We describe how COVID-19-related policy decisions and guidelines impacted healthcare workers (HCWs) during the UK’s first COVID-19 pandemic phase. Guidelines in healthcare aim to streamline processes, improve quality and manage risk. However, we argue that during this time the guidelines we studied often fell short of these goals in practice. We analysed 74 remote interviews with 14 UK HCWs over 6 months (February–August 2020). Reframing guidelines through Mol’s lens of ‘enactment’, we reveal embodied, relational and material impacts that some guidelines had for HCWs. Beyond guideline ‘adherence’, we show that enacting guidelines is an ongoing, complex process of negotiating and balancing multilevel tensions. Overall, guidelines: (1) were inconsistently communicated; (2) did not sufficiently accommodate contextual considerations; and (3) were at times in tension with HCWs’ values. Healthcare policymakers should produce more agile, acceptable guidelines that frontline HCWs can enact in ways which make sense and are effective in their contexts.