In a trans woman on feminizing hormone therapy (estradiol plus an anti‑androgen such as spironolactone, cyproterone acetate, a GnRH agonist, or a 5‑α‑reductase inhibitor), does penile shrinkage occur and is it permanent?

Penile Shrinkage with Feminizing Hormone Therapy

Yes, penile shrinkage does occur with feminizing hormone therapy, and it is likely permanent if therapy continues long-term. 1

Mechanism and Expected Changes

Feminizing hormone therapy induces decreased testicular size and reduced erectile function through testosterone suppression and estradiol effects. 1 The physical changes result from:

• Testosterone suppression to <50 ng/dL (female range) combined with estradiol therapy, which directly affects genital tissue. 2, 3
• Decreased erectile function and libido are expected effects that contribute to tissue changes. 1
• Testicular atrophy occurs as a documented effect of anti-androgen therapy. 1

While guidelines explicitly document decreased testicular size and reduced erectile function, they do not specifically quantify penile length changes in transgender women. 1 However, the physiological mechanisms are well-established.

Evidence from Androgen Suppression Studies

The most relevant data comes from prostate cancer patients receiving androgen suppression therapy (similar hormonal mechanisms):

• Significant penile shortening occurred in men receiving luteinizing hormone-releasing hormone agonists (the same GnRH agonists used in transgender care), with mean stretched penile length decreasing from 14.2 cm to 8.6 cm at 18 months (p <0.001). 4
• This represents approximately 40% reduction in length with androgen suppression alone. 4

Permanence of Changes

The changes are likely permanent while on therapy and potentially irreversible:

• Physical characteristics induced by hormonal therapy that involve tissue structure changes (like voice deepening in masculinizing therapy) tend to be irreversible even after stopping hormones. 1
• Unlike reversible effects such as muscle mass or fat distribution, genital tissue changes from prolonged androgen suppression appear to be structural. 4
• If hormone therapy is discontinued for ≥3 months, some physiological parameters return to baseline, but structural tissue changes may not fully reverse. 5

Clinical Implications and Counseling

Patients must be counseled before starting therapy that genital changes, including potential penile shrinkage, may occur. 4 This is particularly important for:

• Transgender women considering future genital gender-affirming surgery (vaginoplasty), where penile tissue is used for surgical construction. 1
• Individuals who may want to preserve erectile function or genital size.
• Those considering fertility preservation, which should be discussed before initiating therapy. 2, 3

Common Pitfalls to Avoid

• Failing to provide comprehensive counseling about all genital changes before starting feminizing hormone therapy. 2, 3
• Not discussing surgical implications if the patient may want vaginoplasty in the future, as tissue availability affects surgical outcomes. 1
• Assuming all changes are reversible if therapy is stopped—structural tissue changes may be permanent. 1, 5

Monitoring Considerations

While penile size is not routinely measured in transgender care protocols, patients should be informed that:

• Reduced erectile function typically begins within the first few months of therapy. 1
• Testicular atrophy is expected and documented as a standard effect. 1
• Changes progress over 12-36 months as hormone levels stabilize in the female range. 1