Administration of painkillers has been shown to lower pain empathy, but whether this also reduces prosocial behavior is not known. In this preregistered study, we investigated whether inducing analgesia through a placebo painkiller reduced effortful helping. When given the opportunity to reduce the pain of another person, individuals experiencing placebo analgesia made fewer prosocial choices, helped less quickly, and exerted less physical effort when helping, compared to control participants with unaltered pain sensitivity. Furthermore, self-reported empathic unpleasantness positively correlated with prosocial choices across the whole sample. Reduced pain sensitivity thus not only influences empathy, as previously shown, but also negatively impacts prosocial behavior. Given the importance of prosociality for social cohesion, these findings have broad potential implications for both individuals under the influence of painkillers and for society at large.. See also the matching Twitter thread.