The popular over-the-counter painkiller ibuprofen, widely used for aches and pains, could make young men infertile by shrinking their balls, scientists have warned.

The drug that costs just 2p for a 200mg tablet lowers the male sex hormone testosterone.

The drop in the hormones produced by the testicles then causes them to shrivel up causing fertility problems.

A study of 18 to 35 year-olds found the painkiller increased the risk of the disorder compensated hypogonadism which usually only affects the elderly or smokers.

Overuse of ibuprofen could also lead to full-blown hypogonadism- or low testosterone levels - which has been linked to premature death.

The study of 31 male participants found the administration of ibuprofen reduced production of testosterone by nearly a quarter in about six weeks - resulting in compensated hypogonadism. In experiments on testicles from prostate cancer donors and cultured testes cells the researchers found ibuprofen induced the condition by affecting hormones.

Dr David Kristensen, of Copenhagen University, said: "Ibuprofen appears to be the preferred pharmaceutical analgesic for long-term chronic pain and arthritis.

"Therefore it is also of concern that men with compensated hypogonadism may eventually progress to overt primary hypogonadism, which is characterised by low circulating testosterone and prevalent symptoms including reduced libido, reduced muscle mass and strength, and depressed mood and fatigue."

Previous research has found an association between low testosterone levels and premature death from heart disease and all causes.

A study of almost 1,000 men tracked for seven years found almost twice as many with testosterone deficiency - or hypogonadism - died as did those with normal levels.

Compensated hypogonadism occurs before any obvious sypmtoms develop.