The Most Popular Psychiatric Drugs Alter Decisions to Cause Harm

Citalopram (Celexa®) and levodopa (Larodopa®), considered to be the most commonly prescribed antidepressant and Parkinson’s drug respectively, have been shown in a new study to alter how healthy individuals make moral decisions to harm both oneself and other people. Conducted by researchers from UCL and Oxford University the research investigated how taking citalopram or levodopa altered participants’ decisions to inflict pain on themselves or strangers in exchange for money…the results are both concerning and promising.

The experiment involved 175 healthy adults, 89 of which were randomized to receive serotonin-boosting citalopram or placebo and the remaining 86 randomized to receive dopamine-boosting levodopa or placebo. The participants had to make choices in a harm aversion experiment regarding giving both themselves and other participants electric shocks for financial gain.

Entering separate testing rooms without seeing each other, the participants were given the drugs and waited until the peak drug absorption time was reached, 3 hours or 60 minutes for citalopram and levodopa respectively. With the drugs influence at its peak, the harm aversion experiment began.

86 times the participants were asked to decide between receiving either (i) a lower amount of money for less shocks to themselves or (ii) more money for more shocks. Likewise, they also had to make a choice 86 times about shocking anonymous strangers, where the participant had to decide on which tradeoff was better, (i) receive more money for themselves by inflicting a greater number of shocks to a stranger, or (ii) receive less money for themselves in order to electrocute the stranger a fewer number of times.

The researchers had previously published a study using the harm aversion experiment that revealed that most people show a greater aversion to inflicting pain on others than towards themselves, which they coined as being in a ‘hyperaltruistic disposition’.

However, in the present experiment, the participants in the test condition were given commonly prescribed drugs that influence the levels of common, multifunctional neurotransmitters in the brain that are involved in a myriad of cognitive functions, namely serotonin (citalopram) and dopamine (levodopa).

For those who experienced the pharmacological enhancement of serotonin by taking citalopram, they were more likely to avoid harming both themselves and others, choosing to receive less money rather than inflict pain compared with drug-free controls. This is promising news considering reduced harm aversion is a risk factor for both preplanned and in the moment reactive aggression that are both common features of the mental illnesses and disorders that citalopram and similar serotonin reuptake inhibitors are prescribed to treat.

Whereas those who experienced the pharmacological enhancement of dopamine by taking levodopa had a reduction in hyperaltruism, and were more likely to inflict pain on others than themselves compared with controls. Ultimately, this means that taking levodopa increases selfishness for monetary reward, which is backed by other studies.

Interestingly, the decision altering effects of both drugs were dose-dependent, meaning that the higher quantity of the drug that was taken, the stronger the effect was on moral decision making.

Looking at how quickly participants made decisions on both drugs was also enlightening when considering other research on uncertainty. With citalopram, it took longer for the participants to make their decision. The researchers interpreted this as ‘erring on the side of caution’ to avoid imposing unwanted levels of shocking pain on others.

However, it is also important to note that citalopram enhanced the participants’ negative affect, which includes negative emotions like anger, contempt, disgust, guilt, fear, and nervousness. It may be that enhanced worry and nervousness caused by healthy people taking citalopram and abnormally enhanced serotonin levels promotes harm aversion and cautious behavior, which may not be useful for overly harm avoidant, fearful, and withdrawn psychiatric patients.

With levodopa, on the other hand, the authors suggest a mechanism by which levodopa reduces hyperaltruism through boosted dopamine levels that reduces the variability of neural representations of other people. This reduced variability is thought to make the decision to cause pain quicker and easier than without levodopa, in line with the current neuroscientific perspective on empathy.

Dr Molly Crockett, lead author of the study reminds us that psychiatric drugs influencing moral decisions in healthy people has serious ethical implications for pharmacological interventions; however,

“It is important to stress…that these drugs may have different effects in psychiatric patients compared to healthy people. More research is needed to determine whether [and how] these drugs affect moral decisions in [the different groups of people] that take them for medical reasons.”


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Crockett, M., Kurth-Nelson, Z., Siegel, J., Dayan, P., & Dolan, R. (2014). Harm to others outweighs harm to self in moral decision making. Proceedings Of The National Academy Of Sciences, 111(48), 17320-17325. doi: 10.1073/pnas.1408988111

Crockett, M., Siegel, J., Kurth-Nelson, Z., Ousdal, O., Story, G., & Frieband, C. et al. (2015). Dissociable Effects of Serotonin and Dopamine on the Valuation of Harm in Moral Decision Making. Current Biology, 25(14), 1852-1859. doi: 10.1016/j.cub.2015.05.021

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Carla Clark, PhD

Carla Clark, PhD, is BrainBlogger's Lead Editor and Psychology and Psychiatry Section Editor. A scientific consultant, writer, and researcher in a variety of fields including psychology and neuropsychology, as well as biotechnology, molecular biology, and biophysical chemistry, you can follow her on Facebook or Twitter @GeekReports
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