Latest findings suggest that paracetamol, or acetaminophen, may reduce pleasure as well as pain

Researchers in the US may have uncovered an new side-effect of paracetamol with a study that suggests the drug dampens down people’s emotional reactions.

The over-the-counter pills are among the most popular painkillers on the market, but if the findings are confirmed, it would mean the drug also reduces the sense of pleasure as well as pain.

Scientists have shown before that paracetamol (or acetaminophen) can do more than relieve physical pain. In one study, people who took the drugs felt less emotional pain too, suggesting that similar brain circuits operate for both.

But the latest research, published in the journal Psychological Science, shows that paracetamol may have effects beyond relieving pain, and instead dull our emotional responses more generally.

“Rather than just being a pain reliever, acetaminophen can be seen as an all-purpose emotion reliever,” said Geoffrey Durso, a social psychologist at Ohio State University

Durso gave 82 students either 1000mg of acetaminophen or an identical-looking placebo pill. An hour later - time for the drug to start working - he asked them to look at a series of 40 photographs. These had been selected to trigger strong emotional responses, and included images of distraught malnourished children, or happy children playing with cats.

The students were asked to rate each photo according to how positive or negative the image was, with +5 being the most positive, and -5 the most negative.

After seeing the images once, the students viewed them all again and gave them a second score, this time to indicate the intensity of their emotional reaction to each picture, with zero meaning little or no reaction and 10 indicating an extremely emotional reaction.

The results revealed that those who took paracetamol had less intense reactions to the images, so happy images were seen as less positive, and harrowing images as less upsetting.

“People who took acetaminophen didn’t feel the same highs or lows as did the people who took placebos,” said Baldwin Way, a co-author on the study.

The differences between the groups were not large, however. Students who took the placebo reported an average emotional response of 6.76 when viewing the most distressing or more uplifting images. For those on paracetamol, the average emotional response for the same images was reported as 5.85.

Durso said that he plans follow-up studies to investigate whether other painkillers, such as ibuprofen and aspirin, have the same effect.