Cocaine users display worse memory performance, concentration difficulties, and attentional deficits. They have difficulties understanding the perspective of others, show less emotional empathy, find it more difficult to recognize emotions from voices, behave in a less prosocial manner in social interactions and report fewer social contacts.

So why is it the second most popular drug in Europe, after marijuana? 

Scholars at the Psychiatric Hospital of the University of Zurich say the worse emotional empathy was correlated with a smaller social network and the social cognitive deficits contribute to the development and perpetuation of cocaine addiction.

Psychologists Katrin Preller und Boris Quednow, Head of the Division of Experimental and Clinical Pharmacopsychology at the Psychiatric Hospital of the University of Zurich, conclude that impaired social interaction skills of cocaine users could be explained by a blunted response to social reward. The team say that cocaine users perceived joined attention – the shared attentional focus of two persons on an object after gaze contact – was less rewarding compared to drug-naive healthy controls.

In a subsequent functional imaging experiment they showed that cocaine users showed a blunted activation of a crucial part of the reward system – the so called medial orbitofrontal cortex – during this basal kind of social interaction. Interestingly, a weaker activation of the medial orbitofrontal cortex during social gaze contact was also associated with fewer social contacts in the past weeks.

Quednow explained, "Cocaine users perceive social exchange as less positive and rewarding compared to people who do not use this stimulant."

They propose that changes in brain function might help to explain why dependent cocaine users often fail to stop using drugs despite the occurrence of severe social consequences such as familial problems, loss of friends or employment.

Reduced reward during social interactions might also explain why many cocaine dependent individuals loose supportive social contacts during the course of their drug career, which probably further contributes to the maintenance of addiction.

Given that social reward is important for successful psychotherapy, Preller and Quednow suggest, "Social skills, such as empathy, mental perspective taking, and prosocial behavior, should be trained during the treatment of cocaine dependence to enhance the efficacy and sustainability of the treatment."