Commonly prescribed psychiatric drugs citalopram and levodopa can influence moral decisions about self-harm or inflicting harm on others, according to the results of a study published in Current Biology
on 2 July 2015.
Researchers discovered that the amount of pain people were prepared to anonymously inflict on others or receive themselves in exchange for money varied according to whether they were given the serotonin enhancing antidepressant citalopram or the dopamine-boosting drug levodopa, which is commonly prescribed for Parkinson’s disease.
“We have shown that some of the most commonly prescribed psychiatric drugs influence moral decisions, raising important questions about the ethics of pharmacological interventions,” the researchers say.
“A single dose of citalopram nearly doubled the amount of money people were willing to pay to avoid harming others, whilst a single dose of levodopa eliminated a hyperaltruistic tendency to prefer harming oneself over others.”
The moral-decision study involved 175 healthy adults aged 18-35 years. A total of 89 participants were chosen to receive citalopram or placebo and another 86 received levodopa or placebo.
Individuals were grouped into pairs with one given the role of ‘receiver’ and the other of ‘decider’. All participants were given a mild electric shock that matched their individual pain threshold. Deciders were told that the shocks given would match the individual’s own threshold.
Each decider then sat alone in front of a computer and took part in 170 trials where they were asked to choose between different amounts of money for different numbers of shocks. The maximum number of shocks they could inflict per trial was 20 shocks at a maximum cost of £20.
Half of the decisions related to shocks they were prepared to inflict on themselves and half to shocks to the receiver, but in all cases the decider would be given the money.
The researchers discovered that on average people given placebo were prepared to pay 35p per shock to prevent harm to themselves and 44p per shock to prevent harm to another.
Participants given citalopram were more harm adverse and were prepared to pay an average of 60p per shock to prevent harm to themselves and 73p per shock to prevent harm to another. Individuals in this group delivered on average 30 fewer shocks to themselves and 35 fewer to others compared with the placebo group.
Adults given levodopa were prepared to pay 35p to prevent harm to themselves or to others. They delivered on average ten more shocks than those in the placebo group.
The researchers stress that the drugs probably have different effects in healthy volunteers compared with psychiatric patients. “Future work could usefully investigate how serotonin and dopamine influence harm aversion in psychiatric disorders with monoaminergic abnormalities,” they say.
They think the findings have implications for “potential treatments of social dysfunction that is a common feature as well as a risk factor of many psychiatric disorders”.
Commenting on the study, Lucy Johnstone, consultant clinical psychologist, who is based at Royal Glamorgan Hospital in Llantrisant, Wales, says: “Self-harm is a widespread behaviour in both ‘normal’ and psychiatric populations, and typically performs important psychological functions such as self-punishment, distraction from emotional pain, and the symbolic release of overwhelming feelings.”
Like any other human behaviour it is mediated by biological processes, but is driven and shaped by psychological, social and cultural factors, she adds. “For these reasons I can see no direct role for pharmacology in intervention,” she concludes.
 Crockett MJ, Siegel JZ, Kurth-Nelson Z et al. Dissociable effects of serotonin and dopamine on the valuation of harm in moral decision-making. Current Biology 2015. doi: http://dx.doi.org/10.1016/j.cub.2015.05.021.