What Is the Xiaflex Success Rate for Peyronie’s Disease?

Men treated with Xiaflex (collagenase clostridium histolyticum, or CCH) for Peyronie’s disease see an average curvature reduction of about 34%, or roughly 17 degrees, based on the pivotal clinical trials that led to FDA approval. That number, though, is an average across hundreds of men, and it hides a wide range of individual outcomes. Some men respond dramatically, while others see little change. What determines where you fall depends on several factors, from how curved you are at baseline to whether your plaque has calcified, and the growing body of real-world data tells a more nuanced story than the headline figure suggests.

What the Pivotal Trials Found

The cornerstone evidence for Xiaflex comes from the IMPRESS trials, two large, double-blinded, placebo-controlled studies involving over 800 men. Participants received up to four treatment cycles spaced six weeks apart, with two injections of 0.58 mg per cycle followed by a manual “modeling” session in which the penis is stretched to help break down the plaque. Men in the treatment group achieved an average 34% reduction in penile curvature, translating to a mean improvement of about 17 degrees. The placebo group, by comparison, saw about an 18% reduction, or roughly 9 degrees. The difference was statistically meaningful and formed the basis for the drug’s FDA approval.¹

Separate multi-institutional analyses confirmed these results held up outside the controlled trial setting. Real-world use following the same injection protocol produced meaningful curvature improvements with a low complication rate.² Still, it is worth understanding what “meaningful improvement” actually looks like in practice, because the raw numbers do not always tell the full story.

What “Success” Actually Means

A persistent source of confusion around Xiaflex is what counts as a successful outcome. In the IMPRESS trials, success was measured primarily as degree improvement in curvature. But a 17-degree average improvement means very different things depending on where you start. If your curvature is 50 degrees, coming down to 33 degrees may make intercourse considerably easier. If you start at 30 degrees, dropping to 13 degrees might feel like a near-complete correction. The same average improvement maps onto widely different functional experiences.

A cost-effectiveness analysis that modeled Xiaflex against surgery and penile traction therapy estimated overall success rates of 66% for CCH, compared with 96% for surgery and 48% for traction alone.³ That 66% figure is useful as a rough benchmark, but it comes from modeled data rather than a direct head-to-head trial, and the definition of success baked into the model shapes the number. In real-world practice, some men who technically fall short of a clinical “response” threshold still report improved sexual function and reduced bother. Others who achieve a measurable improvement in degrees may still feel dissatisfied if they expected a complete straightening.

Who Gets the Best Results

Not everyone responds equally to Xiaflex, and researchers have spent significant effort trying to identify which patients are most likely to benefit. The single most consistent predictor is baseline curvature: men who start with more severe curves tend to see bigger absolute improvements. One study found that for every 10-degree increase in starting curvature, the odds of meaningful improvement rose by about a third.⁴ After accounting for baseline curvature, no other single variable in that analysis independently predicted improvement.

A larger prospective series, however, identified additional factors that mattered on multivariate analysis. Men with hourglass or indentation deformities tended to see greater improvement, as did men who reported strong nocturnal erections and higher frequency of intercourse. Men with pure lateral (side-to-side) curvatures fared worse than those with dorsal or complex curves. The study also found that men who experienced a “popping” sensation or hematoma during treatment, signs that plaque disruption was occurring, tended to have better curvature outcomes.⁵

A literature review looking across multiple studies identified four characteristics tied to a favorable response: baseline curvature in the 30-to-60-degree range, longer disease duration, mild to moderate baseline erectile function, and low calcification within the plaque.⁶ The finding about disease duration is somewhat counterintuitive: you might expect that treating earlier would be better, but established, stable plaque may actually be more amenable to enzymatic breakdown than actively inflamed tissue.

