Trans Erection: The Science of Erectile Function

Erectile function in transgender people follows the same core biology as in anyone else, but hormones, surgery, and individual goals can reshape how that biology plays out. The underlying mechanism relies on nitric oxide signaling in erectile tissue, and that tissue exists in both the penis and the clitoris because they develop from the same embryonic structure. What changes for trans individuals is the hormonal environment surrounding that tissue, the surgical modifications some people pursue, and the wide range of goals people bring to the table. Some trans women want to preserve erections; others welcome their decline. Some trans men seek penetrative capability through surgery; others are satisfied with growth from testosterone alone.

How Erections Actually Work

Whether the structure in question is a penis or a clitoris, the basic process is the same. Nitric oxide, released by nerve endings and the inner lining of blood vessels in erectile tissue, triggers a chain of chemical events that relaxes smooth muscle and allows blood to fill the spongy chambers of the organ. This was demonstrated directly in human tissue: when researchers stimulated corpus cavernosum samples with electrical fields, the tissue relaxed in a way that depended entirely on nitric oxide production, and blocking nitric oxide synthesis shut the response down.¹ That relaxation is what allows blood to rush in and create rigidity.²

Hormones modulate the system but are not the sole driver. Research on men with secondary hypogonadism (very low testosterone due to a pituitary issue) found that their spontaneous nighttime erections were substantially reduced, yet erections in response to visual sexual stimuli were relatively preserved.³ In other words, testosterone plays a strong role in spontaneous erections but less of a role in erections triggered by arousal. This distinction matters enormously for understanding what happens when trans people change their hormonal environment.

Shared Anatomy Between the Penis and Clitoris

The penis and the clitoris are homologous structures. During fetal development, they start as the same tissue and diverge under the influence of androgens. The neurovascular anatomy, meaning the way nerves and blood vessels are arranged, is similar in both.⁴ The clitoris contains erectile tissue whose pharmacology and microscopic structure parallel those of penile tissue.⁵ This homology is what makes testosterone-driven clitoral growth possible in trans men and why, mechanistically, the clitoris can become erect in the same way a penis does. It is also why surgical approaches that work with this tissue can produce sensation and, in some cases, erection-like responses.

What Feminizing Hormones Do to Erectile Function

Trans women on estrogen-based hormone therapy typically experience a decline in spontaneous erections over months to years. Testosterone levels drop, sometimes dramatically, and with them the hormonal support for nighttime and morning erections fades. Given what we know about testosterone’s role in spontaneous erections, this is predictable. The nitric oxide signaling pathway does not disappear, but with less androgenic stimulation, erectile tissue can atrophy over time if erections become infrequent. Some trans women welcome this as part of feminization. Others experience it as an unwanted side effect, particularly those who wish to use their genitals for penetrative sex or simply find erections important to their sexual experience.

The degree of erectile change depends heavily on the specific regimen. Estrogen combined with a strong antiandrogen like cyproterone acetate at high doses will suppress testosterone more aggressively than estrogen alone. For trans women or nonbinary individuals who want to feminize while preserving erectile function, clinicians sometimes prescribe estrogen-only regimens or combine estrogen with lower doses of antiandrogens or with 5-alpha reductase inhibitors instead.⁶ This can allow breast development and softer skin while keeping enough androgenic activity to maintain erections.

PDE5 inhibitors, the class of drugs that includes sildenafil and tadalafil, are sometimes used as adjuncts for trans women who want to maintain or recover erectile function while on feminizing therapy.⁷ These drugs work by inhibiting the enzyme that breaks down the signaling molecule responsible for keeping smooth muscle relaxed in erectile tissue. Because the nitric oxide pathway is still present, boosting it pharmacologically can restore functional erections even when testosterone is low. The evidence base for their use specifically in trans women is thin compared to their extensive track record in cisgender men, but the mechanism is the same.

Why Treatment Goals Vary So Widely

A community survey of people on feminizing hormone therapy revealed just how diverse expectations can be. About 16% of respondents considered increased sex drive a sign that their treatment was working, while 14% considered decreased sex drive a sign of efficacy.⁷ Those who view maintained libido and erectile function as important may benefit from less aggressive testosterone suppression and early conversations about medications that support erections. Those who want testosterone driven as low as possible may prefer stronger suppression even at the cost of erectile capacity.

