The opioid system of the brain contributes to the regulation of emotions, pleasure and pain. Opioids are strong painkillers that impact this system. It has been assumed that in addition to effectively relieving pain, opioid use in the short term can improve the mood and reduce negative emotions. However, not much has been known about the effect of opioids on emotional responses caused by external stimuli.
Together with their colleagues from Aalto University and the University of Turku, researchers from the University of Helsinki and the Hospital District of Helsinki and Uusimaa have examined the effect of remifentanil, an opioid, and naloxone, an opioid agonist, on emotions which study subjects experienced when viewing various film clips. A total of 31 healthy adult men aged between 20 and 35 years took part in the study.
The study subjects completed a questionnaire used to assess their subjective emotionality, after which they were intravenously administered remifentanil, placebo and naloxone for successive tests. The subjects did not know the order in which the substances were administered.
During each infusion, they viewed ten film clips, some of which were pleasant and others unpleasant, after which they evaluated the emotions of pleasure and emotional arousal caused by the clips.
“Remifentanil significantly increased the experience of pleasure caused by the film clips, but not feelings of emotional arousal. The increase in pleasure was evidenced in the assessment pertaining to both unpleasant and pleasant clips,” explains Tarja Heiskanen, MD, a specialist in anaesthesiology at the Hospital District of Helsinki and Uusimaa.
In the case of naloxone, evaluations of emotional experiences were more neutral, but the effect was minor and different from the effect of the placebo only to an insignificant degree.
“It appears that short-term opioid use increases the positivity of emotional experiences by intensifying feelings of pleasure and decreasing negative emotional experiences. This may be among the factors resulting in the onset of dependence right after the first instances of opioid use,” Heiskanen notes.
“All in all, our findings indicate that emotional responses to external stimuli occur through the endogenous opioid system.”
What the researchers emphasise is that the effect of opioids on emotional responses and mood changes is different when the drug is used for a longer period.
“Prolonged opioid use alters the reward system of the brain, diminishing its sensitivity. The ability of humans to experience pleasure caused by external stimuli becomes numb, which, in turn, increases depression risk.”
Tarja Heiskanen, MD, specialist, Hospital District of Helsinki and Uusimaa
Phone: +358 50 427 2386
Reference: Tarja Heiskanen, Mika Leppä, Juulia Suvilehto, Minna Elomaa, Ethem Akural, Tekla Larinkoski, Iiro Jääskeläinen, Mikko Sams, Lauri Nummenmaa, Eija Kalso. The opioid agonist remifentanil increases subjective pleasure. British Journal of Anaesthesia. Doi.org/10.1016/j.bja.2019.03.031