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Acetaminophen may dull your emotions

Chances are, if you suffer from occasional aches and pains, you probably have a bottle of acetaminophen in your medicine cabinet.

This pain reliever most people know as Tylenol can help a headache, ease chronic joint or body pain, and reduce a fever. But one thing most people don't realize is that along with physical pain, acetaminophen may also dull emotions.

A new study published in the journal Psychological Science suggests this popular drug could dampen a person's emotions -- both good and bad. This may be related to the fact that pain travels from injury through nerve signals and affects serotonin and other chemicals that control emotional response.

"What I found fascinating about this study is we've known for a while that in addition to relieving pain, Tylenol also may blunt our negative emotions, or our emotional pain," medical contributor Dr. Holly Phillips told "CBS This Morning." "This study took it a step further and said that in addition to affecting negative emotions it may also affect positive feelings as well."

The paper reports the findings of two small studies. The first one involved 82 people, half of whom took 1,000 milligrams of acetaminophen -- the active ingredient in Tylenol -- while the other half got a placebo. The researchers waited an hour and then showed the participants 40 photographs, many of which would typically elicit strong emotions, either positive or negative, such as photos of crying, malnourished children, or young children playing with cats. What they found was that, compared with people who took a placebo, those who had taken acetaminophen had a less strong reaction across the board to both negative and positive images.

"This study didn't establish what the cause is, but we know that pain is not a local phenomenon," said Phillips. "If you have pain in your knee it's not just there. It affects nerve receptors there but then that moves to nerve tissue, the central nerve system and parts of your brain that affect emotion, but importantly that affect positive and negative emotions. So if you might relieve negative feelings, you also may relieve those positive feelings as well."

For a second study, the researchers showed 85 people the same photos and asked how they felt. Those who took acetaminophen also reported reduced emotional reaction. They were also asked to report how much blue color they saw in each photograph, a non-emotional question, and in that case both the acetaminophen and control groups reported the same.

Phillips said that while this research is still quite preliminary, it is worth paying attention to since the drug is so widely popular: 1 in 5 people in the U.S. take acetaminophen at least one time each week. Unlike other over-the-counter painkillers like aspirin or ibuprofen, acetaminophen is not a nonsteroidal anti-inflammatory drug, or NSAID, which means the drug most likely targets pain receptors in the body rather than inflammation.

"It is a little bit of a red flag for people who take it every day. You don't want to blunt feelings of happiness," said Phillips.

She added that in addition to impacting emotions, longterm and frequent use of the drug may cause some physical health problems such as liver failure. Currently the U.S. Food and Drug Administration recommends a person take no more than 3,000 milligrams of acetaminophen within 24 hours, or no more than two pills every six hours.

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    Jessica Firger covers health and wellness for CBSNews.com