The remains of black henbane (Hyoscyamus niger) are relatively common at archaeological sites as it grows naturally around settlements in north-western Europe. All parts of the plant may be used as a medicine or a narcotic but its natural prevalence in built environments makes it difficult to interpret any intentionality behind its presence in the archaeological record. Evidence of the deliberate collection and use of black henbane seeds in the Roman Netherlands is presented here for the first time. Examination of Classical texts and interrogation of the archaeobotanical data allow the authors to place the discovery at Houten-Castellum of a hollowed bone containing hundreds of black henbane seeds within the context of the wider Roman understanding of the plant and its properties.