biostudies-literatureBye AMedical Research FoundationMaudsley NHS Foundation TrustNational Institute for Health Research (NIHR) Biomedical Research CentreMedical Research CouncilNuffield TrustAlan Turing InstituteNational Institute for Health and Care ResearchKing’s College LondonNIHR Clinical Research Network (CRN) South LondonMaudsley Biomedical Research CentreAcademy of Medical SciencesEngineering and Physical Sciences Research Councile0299059https://www.ebi.ac.uk/biostudies/studies/S-EPMC11111019biostudies-literatureUnknown19(5)<h4>Objectives</h4>The Social media, Smartphone use and Self-Harm (3S-YP) study is a prospective observational cohort study to investigate the mechanisms underpinning associations between social media and smartphone use and self-harm in a clinical youth sample. We present here a comprehensive description of the cohort from baseline data and an overview of data available from baseline and follow-up assessments.<h4>Methods</h4>Young people aged 13-25 years were recruited from a mental health trust in England and followed up for 6 months. Self-report data was collected at baseline and monthly during follow-up and linked with electronic health records (EHR) and user-generated data.<h4>Findings</h4>A total of 362 young people enrolled and provided baseline questionnaire data. Most participants PloS oneCohort profile: The Social media, smartphone use and Self-harm in Young People (3S-YP) study-A prospective, observational cohort study of young people in contact with mental health services.PMC11111019EP/N510129/1MR/S020365/1EP/V030302/1Williamson GCarr ETrevillion KVega Viyuela ALeightley DBranthonne-Foster SBye ADutta RLiakata MCarter BZenasni ZCross SfalseCohort profile: The Social media, smartphone use and Self-harm in Young People (3S-YP) study-A prospective, observational cohort study of young people in contact with mental health services.<h4>Objectives</h4>The Social media, Smartphone use and Self-Harm (3S-YP) study is a prospective observational cohort study to investigate the mechanisms underpinning associations between social media and smartphone use and self-harm in a clinical youth sample. We present here a comprehensive description of the cohort from baseline data and an overview of data available from baseline and follow-up assessments.<h4>Methods</h4>Young people aged 13-25 years were recruited from a mental health trust in England and followed up for 6 months. Self-report data was collected at baseline and monthly during follow-up and linked with electronic health records (EHR) and user-generated data.<h4>Findings</h4>A total of 362 young people enrolled and provided baseline questionnaire data. Most participants 2024-01-01T00:00:00Z20242026-06-03T06:51:06.077Z2026-04-25T03:22:08.312ZS-EPMC111110193877626110.1371/journal.pone.0299059