Gontero, Levine, Haney and more: an honest review of 15 years of penile traction therapy studies — what they show, and where the evidence thins out.
If you’re considering traction therapy, you deserve to know what the research actually says — not the marketing version. Here’s every major study, what it found, and what it didn’t.
Let’s start with two promises about this article. First: nothing here is a trial of any product. The studies below tested traction therapy as a general approach — mostly in men with Peyronie’s disease, a fibrotic condition of the penis — using various devices over the past fifteen-plus years. Research on a category of therapy is not research on any specific device, and no article on this site will ever blur that line. Second: we’ll show you the weak spots, not just the highlights. A literature review that only quotes the good news is an advertisement wearing a lab coat.
With that said — what does the clinical literature actually show?
If you want the details behind each of those sentences, read on.
The proposed mechanism has a name — mechanotransduction — and a 2025 narrative review of the field describes it as the founding principle behind traction therapy: cells sense sustained mechanical force and respond by remodeling tissue, encouraging fibroblast proliferation and reorganizing disordered collagen fibers (Cureus, 2025; PMC12641373).
In plain terms: pull gently on connective tissue for long enough, and the cells inside may start clearing out old collagen and laying down new fibers aligned with the direction of the pull. It’s the same logic behind orthodontic braces and surgical tissue expanders — both covered in depth in our companion piece on tissue conditioning.
The key word is proposed. Mechanotransduction is well established as a cell-biology phenomenon; whether it explains every centimeter reported in traction studies is exactly what the clinical data has been trying to pin down since 2008.
The study most reviews cite first comes from the University of Turin, and its title alone tells you the authors were being careful: “A pilot phase-II prospective study to test the ‘efficacy’ and tolerability of a penile-extender device in the treatment of ‘short penis'” — with “efficacy” in scare quotes (Gontero et al., BJU Int. 2009;103:793–797; PMID 18990153).
Fifteen men used a commercial extender for at least 4 hours a day over 6 months. At the six-month mark, the average gain was +2.3 cm flaccid and +1.7 cm stretched — statistically significant, in a study powered to detect exactly that kind of effect. Girth didn’t change significantly. Erectile-function scores improved.
What to make of it: it’s the largest reported length gain in the literature — and also one of the weakest designs. Fifteen men, no control group, no blinding. The authors called it a pilot, and “pilot” is doing a lot of work in that sentence: it means “interesting enough to justify a real trial,” not “case closed.” In evidence-based medicine, this is Level 4 evidence — a case series.
Urologist Laurence Levine’s group in Chicago ran their pilot in a different population: men with Peyronie’s disease, the fibrotic condition that causes penile curvature (Levine et al., J Sex Med. 2008;5:1468–1473; PMID 18373527).
Ten men completed the study (eleven enrolled), using an extender for 2–8 hours a day over 6 months. The headline results: curvature reduced by an average of 33% (from 51° to 34°), stretched length increased 0.5–2.0 cm as objectively measured — patients themselves estimated up to 2.5 cm, a useful reminder that self-reports run hot — erect girth increased 0.5–1.0 cm, and the “hinge effect” (instability during erection) resolved in all four men who had it. Erectile-function scores rose from 18.3 to 23.6. No adverse events were reported: no skin changes, ulcerations, numbness, or loss of rigidity.
What to make of it: encouraging, especially on curvature — but again, ten men and no control group. In an uncontrolled study, you can’t separate the device’s effect from placebo, natural history, or the simple fact that people who sign up for a six-month daily regimen are unusually motivated.
This is the study everything else gets measured against. In 2019, Mayo Clinic investigators published the first — and still only — randomized, single-blind, controlled trial of traction monotherapy: 110 men with Peyronie’s disease, randomized 3:1 to traction with a modern device or a no-treatment control group, for 30–90 minutes a day (Ziegelmann et al., J Urol. 2019;202:599–610; PMID 30916626).
At three months, the traction group showed +1.5 cm length versus 0 cm in controls (p<0.001), −11.7° curvature versus +1.3° (p<0.01), and meaningful erectile-function gains. Overall, 94% of treated men gained length (mean +1.6 cm) and 77% saw curvature improve (mean −17.2°). Adverse events were mild and transient; none caused anyone to stop treatment. Mean actual use was just 43 minutes a day — a fraction of the multi-hour regimens older studies demanded.
