Long-acting testosterone undecanoate (TU) injection, but not oral TU, improves metabolic parameters This randomized, double-blind, double-dummy study was the first clinical trial to compare the efficacy and safety of long-term testosterone replacement therapy using two different preparations of testosterone undecanoate (TU), in hypogonadal men with metabolic syndrome (MetS) and/or type 2 diabetes mellitus (T2DM).1