PurposeLoneliness disproportionately affects people with mental disorders, but associations with mental health outcomes in groups affected remain less well understood.MethodA cohort of patients receiving mental healthcare on 30th June 2012 was assembled from a large mental health records database covering a south London catchment area. Recorded loneliness within the preceding 2 years was extracted using natural language processing and outcomes were measured between 30th June 2012 until 30th December 2019, except for survival which applied a censoring point of 6th December 2020 according to data available at the time of extraction. The following mental healthcare outcomes: (i) time to first crisis episode; (ii) time to first emergency presentation; (iii) all-cause mortality; (iv) days active to service per year; and (v) face-to-face contacts per year.ResultsLoneliness was recorded in 4,483 (16.7%) patients in the study population and fully adjusted models showed associations with subsequent crisis episode (HR 1.17, 95% CI 1.07–1.29), emergency presentation (HR 1.30, 1.21–1.40), days active per year (IRR 1.04, 1.03–1.05), and face-to-face contacts per year (IRR 1.28, 1.27–1.30). Recorded loneliness in patients with substance misuse problems was particularly strongly associated with adverse outcomes, including risk of emergency presentation (HR 1.68, 1.29–2.18) and mortality (HR 1.29, 1.01–1.65).ConclusionPatients receiving mental healthcare who are recorded as lonely have a higher risk of several adverse outcomes which may require a need for higher service input.