"Regular non-steroidal anti-inflammatory drug use is associated with erectile dysfunction beyond what would be expected due to age and other conditions," he says.

More than 30 million people a day take these prescription and over-the-counter pain relievers.

The observational study, which began in 2002, included 80,966 men ages 45 to 69 who were members of Kaiser managed care plans in California. Erectile dysfunction was assessed by questionnaire and NSAID use was determined using pharmacy records and self-reported data.

Regular users were about 2.4 times more likely to have erectile dysfunction than men who didn’t use those drugs regularly or at all. Even when the scientists controlled for age, race and ethnicity, smoking, diabetes, hypertension, high cholesterol, and coronary artery disease among other health problems, a link between NSAID use and erection problems still existed, said Jacobsen.

A previous smaller study suggested a similar link, but Jacobsen says it’s too early to conclude that ibuprofen is the reason for erectile dysfunction. He says that the drugs have many proven benefits, and that men whose doctors have prescribed NSAIDs for other reasons shouldn’t cut them short.

The results raise more questions than they answer, says Stephen Kraus, professor and vice chairman of urology at the University of Texas Health Science Center at San Antonio.

He says NSAIDs have been shown to reduce risk of heart disease, so the same should be true of erectile dysfunction, which can be linked to circulation problems. "If it works for one, you’d think it should work for the other. But lo and behold, the opposite is what they saw in this study. The question is why?" Kraus says.

The study authors suggest several theories, including that while treating someone to improve blood flow may potentially make erections better, it could also hinder other pathways involved in healthy erectile function.

"It needs to be tested in a clinical trial designed to look at this," Kraus says. He agrees it’s premature for men to avoid NSAIDs based solely on this new research.