Introduction Acute severe behavioural disturbance (ASBD) is a condition seen with increasing frequency in emergency departments (EDs) in adults and young people. Despite the increasing number of presentations and significant associated risks to patients, families and caregivers, there is limited evidence to guide the most effective pharmacological management in children and adolescents. The aim of this study is to determine whether a single dose of intramuscular olanzapine is more effective than intramuscular droperidol at successfully sedating young people with ASBD requiring intramuscular sedation. Methods and analysis This study is a multicentre, open-label, superiority randomised controlled trial. Young people aged between 9 and 17 years and 364 days presenting to an ED with ASBD who are deemed to require medication for behavioural containment will be recruited to the study. Participants will be randomised in a 1:1 allocation between a single weight-based dose of intramuscular olanzapine and intramuscular droperidol. The primary outcome is the proportion of participants who achieve successful sedation at 1-hour post randomisation without the need for additional sedation. Secondary outcomes will include assessing for adverse events, additional medications provided in the ED, further episodes of ASBD, length of stay in the ED and hospital and satisfaction with management. Effectiveness will be determined using an intention-to-treat analysis, with medication efficacy determined as part of the secondary outcomes using a per-protocol analysis. The primary outcome of successful sedation at 1 hour will be presented as a percentage within each treatment group, with comparisons presented as a risk difference with its 95% CIs. Ethics and dissemination Ethics approval was received from the Royal Children's Hospital Human Research Ethics Committee (HREC/69948/RCHM-2021). This incorporated a waiver of informed consent for the study. The findings will be disseminated in a peer-reviewed journal and at academic conferences. Trial registration number ACTRN12621001238864.