Why they look alike
Testosterone influences mood, motivation, and energy, so a deficiency can produce symptoms that look a great deal like depression. The reverse is also true — depression can blunt libido and drain energy. The symptom lists overlap enough that one is regularly mistaken for the other.
Where they differ
Depression typically carries features that low testosterone alone usually doesn't — persistent hopelessness, loss of interest in things that normally bring joy, and changes in thinking patterns. Low T more often presents as physical flatness: fatigue, weaker erections, lost strength, with mood as one piece rather than the center.
They can coexist
This isn't always either/or. Low testosterone can contribute to depressed mood, and treating it sometimes lifts symptoms — but TRT is not a treatment for clinical depression, and assuming it is can delay proper mental-health care.
The right approach
A blood test settles the hormonal question quickly. If testosterone is low and symptoms fit, treating it may help. If mood symptoms persist or are severe, they deserve mental-health support in their own right. A good physician looks at the whole picture rather than forcing one explanation.