Drug users often find it difficult to identify between right and wrong. (Representational Image)
Regular drug users may have difficulty choosing between right and wrong because the parts of their brains used for moral processing and evaluating emotions are damaged by their prolonged narcotic habits, a new study suggests.
Research has shown that stimulant users often find it difficult to identify other people's emotions, particularly fear, and to show empathy.
These aspects play an important role in moral decision making, researchers said.
Other studies have pointed to structural and functional abnormalities in especially the frontal regions of their brains among stimulant users.
These areas are engaged when moral judgements have to be made, they said.
"This is the first study to suggest impairments in the neural systems of moral processing in both cocaine and methamphetamine users," said Samantha Fede from University of New Mexico.
Poor judgement about moral situations can lead to poor decision making and subsequent antisocial behaviour, researchers said.
They recorded the life history of substance abuse of 131 cocaine and methamphetamine users and 80 non-users incarcerated in New Mexico and Wisconsin prisons.
The participants' brains were scanned while they completed a moral decision-making task in which they evaluated whether certain phrases were morally wrong or not.
Compared to the non-users, the regular stimulant users had abnormal neural activity in the frontal lobes and limbic regions of their brains during moral processing.
Specifically, lifetime stimulant users showed less activity in the amygdala, a group of neurons in the brain that helps to regulate and understand emotions.
Researchers also observed a relationship in the level of engagement of the anterior cingulate cortex: the longer people had been using stimulants, the less activity in this region.
This is an area of the brain that coordinates reinforcement, effect and executive action needed in moral decision making.
The effects found related to use over time in the anterior cingulate cortex and the ventromedial prefrontal cortex, another region implicated in moral decision making, indicate that methamphetamine and cocaine may have a serious impact on the brain, researchers said.
The findings were published in the journal Psychopharmacology.
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