Painkiller or Pleasure Killer? Paracetamol’s hidden effects

[box] Rob Cleaver reports on new research from the US that suggests it isn’t just pain that paracetamol is killing. [/box]

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A study by researchers at Ohio State University in the USA have found that paracetamol may dampen down normal human emotions.

Used by millions on a daily basis, paracetamol (or acetaminophen in the US) is one of the most well known and widely used painkillers available over the counter in the United Kingdom. Paracetamol is known to be a cyclooxygenase 2 (COX-2) inhibitor but little is known about its neurochemical effects within the brain and previous studies had suggested that paracetamol may exhibit an effect upon psychological processing.

The team at Ohio State, headed by Geoffrey Durso, a social psychologist, recruited 82 students for their study. Half of the participants took 1g paracetamol and the others took an identical in appearance placebo pill. Sixty minutes after taking the tablets, the participants were encouraged to look at the same 40 photographs from the International Affective Photograph System, a collection of photographs used to elicit a wide variety of emotional responses. The images contained both strongly negative stimuli, such as malnourished children, and strongly positive ones, such as children playing with animals. The participants were asked to record how positive or negative each image was on a scale from +5 to -5. After seeing each image once, they were then asked to look at each photo a second time and rate on a scale from 0 (no emotion) to 10 (strong emotion how strong their emotional response was.

The results from the study showed that those who had taken paracetamol generally had a more blunted emotional response to both negative and positive stimuli compared to those who had taken the placebo. They also found that the paracetamol group rated positive images as being less positive and negative images less negative when compared to the placebo cohort. The team conclude that this is the result of paracetamol exerting a general effect on one or more psychological evaluative processes potentially via its known effects on the serotonergic system through which its analgesic effects take hold.

What this means for the behaviours of those needing pain relief is yet to be seen but future research by the team aim to evaluate whether other painkillers such as ibuprofen have similar effects upon emotion.

The original publication in Psychological Science can be found here.

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