Advil, Motrin, Propinal—whatever the brand name, all these versions of ibuprofen sold over the counter are pretty much ubiquitous for an easy ache-and-pain remedy. Part of the reason these drugs are a painkiller of choice is because in low doses, they don’t typically have side effects. Nor do they interact strongly with other medications or supplements. Most of us don’t think twice when popping a few pills to ease a headache or cramp.
But ibuprofen may not be so benign for those who take need to take it regularly. A study by researchers working in Denmark found that in doses of more than 1200 mg per day—the maximum recommended amount—ibuprofen disrupts some of the testosterone production pathways in men in as little as 10 days. Testosterone, an important sex hormone in both men and women, is particularly important for sperm production and maintaining erections. The scientists fear that prolonged lower testosterone may inhibit male fertility.
The research published (pdf) the journal PNAS on Jan. 8 included a small trial of 31 men aged 18 to 35 and experiments on cell models. For the clinical trial, 14 men took two doses of 600 mg of ibuprofen per day. The other 17 received sugar pills. Researchers tracked the levels of ibuprofen and hormones in their blood and found that after two weeks, those who had been taking ibuprofen showed signs that their testicles were not making enough testosterone. Specifically, researchers found these men had 23% more luteinizing hormone than the placebo group. This hormone is produced by the brain to signal the testicles to make more testosterone, according to CNN.
Luteinizing hormone can work as a temporary testosterone replacement. But over long periods of time, low levels of testosterone can have adverse effects on the body. “Our immediate concern is for the fertility of men who use these drugs for a long time,” David Møbjerg Kristensen, an environmental health scientist at the University of Copenhagen and lead author of the paper, told the Guardian. Cultures on testis cell tissue confirmed that ibuprofen was the culprit for skewing the levels of these hormones.
The men in the study suffered no permanent damage. Still, the authors are concerned about those who may use high doses of ibuprofen to manage chronic muscle strains or arthritis. This is one of the first studies to look at the long term effects of ibuprofen as a hormone disrupter. It’s not clear at what point suppressing testosterone levels becomes a permanent condition, or has lasting effects on fertility.
It’s still probably safe for men to take ibuprofen over a couple of days for things like a toothache or minor healing injury, Bernard Jégou, an endocrinologist at the French National Institute of Health and Medical Research and author of the study, told the Guardian.
The study’s authors caution that it’s important to remember that ibuprofen is still a drug. Just because it’s available without a prescription doesn’t mean it’s completely risk-free.