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Painkillers could be one of the reasons why male fertility is at a tipping point. Last year, scientists found out that sperm counts in western countries had declined by 50 percent in less than 40 years.

Though the exact reasons for the decline are not yet known; in a recent study, researchers have linked male infertility to Ibuprofen – a common painkiller.

The study shows that it has a negative impact on the testicles of young men, altering their sex hormone production and affecting their reproductive health. Prolonged use of the drugs can even diminish their sex drive.

Researchers studied 31 healthy men aged between 18 and 35 who took the common painkiller for up to six weeks and found that the drug disrupted the production of male sex hormones -- a condition that's normally seen in older men and smokers.

Levels of luteinising hormone, which stimulates the testosterone production increased in the study participants but overall testosterone dropped.

The disorder called "compensated hypogonadism" developed in the study participants within two weeks of having 600mg of ibuprofen twice a day.

"Our immediate concern is for the fertility of men who use these drugs for a long time," researcher David Møbjerg Kristensen from the University of Copenhagen in Denmark told The Guardian.

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"These compounds are good painkillers, but a certain amount of people in society use them without thinking of them as proper medicines," he added.

While this effect wasn't permanent, the researchers warned that prolonged use of ibuprofen by men could lead to low testosterone production – which might end up harming their fertility.

"In the living body the pituitary gland kicks in to compensate for this, but the brain is pushing more to get the same amount of testosterone," Kristensen said. "If you go on and stress the pituitary gland over the long term, this state could become permanent and you develop a more serious condition."

Bernard Jégou, a senior author on the study at the French National Institute of Health and Medical Research, said that he believes that there is no problem in people taking ibuprofen to alleviate pain in the short term but he warns against taking the drug for months on end if it was not absolutely necessary.

"We normally see this condition in elderly men, so it raises an alarm," Jégou said. "We are concerned about it, particularly for healthy people who don't need to take these drugs. The risk is greater than the benefit."

The study is published in the journal Proceedings of the National Academy of Sciences.