Testosterone Does Not Increase Penis Size in Healthy Adult Males
No, testosterone replacement therapy (TRT) will not increase penis size in a healthy adult male with normal testosterone levels. Penis growth in response to testosterone occurs only during specific developmental windows—primarily in utero and during infancy/early childhood—and this capacity is lost after puberty 1, 2.
Critical Developmental Window
Penile growth from testosterone is limited to prepubertal males with pathologic testosterone deficiency (micropenis due to hypogonadotropic hypogonadism), where treatment before age 2 or during childhood can normalize penile length to within 2 standard deviations of the mean adult size of 12.4 ± 2.7 cm 2.
After puberty, the penis loses its androgen-responsive growth capacity entirely—even in men who had micropenis and received testosterone treatment in childhood, no additional penile growth occurred during adolescence or adulthood despite achieving normal testosterone levels 1, 2.
In the only long-term follow-up study of micropenis patients treated with testosterone, those who received topical testosterone in childhood (N=5) had identical adult penile size compared to untreated controls (N=3), demonstrating that even in severely testosterone-deficient individuals, adult penile tissue does not respond to androgens 1.
What TRT Actually Does in Adults
The American College of Physicians guidelines establish that TRT in adult men with age-related low testosterone provides 3:
- Small improvement in sexual function (erectile function, libido, overall sexual satisfaction) with a standardized mean difference of 0.35 for global sexual function and 0.27 for erectile function specifically
- Small improvement in quality of life (SMD 0.33), though this may be driven primarily by the sexual function improvements
- Little to no effect on physical function, energy, vitality, or cognition—improvements in these domains were less than clinically meaningful (SMD <0.2)
Common Pitfall to Avoid
Do not confuse erectile function improvement with anatomic penile growth. TRT may improve erections in hypogonadal men by acting as a vasodilator of penile arterioles and cavernous sinusoids 4, but this hemodynamic effect does not translate to structural tissue growth or increased penile dimensions 1, 2.
The Bottom Line for Clinical Practice
In healthy adults with normal testosterone: TRT provides no benefit whatsoever and carries unnecessary risks (cardiovascular events, erythrocytosis, suppression of spermatogenesis) 3.
In adults with confirmed hypogonadism and sexual dysfunction: TRT may modestly improve erectile function and libido, but will not increase penile size 3, 4.
Only in prepubertal boys with pathologic micropenis: Testosterone treatment can normalize penile growth, but this indication is irrelevant to the adult population 2, 5.
The American College of Physicians recommends discontinuing TRT if there is no improvement in sexual function after 12 months, as this is the only evidence-based indication for therapy in men with low testosterone 3, 6.