Among the non-invasive methods, tested on 109 subjects, so-called penile extenders that stretch the phallus through traction were shown to be most effective.

One study reported an average increase of 1.8 centimetres (0.7 inches), while another measured an extra 2.3 centimetres (0.9 inches) in a flaccid state, and 1.7 centimetres (0.67 inches) when erect.

But the regimen for achieving these gains was arduous: six hours of daily traction over four months in the first case, and four hours every day over six months in the second.