Can FT4 help with Sport?

The question of whether FT4 (free thyroxine) can aid sport performance has weak scientific support. FT4 is a thyroid hormone that regulates basal metabolic rate and muscle protein turnover. While maintaining normal FT4 levels is essential for health, deliberately raising FT4 through supplementation or medication to enhance athletic performance is not backed by robust evidence. Overuse can induce hyperthyroidism, leading to tachycardia, muscle wasting, and cardiac strain. In athletes with normal thyroid function, no proven ergogenic benefit exists. Evidence is based on mechanistic reasoning and case reports, not RCTs. Caveat: FT4 is a prescription drug; self-administration without medical indication is dangerous. Conclusion: FT4 is not a sport supplement; balance is key.