Acetaminophen is a common ingredient in pain relievers and has been in use in the United States for over 70 years. The drug's ability to dull psychological pain in addition to physical pain is well documented, but researchers from Ohio State University have discovered another effect — acetaminophen diminishes positive emotions.

Geoffrey Durso, Andrew Luttrell and Baldwin Way detailed their research in a study published in the journal Psychological Science, saying that medication containing acetaminophen reduces an individual's ability to experience feelings. As Durso put it, acetaminophen could be considered an "all-purpose emotion reliever."

According to the trade group Consumer Healthcare Products Association, acetaminophen is so common that it can be found in over 600 types of medicine in the U.S., with 52 million people taking pills containing the ingredient every week.

Durso and his colleagues carried out two studies, involving 82 and 85 participants, respectively. In each case, half received an acute dose of 1,000 milligrams of acetaminophen and the rest received a placebo. They were then asked to view and rate a series of images ranging from extremely negative to extremely positive content.

In the first study, the team discovered that participants given acetaminophen did not feel the same highs and lows as those who were administered placebos. On a scale of 0 to 10, the average emotional levels for the acetaminophen group remained at 5.85 when viewing photos capable of eliciting extreme emotions from the control group.

Wanting to confirm that the dulled response was linked to emotions – rather than influencing broader judgment – they conducted a second experiment, introducing a new element. Subjects were again made to view images and rate how they felt, but this time, they also had to report how much of the color blue they saw in each photo.

The same level of blues was observed by those given acetaminophen and those taking placebos. The researchers thus concluded that the pain-relieving ingredient affects emotional evaluation, not magnitude judgments.

Researchers are not yet sure whether other pain relievers, like aspirin and ibuprofen, produce the same results. It's also unclear if the fact that acetaminophen is not a nonsteroidal anti-inflammatory drug (NSAID) has a role in the side effects.

In any case, the results of the study could have big implications for psychological theory, supporting a new idea proposing common factors have an influence on how people are affected by both good and bad experiences.

"There is accumulating evidence that some people are more sensitive to big life events of all kinds, rather than just vulnerable to bad events," added Durso.

Photo: David Pacey | Flickr

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