A new US study has shown that taking drugs which include acetaminophen, such as the common painkiller Tylenol, can not only dull your pain but also your empathy towards the pain of others.

Researchers at The Ohio State University found that when participants who had taken acetaminophen learned of other's misfortunes they rated the pain and suffering of these individuals as lower than participants who had taken no painkiller.

And the results were the same whether the pain was physical or emotional, with participants rating the pain of those in the different scenarios to be less severe whether it was a knife cut that went down to the bone or the death of a parent.

The study's lead author Baldwin Way had also found in a previous study that as well as dulling empathy, acetaminophen can also dull positive emotions such as joy, with the results of the two studies suggesting there is more to the drug than simply pain relief.

"We don't know why acetaminophen is having these effects, but it is concerning," commented Way, "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."

However Way also added that although the findings were new they were not a complete surprise, with a 2004 study showing that the brains scans of people experiencing pain showed that the same part of the brain was activated as those who were imagining other people feeling the same pain.

"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," he said.

Way and his team are now not only continuing to research how acetaminophen may affects people's emotions and behavior, but also looking at another common over-the-counter drug -- ibuprofen -- to see if it has any similar results.

As well as being the main ingredient in the painkiller Tylenol, acetaminophen is the most common drug ingredient in the United States, found in more than 600 medicines and taken by around 23 percent of American adults (about 52 million people) each week, according to the trade group Consumer Healthcare Products Association.

The findings were published online in the journal Social Cognitive and Affective Neuroscience.