ABSTRACTObjectives:In the UK, Movicol paediatric plain (polyethylene glycol 3350 with electrolytes [PEG 3350+E], Norgine, UK), is licensed for chronic constipation in children 2 –11 years of age and faecal impaction (FI) from 5 years. This study aimed to investigate usage and characterise the risk profile in children under 2 years of age using PEG 3350+E in the UK.Methods:Retrospective, single exposure cohort study, with patients identified from Clinical Practice Research Datalink (CPRD) GOLD. Patients first prescribed PEG 3350+E under 2 years of age for the treatment of constipation or FI, between September 2003 and July 2019, were included.Results:There were 13,235 patients with a constipation indication and 40 patients with FI. For the constipation cohort: median age of PEG 3350+E first prescription was 1.2 years [interquartile range (IQR) 0.9, 1.6] and 68.4% had one treatment episode (TE). The mean duration of exposure, in the first TE, was 88.9 days. The most common total daily dose was one sachet (6.9 g).In terms of incident events on treatment, 0.5% of patients had abdominal pain, 3.0% had diarrhoea (may be attributed to treatment) and 4.1% had vomiting. 2.0% had signs/symptoms which could (in extreme cases) be associated with electrolyte disturbance, however, none had abnormal electrolyte values.Discussion:The safety aspect of this study did not identify any signals of concern in the constipation cohort. The number of patients in the FI cohort were too small for robust conclusions. If information were available, then a safety study would ideally assess treatment intake per kilogram, including electrolyte intake, before reaching safety conclusions. Nevertheless, these data contribute to real-world evidence on the use of PEG 3350+E in this population.