Title {1}	Effectiveness of an app-based intervention to reduce substance use, gambling, and digital media use in vocational school students: study protocol for a randomized controlled trial
Trial registration {2a and 2b}.	Trial registration number DRKS00023788. Registered on 20 January 2021.
Protocol version {3}	The current protocol version is version 1.0, dated from 02 December 2021.
Funding {4}	The trial is funded by the Federal Ministry of Health Germany (BMG, grant number: ZMVI1-2519DSM216). The funding period is from 01 August 2019 to 31 December 2022. The funding source has no role in the design of this study and will not have any role in its execution, analyses, interpretation of the data, or decision to submit results.
Author details {5a}	NA, JW, RT: German Centre for Addiction Research in Childhood and Adolescence at University Medical Centre Hamburg-Eppendorf, Hamburg, Germany; KL, MR, LK: IFT Institut für Therapieforschung München, Germany; MM, BP, RH: Institute for Therapy and Health Research, IFT-Nord.
Name and contact information for the trial sponsor {5b}	Institute for Therapy and Health Research, IFT-Nord, Kiel, GermanyTrial’s principal investigator: Reiner Hanewinkel, hanewinkel@ift-nord.de; scientific coordinator: Matthis Morgenstern, morgenstern@ift-nord.de.
Role of sponsor {5c}	The sponsor is non-commercial. The sponsor ensures quality management, qualified and trained personnel, study protocol compliance, and submission of relevant study documents to the ethics committee and regulatory authorities. He supports the study with trial unit facilities and study personnel.