Dose adjustments of Elexacaftor/Tezacaftor/Ivacaftor in response to mental health side effects in adults with cystic fibrosis

•A minority of adults with CF on ELX/TEZ/IVA experience deterioration in mental health.•Every effort should be made to continue ELX/TEZ/IVA while minimising side effects.•Dose adjustment may improvement mental health AEs in some individuals with CF.•Sweat chloride concentration may prove useful as a surrogate marker of CFTR function. Deterioration in mental health has been reported in a minority of individuals with cystic fibrosis starting elexacafor/tezacaftor/ivacaftor (ELX/TEZ/IVA). We report our experience of using sweat chloride and markers of clinical stability to titrate dose reduction with the aim of minimising adverse events and maintaining clinical stability. Adults (n = 266) prescribed ELX/TEZ/IVA, were included. Adverse events, sweat chloride, lung function and clinical data were collected. Nineteen (7.1%) individuals reported anxiety, low mood, insomnia and “brain fog” with reduced attention and concentration span. Thirteen underwent dose reduction with sweat chloride remained normal (