Paracetamol does more than just alleviate aches and pains – increasing evidence suggests it also affects emotions.

In previous studies, paracetamol was found to blunt “hurt feelings” arising from social relationships and negativity around thoughts of personal mortality.

Now new research suggests that paracetamol “has a previously unknown side-effect” of blunting positive emotions.

“Rather than just being a pain reliever, [paracetamol] can be seen as an all-purpose emotion reliever,” says lead author Geoffrey Durso, from Ohio State University. Researchers enrolled 82 college students, half of whom took 1,000mg paracetamol and half placebo. Sixty minutes later, participants viewed 40 photographs ranging from extremely unpleasant (crying, malnourished children) to neutral (a cow in a field) to very pleasant (young children playing with cats).

Participants rated each photo on scales of – 5 (extremely negative) to +5 (extremely positive) and from 0 (little or no emotion) to 10 (extreme emotion). Evaluations by paracetamol users were blunted (i.e. less positive and less negative) than those in the placebo arm. The same happened with emotional reactions.

The average emotion score was 6.76 among placebo users when they saw the most emotional photos, compared to 5.85 among paracetamol users. Paracetamol did not seem to influence how patients viewed neutral photos. The researchers then asked another 85 students to view the same photos, make the same judgments and report how much blue they saw in each picture.

Again, paracetamol users showed blunted evaluations and emotional reactions to the negative and positive images, but their judgments of the blue content were similar. This suggests that paracetamol affects emotional evaluations and not judgments of magnitude in general. The researchers now plan to study whether other analgesics, such as ibuprofen and aspirin, produce the same effect.

Future research also needs to determine the neurochemistry (e.g. serotoninergic or inflammation) underlying the effect. (Psychological Science doi:10.1177/ 09567976 15570366)