Overusing the most popular illicit substance in the world might make it more difficult to recognize facial expressions in other people, according to new research.
The study, published March 19 in the Journal of Psychopharmacology, found that heavy marijuana consumption was associated with impaired emotional face recognition.
“We aimed to investigate emotional processing deficits, which have previously been observed in cannabis users and which suggest that frequent cannabis users show a generalised impairment in recognising human emotional expression,” Chandni Hindocha of University College London and her colleagues wrote in the study. “Our results shed further light on this impairment and suggest that this deficit cannot be explained by differences between cannabis users and non-using controls in the areas of age, gender, depression nor schizotypy.”
The researchers recruited 25 frequent marijuana users along with 34 non-marijuana using controls. Marijuana use was considered frequent if it occurred more than 20 days per month.
The participants’ ability to assess facial expressions was examined via a computer-based task, in which they were shown male and female faces that portrayed six basic emotions: happiness, sadness, anger, disgust, fearfulness, surprise and neutrality. The 200 facial expressions varied in intensity, and the participants were asked to indicate which emotion the facial expression portrayed as quickly and as accurately as possible.
The researchers found that frequent marijuana users had a harder time identifying the correct emotion compared to the control group, except when it came to surprised faces.
“The fact that surprise was apparently protected against impairment in emotional recognition warrants further research,” the researchers said.
Previous studies have linked heavy marijuana consumption to impaired emotional face recognition, but the research did not controlled some important factors. To eliminate these potentially confounding variables, the researchers recruited an experimental group and control group that did not differ in age, gender, depression, and schizotypy.
The impairment of emotional processing is not unique to marijuana. The heavy use of alcohol, cocaine, heroin, and other recreational drugs has been linked to various deficits in emotional processing as well.
“In summary, our results show that cannabis users displayed a generalised impairment in the ability to recognise and discriminate between emotional faces, and further show that this was not attributable to differences in gender nor schizotypy,” the researcher concluded.
