People with depression often have low levels of testosterone. Researchers from West Virginia University reviewed seven studies into the use of testosterone for depression which covered a total of 364 people. They found that testosterone significantly improved people's depression symptoms, particularly if they suffered from low testosterone or HIV/AIDS. Testosterone gel was found to be more effective than intramuscular injection.
Zarrouf, Fahd Aziz ... [et al] - Testosterone and depression: systematic review and meta-analysis Journal of Psychiatric Practice July 2009, 15(4), 289-305