What to make of it: this is genuinely the best-designed evidence in the field — randomized, controlled, blinded assessment. Two honest asterisks: the primary endpoint was at three months (short), and all participants had Peyronie’s disease, so it tells us about traction as a therapy for a condition, not about enhancement in healthy men. Still: if you take one study from this article, take this one.
When individual studies are small, researchers pool them. Haney and colleagues performed a systematic review and meta-analysis of traction used after primary Peyronie’s treatment — surgery or injections — asking whether add-on traction preserved length better than the primary treatment alone (Haney et al., Urology; PMID 30099127; summarized in Valenzuela et al.’s 2019 review, PMC6444402).
Four studies, 348 men (171 traction, 177 control): the traction groups ended up +1.02 cm ahead on stretched length [95% CI 0.64–1.40; p=0.009].
What to make of it: a statistically significant pooled result — and a perfect case study in why “statistically significant” isn’t the same as “settled.” The review that summarized this meta-analysis flagged the limitations plainly: heterogeneous patient populations, varying concurrent treatments, selection bias (most included studies weren’t randomized), poor compliance — and, crucially, gains of questionable clinical significance. A centimeter is real on a ruler; whether it matters to a patient is a separate question the data can’t answer for you. And note the context again: this was traction after surgery or injections, not standalone traction.
The most recent comprehensive look — a 2025 narrative review spanning publications from 2009 to 2025, fifteen major studies, over 1,000 patients — lands roughly where you’d expect (Cureus, 2025; PMC12641373):
A narrative review isn’t a meta-analysis — it summarizes rather than pooling statistics — but as a state-of-the-field snapshot, it’s the best single document to read if you read one.
This is the section most articles like this skip. We won’t.
The samples are tiny. Two of the foundational studies enrolled fifteen and ten men. You could fit every participant in a minivan. Small studies are more vulnerable to chance, to outliers, and to the enthusiasm of the researchers running them.
There is exactly one randomized controlled trial — the RestoreX study — with a three-month primary endpoint. Everything else is pilots, case series, and retrospective comparisons. In evidence-based medicine, that’s the bottom half of the ladder.
The populations don’t match the question most readers are asking. Nearly all the data comes from men with Peyronie’s disease or post-surgical patients. If you’re a healthy man curious about traction, you’re extrapolating from people with a fibrotic condition — related tissue, different starting point.
The protocols are all over the map. Two to nine hours a day in older studies; 30–90 minutes in newer ones. When the “dose” varies tenfold between studies, pooling their results is an act of faith as much as statistics. Compliance tells the same story from the other side: in one analysis, only about 40% of men managed the prescribed three hours a day — and the men who wore the device longer tended to gain more, which suggests dose matters, but also that these regimens select for the most motivated patients.
Adverse events are probably underreported. The published literature describes mostly mild, transient issues — temporary pain (reported in up to a quarter of men in some series), redness, bruising, itching, numbness. But small studies with motivated volunteers are exactly where side effects get minimized. The honest statement is: serious harm looks rare; minor irritation looks common; and nobody has run the large, long trial that would settle it.
Publication bias is almost certain. Studies that find nothing tend not to get published. The literature you can read is pre-filtered for positive results.
Here’s our honest read, after walking through all of it:
We’ll keep this review updated as new studies publish. Science moves; so should honest summaries.
You might wonder why a company that sells a traction device would publish a review that spends half its words on limitations. Because this industry lies too much. Miracle pills, photoshopped before-and-afters, “guaranteed inches” — the noise is so loud that the actual science, modest as it is, gets drowned out.
We believe honesty is the better long-term strategy. We’d rather lay the evidence out — the gains and the gaps, the promising signals and the thin data — and let you judge for yourself. A customer who buys with clear eyes is worth ten who buy on hype. That’s why we write about the science the way we’d want someone to write it for us: carefully, completely, and without hiding the parts that are inconvenient.
Curious how these principles translate into a structured at-home protocol? Learn more about the Jumbo System →
This article is for informational purposes only and is not medical advice. If you’re considering any traction therapy, speak with a qualified urologist first.