Testosterone replacement therapy (TRT)

TRT restores testosterone in men with documented hypogonadism (low serum testosterone plus symptoms), via gels, injections, or pellets. Benefits include improved libido, mood, lean mass, and bone density. Risks include erythrocytosis, fertility suppression, and cardiovascular effects; the recent TRAVERSE trial suggested cardiovascular non-inferiority but not benefit, though TRAVERSE also found increased rates of atrial fibrillation and venous thromboembolism in the testosterone arm. TRT is not validated as a longevity therapy in eugonadal men and remains controversial outside clinical hypogonadism.