Some non-surgical methods for increasing the length of the male sex organ do in fact work, while others are likely to result only in soreness and disappointment, a review of medical literature has shown.

Surgical procedures, however, can be dangerous and have an "unacceptably high rate of complications," according to the study, published this week in the Journal of the British Association of Urological Surgeons.

"An increasing number of patients seek urological advice for the so-called ’short penis’," the researchers reported.

This is true despite the fact that "penile length is normal in most of these men, who tend to overestimate normal phallic dimension."

A male member — measured on the dorsal, or upper, side — can be considered normal in length if it is at least four centimeters (1.6 inches) when limp, and 7.5 centimeters (three inches) when rigid, noted several of the studies evaluated.

Some allowances, they added, must be made for a man’s height and his body-mass index (BMI), which measures deviation from optimal levels of body fat.

To determine the efficacy and safety of both surgical and non-surgical techniques for so-called "male enhancement," Marco Orderda and Paolo Gontero of the University of Turin in Italy canvassed scientific literature.

They found 10 relevant studies. Half reported on surgical techniques, performed on 121 men.

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 centimeters (0.7 inches), while another measured an extra 2.3 centimeters (0.9 inches) in a flaccid state, and 1.7 centimeters (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.

Another device, known as a "penis pump," uses a manual or motorized pump to create a vacuum inside a hard cylinder sheath, stretching the phallus.

Six months of treatment, however, "was not found to be effective for penile elongation, although is provided some sort of psychological satisfaction for some men," the researchers said.

So-called peno-scrotal rings — expandable or rigid bands that fit around the base of the scrotum and penis — "might help to augment penile size and maintain erections in men suffering from anxiety", they reported, but only two cases were evaluated.

Advertisements claiming that another popular technique — so-called "penile lengthening exercises" — can add centimetres or inches to one’s manhood are unfounded, say Oderda and Gontero.

Even the methods that did show some increase in length did not result in a gain in thickness, they noted.

But nor was their shrinkage.

"It is interesting that no girth decrease was reported with traction therapy, as one would have instinctively thought," the researchers said.