Administration of a transdermal testosterone (T) gel formulation to hypogonadal men provided dose-proportional increases in serum T levels to the normal adult male range. Testosterone 1% gel (50 or 100 mg/day) was compared to the permeation-enhanced T patch. After 180 days, skin irritation was reported in 5.5% of subjects treated with T gel and in 66% of subjects in the permeation-enhanced T patch group. This research at UCLA concluded that T gel replacement improved sexual function and mood, increased lean mass and muscle strength (principally in the legs), and decreased fat mass in hypogonadal men with less skin irritation and discontinuation compared with the recommended dose of the permeation-enhanced T patch.
The following study concluded that replacing testosterone in hypogonadal men increases bone mineral density of the spine and hip, fat-free mass, prostate volume, erythropoiesis, energy, and sexual function. The full effect of testosterone on bone mineral density took 24 months, but the full effects on the other tissues took only 3-6 months.