Neonates experience adverse drug reactions (ADRs), but under‐reporting of suspected ADRs to national spontaneous reporting schemes in this population is particularly high. A prospective observational study collected suspected neonatal ADRs at a tertiary neonatal unit. Cases were analysed for causality by six assessors using three existing methods. Sixty‐three suspected ADR cases were identified in 35/193 neonates (18.1%). The proportion of suspected ADRs where the drug was prescribed “off‐label” was 30/68 (44.1%). When 34 cases were assessed for causality using three methods, global kappa scores of less than 0.3 for each tool suggested only “fair” inter‐rater reliability. Neonatal ADRs can be captured and occur from a variety of drugs affecting many organ systems. The current tools for assessing causality need to be adapted before they can reliably assess neonatal ADRs.