When Xiaflex Is Less Likely to Work

Calcification within the Peyronie’s plaque is the factor that most consistently limits Xiaflex’s effectiveness. Xiaflex works by degrading collagen fibers in the plaque; once those fibers have mineralized into calcium deposits, the enzyme simply cannot break them down effectively. A review of intralesional therapies noted that while some patients with calcified plaques may still benefit, the overall evidence does not strongly support using CCH in these cases.⁷ The literature review mentioned above flagged calcification as potentially the most significant limiting factor, precisely because it represents a fundamental mismatch between what the drug does and what the plaque has become.⁶

This is one reason many urologists recommend imaging before starting treatment. An ultrasound or X-ray can reveal the extent of calcification, and heavy calcification may steer the conversation toward surgery rather than injections. Men with minimal or no calcification and a curvature in the moderate range are the best candidates, and providers familiar with these predictors can set more realistic expectations before treatment begins.

Fewer Injections May Work Just as Well

The standard IMPRESS protocol calls for up to eight injections across four cycles. That is a lot of office visits, expense, and discomfort. Researchers have explored shortened protocols, and the early findings are encouraging. One study evaluated a modified approach using just three injections and found a 31.4% reduction in curvature, comparable to the roughly 34% seen in the full eight-injection trials.¹ The authors of that modified protocol concluded the approach was safe, effective, and more cost-efficient, with the added benefit of potentially improving patient compliance by reducing the treatment burden.⁸

This matters for real-world success rates because a substantial number of men do not finish the full protocol. In one high-volume practice, about a third of patients who started Xiaflex did not complete all eight injections. The reasons varied: roughly 27% stopped because they were satisfied with their improvement, 21% stopped because they were not seeing enough improvement, 15% had bothersome side effects, and 12% opted for surgery instead. Other reasons included cost, pandemic-related pauses, and transferring care.⁹ A protocol that achieves similar results with fewer injections could meaningfully increase the proportion of men who finish treatment and reduce costs at the same time.

Adding Traction Therapy to Xiaflex

One of the more promising developments in Peyronie’s treatment is combining Xiaflex injections with penile traction therapy. The idea is straightforward: the enzyme weakens the plaque, and mechanical stretching helps remodel the tissue while it is healing. Preliminary data on combining Xiaflex with a traction device called RestoreX showed greater improvements in both curvature and penile length compared with Xiaflex alone.¹⁰

The large prospective study on outcome predictors reinforced this finding: on multivariate analysis, RestoreX use was independently associated with better curvature outcomes. Of all the factors the researchers assessed, traction device use was linked to the largest degree of additional improvement.⁵ The combination approach has not yet been tested in a large randomized controlled trial, so the evidence is still building. But for men already choosing Xiaflex, adding a traction regimen appears to improve the odds of a good result and may help address the perceived length loss that many men report after any Peyronie’s treatment.

Safety and Side Effects

Xiaflex’s side-effect profile is mostly local and manageable. The most common reactions are bruising, swelling, and pain at the injection site, sometimes extending along the shaft. In a large open-label study, most adverse events were mild or moderate in severity. Serious treatment-related events were rare: the study reported two cases of penile hematoma requiring treatment and one corporal rupture, all of which resolved.¹¹

Corporal rupture is the event that understandably worries patients the most. It involves a tear in the tunica albuginea, the tough tissue surrounding the erectile chambers, and typically requires surgical repair. While frightening, it is uncommon. The drug’s prescribing information includes a boxed warning about the risk, and patients are instructed to avoid sexual activity for at least two weeks after each injection cycle to minimize the chance of rupture. Following post-injection activity restrictions is not optional; it is a genuine safety measure.

The fact that men who experienced a hematoma or popping sensation during treatment tended to have better curvature outcomes highlights an uncomfortable paradox: some of the most alarming-sounding events during treatment are actually signs that the plaque is being disrupted, which is the entire point.⁵ Providers experienced with the procedure can help patients distinguish between expected treatment effects and warning signs that need medical attention.