This is an area where research on sexual quality of life before surgical intervention is revealing. In a study of gender-dysphoric adults awaiting genital surgery, over half rated their sexual life as poor or very poor. Being on hormonal treatment and having a partner were both associated with better sexual quality of life. The finding that hormonal treatment was linked to improvement suggests that even when erectile function changes, aligning the body with one’s gender identity can improve sexual satisfaction overall.

Testosterone and Erectile Growth in Trans Men

Trans men who start testosterone therapy typically experience significant clitoral growth, often noticeable within the first few months. A prospective study measuring clitoral dimensions at baseline and six months found that the clitoral index (a combined measure of size) more than doubled, jumping from roughly 94 mm² to about 224 mm². Blood flow through the dorsal clitoral artery also tripled.⁸ This growth is driven by the same androgenic mechanisms that cause penile development in puberty, and the result is tissue that can become erect in response to arousal. Many trans men refer to the enlarged clitoris as their penis or phallus, and for some, this growth provides enough functional capability that no surgical intervention feels necessary.

Research on men with low testosterone who received testosterone replacement also sheds light on what androgens do for erectile tissue over time. In one study, erectile function scores improved steadily over a year, and nighttime erections became both more frequent and longer-lasting after twelve months of therapy.⁹ While this study focused on cisgender men, the underlying biology applies: testosterone supports the vascular health and smooth-muscle responsiveness of erectile tissue regardless of the body it is in.

Metoidioplasty and Erectile Capability

Metoidioplasty is a surgical procedure that releases the testosterone-enlarged clitoris from its surrounding tissue to create a small phallus. Because the procedure works with the existing erectile tissue rather than constructing new tissue from a graft, the result has the potential for natural erections. In practice, though, erection quality varies. A survey of metoidioplasty patients found that 83% described their erections as either “larger but not hard” or “hard but not hard enough for penetration.” Only 6% reported erections hard enough for penetration, and 11% reported no enlargement at all.¹⁰

These numbers represent a significant limitation for people whose primary goal is penetrative intercourse. The small size of the neophallus after metoidioplasty, usually a few centimeters in length, also constrains what is mechanically feasible. However, many patients pursue metoidioplasty for goals other than penetration: standing urination, genital appearance that aligns with their identity, and the ability to experience erection and sensation in a penis-like structure. PDE5 inhibitors and intracavernosal injections are being explored as ways to improve erectile rigidity after metoidioplasty, though evidence for their effectiveness in this population is still early.

Phalloplasty and the Challenge of Building Erections From Scratch

Phalloplasty constructs a full-sized penis using tissue grafted from another part of the body, most commonly the forearm (radial forearm free flap) or the thigh. Unlike metoidioplasty, the resulting structure has no intrinsic erectile tissue. The grafted skin, fat, and muscle cannot engorge with blood the way native erectile tissue does. To achieve penetrative rigidity, trans men who have phalloplasty typically need a penile prosthesis implanted at a later stage.

This is where things get surgically complex. In a cisgender man receiving a penile implant, the device sits inside the corpora cavernosa, the natural paired cylinders of erectile tissue that run the length of the penis. A neophallus does not have corpora cavernosa, so the prosthesis must be anchored differently, usually to the pubic bone.¹¹ The blood supply in a neophallus is also more fragile than in native tissue, which raises the risks of erosion, extrusion, and infection.¹²

A meta-analysis of penile prosthesis outcomes in trans men found overall complication rates of about 38% for inflatable devices and 37% for malleable (semi-rigid) ones. The most common problems with inflatable prostheses were infection (about 15%) and device dysfunction (about 13%). Malleable devices had similar overall rates but a different complication profile, with dislocation being the most frequent issue (about 15%). Explantation, meaning the device had to be removed entirely, was needed in roughly one in five cases for inflatable devices and about one in eight for malleable ones.¹³ These rates are notably higher than in cisgender men, largely because of the anatomical differences described above.

