Ibuprofen is a common over-the-counter drug that helps with pain and inflammation. (Longer term, lower testosterone would affect this, too.) A few other groups of genes involved in different testicular processes were also unaffected.
This resulted in hypogonadism, which is associated with infertility and increased risk of cardiovascular diseases like stroke and heart failure.
However, Kristensen emphasises that despite the results of the study, men should not stop taking the drug.
Common brands of ibuprofen include Advil and Motrin.
The researchers recruited 31 healthy men between the ages of 18 and 35.
Participants were split into two groups, with 14 receiving 600mg of ibuprofen twice a day two weeks before and 30 days after an exercise session, and the other acting as a control. A control group of 17 men took a placebo instead.
Typically seen in older men and smokers, the condition describes when the testes produce an insufficient amount of testosterone.
'Several studies have shown mild analgesics exposure during foetal life is associated with anti-androgenic effects and congenital malformations. "Using a unique combination of a randomized, controlled clinical trial and ex vivo and in vitro approaches, we report a univocal depression of important aspects of testicular function, including testosterone production, after use of over-the-counter ibuprofen", the paper reads.
Before now, he says, "most warnings regarding this family of painkillers have focused on limiting long-term use in the elderly to prevent gastrointestinal, renal and cardiac adverse effects".
The human brain compensates for testosterone deficiency by producing luteinizing hormone (LH), which sends a signal to the testicles to produce more testosterone.
"However, this is now speculative". It didn't take long - just two weeks - for the drug to disrupt the hormonal balance and rate of testosterone production of these men. "However, it is recommended that if men (or women) need to take it for more than 3 days consecutively then they should first consult their family doctor". However, it remains unknown whether the health effects of long-term ibuprofen use are reversible, he said.