormone, something that can take weeks to return to normal levels after the end of the cycle.