How Xiaflex Stacks Up Against Surgery on Cost

Surgery remains the most reliable way to correct Peyronie’s curvature, with modeled success rates around 96%. But it comes with trade-offs: potential length loss, changes in sensation, and the risks of any surgical procedure under anesthesia. Conference data comparing long-term satisfaction between Xiaflex and surgery have suggested that men treated with Xiaflex reported higher satisfaction at three years and lower rates of perceived length loss, current pain, and sensation changes. These findings challenge the long-standing assumption that surgery should always be the first-line definitive treatment.

From a pure cost perspective, Xiaflex is the most expensive option per patient. A cost-effectiveness model estimated mean per-patient costs at about $33,600 for CCH, compared with roughly $11,400 for surgery and under $900 for traction therapy alone over a ten-year horizon.³ Both surgery and Xiaflex produced quality-of-life gains over traction alone, but neither cleared the conventional cost-effectiveness threshold of $100,000 per quality-adjusted life year compared with traction, making traction the most cost-effective strategy in the model.

For many men, though, the decision between Xiaflex and surgery is not purely about cost. It is about tolerance for surgery, recovery time, the desire to avoid general anesthesia, and how much curvature correction is needed. Men with curvatures above 60 or 70 degrees, or those with severe erectile dysfunction that may need a penile implant, are often better served by surgery. Men with moderate curvature who want a nonsurgical option and can absorb the cost or have insurance coverage may reasonably choose Xiaflex.

How the Drug Works

Xiaflex contains an enzyme derived from the bacterium Clostridium histolyticum. When injected directly into the Peyronie’s plaque, it breaks down the collagen fibers that form the scar tissue responsible for the curvature. Beyond simply dissolving collagen, the enzyme appears to suppress several disease-related processes at the cellular level, including cell attachment and proliferation, and it may downregulate certain inflammatory signals and growth factors that contribute to plaque formation.¹² The modeling session that follows each injection pair is a key part of the treatment: manually stretching the weakened plaque helps further disrupt it and promotes remodeling during healing.

Does It Matter Whether the Disease Is Still Evolving

A common clinical concern is whether Xiaflex should only be used once Peyronie’s disease has stabilized, the so-called chronic phase. During the acute phase, the plaque is still forming, curvature may be changing, and pain is more common. The worry is that injecting an enzyme into actively inflamed tissue might be less effective or riskier. A single-center retrospective study directly compared outcomes between men treated during the acute and chronic phases and found no meaningful difference. Curvature improvement was nearly identical regardless of disease phase, at about 16% to 17% reduction, and complication rates were similar as well.¹³

This is a single retrospective study, so it is not definitive. But it does suggest that delaying treatment for months while waiting for the disease to stabilize may not always be necessary. For men experiencing significant bother during the acute phase, the data offer at least preliminary reassurance that starting Xiaflex earlier is not clearly less effective. More prospective research on this question would help solidify the guidance, but the early signal is that disease phase alone should not be the deciding factor in whether to begin treatment.

What Drives Men to Choose or Decline Xiaflex

The decision to start Xiaflex is not purely clinical. In a study comparing men who chose Xiaflex with those who did not, the strongest predictors of pursuing treatment were the degree of bother the man experienced and the presence of penile instability during intercourse. Men who chose Xiaflex reported higher scores on psychological distress, pain, and overall bother related to their Peyronie’s disease.¹⁴ Complex curvature patterns also made men more likely to choose injections. In other words, the men most motivated to try Xiaflex tended to be those most affected by the disease in daily life. That seems intuitive, but it also means the men entering treatment are often starting from a higher baseline of distress, which shapes both their expectations and their perception of success or failure.

Cost remains a major barrier. Even with insurance, copays for a full course of Xiaflex can run into thousands of dollars, and some insurers require prior authorization or limit the number of covered cycles. The high discontinuation rate seen in practice, with roughly a third of men not completing all eight injections, reflects these practical realities as much as the drug’s clinical performance. When counseling patients, setting realistic expectations about how many injections may be needed, what degree of improvement is likely given their specific anatomy, and what the out-of-pocket cost will be can go a long way toward reducing frustration and early dropouts.