How should we punish criminal offenders? One prima facie attractive punishment is administering a mandatory neurointervention—“interventions that exert a physical, chemical or biological effect on the brain in order to diminish the likelihood of some forms of criminal offending”. While testosterone-lowering drugs have long been used in European and US jurisdictions on sex offenders, it has been suggested that advances in neuroscience raise the possibility of treating a broader range of offenders in the future. Neurointerventions could be a cheaper, and more effective method of punishment. They could also be more humane. Nevertheless, in this paper we provide an argument against the use of mandatory neurointerventions on offenders. We argue that neurointerventions inflict a significant harm on an offender that render them a morally objectionable form of punishment in a respect that incarceration is not. Namely, it constitutes an objectionable interference with the offender’s mental states. However, it might be thought that incarceration also involves an equally objectionable interference with the offender’s mental states. We show that even if it were the case that the offender is harmed to the same extent in the same respect, it does not follow that the harms are morally equivalent. We argue that if one holds that intended harm is more difficult to justify than harm that is unintended but merely foreseen, this means neurointerventions could be morally objectionable in a significant respect that incarceration is not.