Is it possible that an incredibly common drug ingredient has side effects most users would never expect? A new study suggests that acetaminophen, an ingredient in more than 600 different over-the-counter and prescription medications, makes those who take it not only less sensitive to their own pain, but less empathic to physical and social pain suffered by others. An active ingredient in a slew of brands including Tylenol, Midol, Robitussin, NyQuil, Percocet and Vicodin, acetaminophen is present in drugs taken by 23 percent, or 52 million U.S. adults each week, according to the Consumer Healthcare Products Association.

These new findings contribute to a number of recent studies that suggest there’s plenty about acetaminophen we still don’t know.

Researchers from Ohio State University recruited 80 college students as test subjects. Half were told to drink a solution containing 1,000 milligrams of acetaminophen, while the second half were given a placebo drink containing no drugs. After the medication took effect, the two groups were instructed to rate the pain levels of people in eight different fictional situations; in each case, emotionally or physically traumatic scenarios. One story involved a person forced to deal with a parent’s unexpected death; another a person with a severe stab wound. Researchers found that students who had taken acetaminophen rated the pain levels of the traumatized story characters lower than those who had ingested the placebo liquid.

In another experiment involving 114 students, half drank the acetaminophen solution and the other half were given the placebo. Both groups were then subjected to brief, loud blasts of white noise, and asked to rate the pain levels of a fictionalized participant who had experienced the same. Those who had consumed the acetaminophen solution rated both their own pain, and the pain of others who experienced the noise, lower than those who drank the placebo solution did. In another study section, subjects were shown short videos depicting a person being socially rejected from a group, and were asked to rate the level of emotional pain the rejection caused. Here again, the group that drank the acetaminophen-infused liquid rated the pain lower than those who had only ingested the placebo drink.

"These findings suggest other people's pain doesn't seem as big of a deal to you when you've taken acetaminophen," Dominik Mischkowski, the study’s co-author and a former Ph.D. candidate from Ohio State University said in a news release about the findings. "Acetaminophen can reduce empathy as well as serve as a painkiller."

“We don’t know why acetaminophen is having these effects, but it is concerning,” said Baldwin Way, the study’s lead author and an assistant professor of psychology at Ohio State University. “Empathy is important. If you are having an argument with your spouse and you just took acetaminophen, this research suggests you might be less understanding of what you did to hurt your spouse’s feelings.”

Study authors point to a 2004 scientific investigation in which researchers “scanned the brains of people as they were experiencing pain and while they were imagining other people feeling the same pain.” In both situations, researchers found the exact same area of the brain lit up.

“In light of those results, it is understandable why using Tylenol to reduce your pain may also reduce your ability to feel other people’s pain as well,” Way added.

This isn’t the first study that has found acetaminophen, while useful in treating lots of different aches, may have other unexpected, troubling effects. We’ve long known that taking too much acetaminophen can cause liver damage. Recent studies have found more curious ways the drug may affect those who take it, such as a 2009 analysis that found acetaminophen may lead people to make unduly harsh moral judgments. University of Toronto researchers released a study earlier this year that found compared to a placebo group, people who took acetaminophen were less capable of detecting errors when they saw them. And last year, Baldwin Way was part of a research group that found acetaminophen in Tylenol may blunt takers’ emotional sensitivity overall.

“The core idea of our study is that we don’t fully understand how acetaminophen affects the brain,” said Dan Randles, a postdoctoral fellow and researcher involved in the University of Toronto study.

While all of this is pretty fascinating, and the sum total of this emerging research points to the need for more to be conducted, it’s probably a good idea to avoid full-on panicking about acetaminophen for now.

"In order to come to such a sweeping conclusion, the sample size needs to be in the thousands and needs to be taken out of the insular walls of a college and conducted in the real world," Bola Oyeyipo, a family physician and the founder of Healthgist.com told Greatist.com of the most recent study.

"The bottom line is that further research is still needed on this topic before coming to any definitive conclusions," New York University Hospitalist Group doctor Nesochi Okeke-Igbokwe also told the website.

In upcoming studies, the researchers plan to examine whether other common painkillers, such as ibuprofen, have the same impact, according to Newsweek.