Normal Testosterone levels contribute to a healthier libido, prostate health, fertility, and better sexual function – and satisfaction. Normal testosterone levels also encourage muscle development and contribute to weight loss. It is also known to help maintain energy levels, contribute to better sleep, stabilize mood, and promote a greater ability to deal with stress. All of which are known to decline with age and the onset of andropause. Simply stated, a man needs normal testosterone levels to stay fit and feel energized. Tribulus terrestris supports normal testosterone levels.