Male fertility could be at a tipping point. Last year, scientists discovered sperm counts in western countries had plummeted by 50 percent in 40 years, and while the reasons behind the decline are complex, many researchers say the phenomenon is due to men's hormones being disrupted.

Now, one of those disruptors has come to light. In a new study, scientists show the common painkiller ibuprofen can have a negative impact on testicular health, altering hormone production and inducing a condition called compensated hypogonadism, which affects reproductive health in men.

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

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

While previous research had already demonstrated that foetal exposure to ibuprofen and other analgesics (like aspirin and paracetamol/acetaminophen) could be harmful, less was known about its potential effects on adult men.

To find out, researchers recruited 31 male participants aged between 18 and 35, giving half of them a moderate dose (600 milligrams, equivalent to three tablets) of the drug daily for six weeks, while the other group took a placebo.

For context, up to 3,200 mg per day is considered the maximum daily adult limit by some medical sites. But even a small fraction of that dosage had a negative effect on the men after two weeks of daily use.

Within 14 days, the men taking daily ibuprofen exhibited an increase in luteinising hormones – which help regulate testosterone production – indicating the drug had impaired healthy testicular function, forcing the body to compensate by boosting testosterone levels.

While this effect wasn't permanent, the researchers warn prolonged use of ibuprofen by men could potentially progress to more serious conditions causing low testosterone production – which might end up harming their fertility.

"[I]t 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," the team writes.

While researchers are welcoming the findings, they also say the most alarming outcomes are unlikely for most people. Also, given the results come from such a small sample, more research is definitely needed.

"Further studies are required to investigate whether this mild effect of ibuprofen could significantly impair testicular function in terms of testosterone levels, or fertility, after long term use – this study did not examine effects on fertility," explains endocrinologist Ali Abbara from Imperial College London, who wasn't involved in the study.

"The effects were very mild even after six weeks of regular consumption of ibuprofen, which is longer than is usually recommended in practice, so this data should not concern men who occasionally take ibuprofen for pain relief."

As for those whose use isn't so occasional? The results aren't yet clear.

But given how athletes routinely use the medication to help with recurring sports injuries, experts say this is something we definitely need to stay aware of – because despite how some might abuse it, ibuprofen isn't something that was ever intended to be taken casually.

"[T]he alarm has been raised now," one of the team, Bernard Jégou from the Institute of Research in Environmental and Occupational Health in France told CNN.

"[I]f this serves to remind people that we are really dealing with medical drugs – not with things which are not dangerous – this would be a good thing."

The findings are reported in Proceedings of the National Academy of Sciences.