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 a lower amount of money for less shocks to themselves or more money for more shocks. Likewise, they also had to make choices 86 times for shocking anonymous strangers, where the participant had to decide on which tradeoff was better, receive more money for themselves by inflicting a greater number of shocks to a stranger, or receive less money for themselves in order to electrocute the stranger a fewer number of times.

The researchers had previously published a study of the harm aversion experiment that revealed that most people show a greater aversion to inflicting pain on others than towards themselves, which they coined being 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 had a 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 had a pharmacological enhancement of dopamine by taking levodopa had their hyperaltruism reduced, and were more likely to inflict pain on others than themselves compared with control. Ultimately, this means that taking levodopa increases selfishness for monetary reward, which is backed by other studies.

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

Looking at how quickly decisions were made on both drugs was also enlightening when considering other research on uncertainty. With citalopram it took longer for the participants to make their decision which the researchers interpreted 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 enhancing 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 reducing the variability of neural representations of other people, making the decision to cause pain a 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 of 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 [different groups of people] that take them for medical reasons.”


Main DOI:

Previous research: 10.1073/pnas.1408988111

Aggression and psycopath: 10.1016/0010-0277(95)00676-P

dopamine and selfishness: 10.1007/s00213-013-3210-x

empathy neuroscience: 10.1038/nn.3085

Carla Clark, PhD

Carla Clark, PhD, is BrainBlogger's Psychology and Psychiatry Section Editor and a scientific consultant, writer and researcher in fields including psychology and neuropsychology, as well as biotechnology, molecular biology and biophysical chemistry. She is also our newly appointed Digital and Social Media Manager. Follow her on Facebook or Twitter @GeekReports
See All Posts By The Author

Do not miss out ever again. Subscribe to get our newsletter delivered to your inbox a few times a month.