What are the measured average length gains reported in randomized trials of penile traction devices?

1. RestoreX randomized trials: about 1.5–1.6 cm on average

A randomized, single‑blind trial of the second‑generation RestoreX device in men with Peyronie’s disease reported a mean length increase of about 1.5–1.6 cm at the randomized 3‑month endpoint compared with essentially no gain in controls, with 94% of users experiencing some length increase and roughly 10.9% gaining ≥1.6 cm in that trial’s analyses (mean 1.5 cm at 3 months; 1.6 cm reported in open‑label follow up and post‑prostatectomy trials) ^{[1] [2] [3]}. A post‑prostatectomy randomized, controlled single‑center study using RestoreX found preservation or improvement of penile length of +1.6 cm versus +0.3 cm in controls at 6 months ^[3].

2. Earlier and lower‑dose trials: gains often smaller, sometimes under 1 cm

Older or lower‑dose protocols and nonrandomized studies reported smaller average gains; for example, studies where devices were worn for multiple hours daily over longer spans reported mean stretched penile length increases around 0.5–0.8 cm in some cohorts, and a trial that compared ≥3 hours/day usage to less or no traction found a significant advantage measured in millimetres (about 4.4 mm vs 1.3 mm) ^{[6] [4]}. Pilot and phase‑II reports of other extenders showed variable absolute changes, with some flaccid‑length increases reported up to ~2.3 cm at longer follow‑up in uncontrolled series but these were not randomized RCT results ^{[7] [8]}.

3. Systematic reviews and contemporary summaries: consistent modern-device signal of ~1.5–2.0 cm

Narrative reviews and systematic summaries conclude that modern traction therapies and contemporary devices tend to show length restoration in the ballpark of 1.5–2.0 cm across pooled and device‑specific reports, emphasizing recurring findings in RestoreX and similar devices while noting heterogeneity across studies ^{[5] [9]}. These reviews explicitly call out that device features, adherence, and treatment duration are major drivers of effect size and patient satisfaction ^[5].

4. Why reported gains vary: measurement, population and protocol differences

Reported average gains differ because trials use different populations (Peyronie’s disease, post‑prostatectomy patients, men seeking primary lengthening), different outcome measures (flaccid, stretched or erect length), different daily wear times (minutes versus hours), different total durations (3–12 months) and variable study quality and sample sizes; these methodological differences explain why a modern RCT reports ~1.5 cm while older or lower‑dose studies report subcentimetre gains ^{[1] [3] [4] [6]}.

5. Limitations and how to read the numbers

Most randomized data come from modestly sized trials (dozens to low hundreds), short to mid‑term endpoints (3–6 months) and devices with differing mechanics, so the headline “~1.5 cm” should be read as an approximate range for modern, guided PTT protocols rather than a guaranteed or universal outcome; long‑term durability, optimal wear‑time dose and direct comparisons across devices remain incompletely settled in randomized data ^{[2] [3] [5]}.

6. Balanced takeaway for evidence‑based framing

Randomized evidence for contemporary devices consistently shows measurable, statistically significant length gains versus no therapy—with most high‑quality modern trials clustering around ~1.5–1.6 cm over months of regular use—yet smaller or nonrandomized studies report more modest millimetre‑scale gains and methodological differences mean individual results will vary and more large, standardized RCTs are needed to define dose, duration and durability ^{[1] [3] [4] [5]}.