Background: The incidence of hospital-presenting self-harm peaks among young people, who most often engage in intentional drug overdose (IDO). The risk of self-harm repetition is high among young people and switching methods between self-harm episodes is common. However, little is known about their patterns of repetition and switching following IDO. This study aimed to investigate repeat self-harm and method-switching following hospital-presenting IDO among young people. Methods: Data from the National Self-Harm Registry Ireland on hospital-presenting self-harm by individuals aged 10–24 years during 2009–2018 were examined. Cox proportional hazards regression models with associated hazard ratios (HRs), survival curves and Poisson regression models with risk ratios (RRs), were used to examine risk factors for repetition and method-switching. Results: During 2009–2018, 16,800 young people presented following IDO. Within 12 months, 2136 young people repeated self-harm. Factors associated with repetition included being male (HR = 1.13, 95% CI: 1.03–1.24), aged 10–17 years (HR = 1.29, 95% CI: 1.18–1.41), consuming ≥ 50 tablets (HR = 1.27, 95% CI: 1.07–1.49) and taking benzodiazepines (HR = 1.67, 95% CI: 1.40–1.98) or antidepressants (HR = 1.36, 95% CI: 1.18–1.56). The cumulative risk for switching method was 2.4% (95% CI: 2.2–2.7). Method-switching was most likely to occur for males (RR = 1.36; 95% CI: 1.09–1.69) and for those who took illegal drugs (RR = 1.63; 95% CI: 1.19–2.25). Conclusion: Young males are at increased risk of repeat self-harm and method-switching following IDO and the type and quantity of drugs taken are further indicators of risk. Interventions targeting IDO among young people are needed that ensure that mental health assessments are undertaken and which address access to drugs.