The purpose of this study is to evaluate the effects on serum testosterone (ST) after 6 weeks of subcutaneous (SC) administration of different doses and dosing frequencies of TAK-448 to middle-aged and older men with low ST levels.

The drug tested in this study is called TAK-448. TAK-448 was tested to define a dose and dose frequency which results in a clinically relevant improvement in ST in middle-aged and older men with low ST levels. This study looked at ST levels in men who took TAK-448. The study enrolled 17 participants. Participants were randomly assigned (by chance, like flipping a coin) to one of the following treatment groups-which remained undisclosed to the participants and study doctor during the study (unless there is an urgent medical need): * TAK-448 0.1 µg * TAK-448 0.3 µg * TAK-448 1.0 µg * Placebo (dummy inactive injection) - this was a injection that looks like the study drug but has no active ingredient All participants received subcutaneous injection either once daily on Days 1 through 42, or twice weekly on Days 1 through 39 or once weekly on Days 1 through 36. This single-center trial was conducted in the United States. The overall time to participate in this study is up to 56 days. Participants made daily visits to the clinic for 8 weeks, and were contacted by telephone 14 days after last dose of study drug for a follow-up assessment.