Does low testosterone affect erection or libido?

Low Testosterone Affects Both Libido and Erection, But the Impact Differs

Low testosterone primarily and consistently impairs libido (sexual desire), while its effect on erectile function itself is less direct and more variable—testosterone is essential for libido, but erections can often occur with low testosterone levels, though erectile quality may be compromised. 1, 2

Testosterone's Differential Effects on Sexual Function

Impact on Libido (Sexual Desire)

• Testosterone is a key central modulator of sexual desire, and diminished libido is one of the hallmark symptoms of hypogonadism 1, 2
• In complete hypogonadism, libido becomes very low, and testosterone replacement therapy consistently restores sexual desire 3
• The American College of Physicians recognizes decreased libido as a primary symptom of hormonal dysfunction that warrants testosterone measurement 1
• Testosterone replacement therapy produces small but significant improvements in sexual desire and libido (standardized mean difference 0.35) in men with confirmed hypogonadism 2, 4

Impact on Erectile Function

• The relationship between testosterone and erectile function is more complex and less consistent than its effect on libido 5
• Animal studies demonstrate that testosterone acts as a vasodilator of penile arterioles and cavernous sinusoids, suggesting direct effects on erectile tissue 6, 5
• However, in humans, circulating testosterone levels well below the normal range are necessary for normal erections, but higher levels within the normal range may not have major impact on erectile function 5
• Following castration, most but not all men experience partial or complete loss of erection, indicating testosterone is important but not absolutely required for all erectile function 5

Clinical Evidence on Testosterone's Role

Prevalence of Hypogonadism in ED

• Hypogonadism occurs in approximately 5-20% of men presenting with erectile dysfunction, making it a relatively uncommon but important cause 6, 5
• Among men seeking consultation for sexual dysfunction, approximately 36% have hypogonadism 1
• There is generally a lack of association between serum testosterone levels, when present in normal or moderately low levels, and erectile function 5

Treatment Response Patterns

• Testosterone replacement therapy improves sexual activity and sexual desire, but not erectile function directly in the most recent high-quality trial (TRAVERSE Sexual Function Study, 2024) 4
• In this 2-year randomized trial of 1,161 hypogonadal men with low libido, testosterone gel improved sexual activity by 0.47-0.49 acts per day and improved hypogonadal symptoms and sexual desire, but did not improve erectile function compared to placebo 4
• Erectile function is more likely to improve with testosterone therapy in patients with severe degrees of hypogonadism rather than mild to moderate deficiency 5
• One study found that normalization of testosterone levels was associated with only short-term improvement in erectile function (at 1 month), with declining satisfaction scores from 1 to 6 months 7

Mechanism and Clinical Implications

Why Testosterone Affects Libido More Than Erections

• Testosterone primarily acts centrally (in the brain) to modulate sexual desire, which is why libido is consistently affected by low testosterone 1, 3
• The peripheral effects on erectile tissue are present but less clinically significant in most cases, as the phosphodiesterase 5 (PDE5) pathway and nitric oxide mechanisms can function relatively independently of testosterone 6
• A minimal level of testosterone is required for complete effect of PDE5 inhibitor therapy, explaining why some men fail sildenafil or other ED medications when testosterone is low 1

Combination Therapy Considerations

• Hypogonadism is a potential cause of lack of response to PDE5 inhibitor therapy, and testosterone replacement improves response 1
• Recent data support the success of combination therapy with sildenafil and testosterone in men with both conditions 6
• The Princeton III Consensus recommends measuring testosterone levels in all men with organic ED, especially those for whom PDE5 inhibitor therapy failed 1

Diagnostic Approach

When to Suspect Testosterone Deficiency

• Consider testosterone measurement in men presenting with decreased libido and decreased spontaneous erections as primary symptoms 1
• Physical findings suggesting hypogonadism include testicular or muscle atrophy 1
• Morning total testosterone should be measured on two separate occasions, with levels below 300 ng/dL indicating potential hypogonadism 2
• Free or bioavailable testosterone should be measured in conditions that alter sex-hormone-binding globulin levels, such as in elderly men and obesity 5

Critical Clinical Caveat

The effect of testosterone replacement therapy on sexual function is more obvious when testosterone is severely low and there are no other causes of impaired sexual desire or erectile dysfunction 3. In aging men, multiple factors beyond testosterone (health status, relationship issues, socioeconomic and psychological factors, and coexisting erectile dysfunction) must be considered, as these can decrease both sexual desire and testosterone levels independently 3.