T3, or triiodothyronine, is an active thyroid hormone that significantly affects the rate of metabolism. It is used medically for thyroid disorders, such as hypothyroidism. In bodybuilding, it is sometimes abused during cutting phases, which is associated with serious risks.

How T3 affects fat burning

increases basal metabolism

increases energy expenditure even at rest

accelerates lipolysis and mobilization of fat stores

can increase caloric expenditure even with the same food intake

affects the metabolism of carbohydrates and proteins

Risk of muscle loss

T3 not only increases fat loss, but if used incorrectly, it can also promote protein breakdown, increasing the risk of muscle loss.

Health risks

Use without medical indication can be dangerous:

heart palpitations and tachycardia

heart rhythm disorders

high blood pressure

muscle loss

nervousness and tremors

long-term disruption of the thyroid gland’s own function

Combinations in bodybuilding

In some bodybuilding circles, T3 is mentioned during the “cutting” phase with anabolic steroids, stimulants, growth hormone or clenbuterol. Such combinations significantly increase the risk of cardiovascular complications, nervous system overload and long-term hormonal consequences.

Summary