Testosterone is essential not just for libido and muscle mass, but for energy, mood, bone density, and cardiovascular health. Low testosterone (also known as hypogonadism or androgen deficiency) is increasingly common in men due to aging, chronic stress, endocrine-disrupting chemicals, poor sleep, and underlying metabolic issues. Many cases are missed or misdiagnosed because of incomplete testing. Functional medicine addresses low testosterone by evaluating hormones holistically—including cortisol, thyroid, insulin, and nutrient cofactors—and restoring balance through lifestyle, targeted supplementation, and hormone replacement when appropriate.