Despite the complication rates, satisfaction remains high. A systematic review found that roughly half to over 90% of patients were satisfied with their prosthesis, and 77% to 100% were engaging in sexual intercourse.¹² This gap between complication rates and satisfaction suggests that for many trans men, the functional gains from a prosthesis outweigh the risks and the likelihood of revision surgery. Some flap choices in phalloplasty, like the free fibula flap, incorporate a piece of bone that provides built-in rigidity without a prosthesis, though this approach has its own drawbacks including a risk of erosion over time.¹⁴

Sensation in a Constructed Phallus

Erectile rigidity is only part of the picture. Sensation determines whether an erection translates into sexual pleasure, and sensation after phalloplasty is complicated. In a study measuring both objective and experienced sensitivity, 92% of participants reported at least some tactile sensation in their neophallus, and about 89% experienced erogenous sensation. However, objective tactile sensitivity was significantly reduced compared to the skin at the donor site, and the tip of the neophallus was less sensitive than the base.¹⁵

One encouraging finding was that sensitivity improved with time. Nerve regrowth is a slow process, and the study found that longer follow-up was associated with better sensation. In many phalloplasty techniques, the native clitoris or its nerve bundle is buried at the base of the neophallus, providing a concentrated zone of erogenous sensitivity even when the rest of the structure has limited feeling. This is why some trans men describe a split experience: the base of the penis is where pleasure concentrates, while the shaft provides pressure and position awareness rather than fine-grained sensation.

How Hormones Reshape Orgasm Itself

Beyond erection mechanics, gender-affirming hormone therapy changes the subjective experience of orgasm in ways that surprise many people. A long-term follow-up study found that trans women on estrogen reported needing more time to reach orgasm, but also reported longer orgasm duration and greater overall satisfaction with orgasm quality. Over half reported experiencing orgasms in body locations they had not experienced them before.¹⁶ Trans men on testosterone similarly reported longer orgasm duration and greater satisfaction.

A pilot study quantified some of these shifts. Trans women’s average time to orgasm nearly doubled, from about 8 minutes to about 14 minutes. Their reported orgasm duration increased from about 9 seconds to roughly 34 seconds. Before hormones, 83% of trans women described their orgasms as a short, single-peak event. Afterward, 74% described longer, multiple-peak orgasms instead. Trans men experienced a significant increase in orgasm duration as well, from about 15 seconds to about 26 seconds.¹⁷ These changes likely reflect both the direct effects of altered sex hormones on nerve sensitivity and the psychological effects of living in a body that feels more congruent.

Vascular Health and Long-Term Erectile Viability

Because erections depend on healthy blood vessels, anything that affects cardiovascular health affects erectile function. Trans women on estrogen therapy carry some additional cardiovascular considerations, though the exact magnitude of risk remains debated. The research is mostly observational, and disentangling the effects of hormones from confounding factors like smoking, alcohol use, HIV status, and preexisting conditions has proven difficult.¹⁸ Estrogen may slightly increase the risk of blood clots, particularly oral forms, but newer transdermal formulations appear to carry a lower risk.

For trans men, testosterone therapy can shift cholesterol profiles in a less favorable direction and may raise blood pressure modestly, both of which affect vascular health over decades. The practical takeaway is that maintaining cardiovascular health through exercise, not smoking, and managing blood pressure is just as important for long-term erectile function in trans people as it is for anyone else. A person who preserves erectile tissue through careful hormonal management but develops atherosclerosis may still lose function through the same pathway as a cisgender man with cardiovascular disease.

Bioengineered Erectile Tissue on the Horizon

The most ambitious frontier in this area is tissue engineering. Researchers have managed to construct functional erectile tissue from scratch in animal models. In a widely cited rabbit study, bioengineered corpora cavernosa were created using collagen scaffolds seeded with the animal’s own cells. The resulting tissue demonstrated structural and functional characteristics similar to native erectile tissue, and male rabbits who received bilateral implants were able to mate and impregnate females.¹⁹

More recent work has focused on reconstructing both the spongy inner tissue and the tough outer casing of erectile bodies. Studies using tissue-engineered, cell-seeded scaffolds have shown that the grafts integrate without immune rejection and improve both pressure measurements inside the erectile chambers and the expression of nitric oxide, the key molecule for erection.²⁰ The gap between a successful rabbit experiment and a viable human therapy remains enormous. But if bioengineered erectile tissue eventually reaches the clinic, it could eliminate the need for mechanical prostheses after phalloplasty, offering trans men a neophallus that achieves and loses erections the way native tissue does. For now, that remains a research goal rather than a clinical option.